Welcome to the contributors' manual!

This guide is open and publicly editable. You can find it's sources in our gitlab repository.

If you find any section of this guide lacking, don't hesitate to update this guide, open a PR or send us a patch!

Social Documentation

Contributing to a FOSS project always has a social component. Whether you are providing a patch, a new feature or other content, knowing where and how to engage with the project will make everybodies lives easier.


The projet uses IRC as development and social chat. Feel free to drop by!

We also have an announcement mailing list, which is very low volume.

If you don't want to or can't use zulip, we also have a community mailing list, which is mixed volume. You can post questions there, show off your projects using libqaul or submit patches to the project!

Code of Conduct

TLDR: be nice!

We want to foster an open and engaging atmosphere for and the development community around it. Because of this we follow the "Contributor Covenant" code of conduct. A copy of it should have been included in the sources for this book.

How to contribute?

First of all: you're cool! 😎

Development of happens mostly on Open Communication with an open development & support chat on IRC channel. If you have any questions getting started, please come by!

Submitting a PR

  • If a relevant issue exists, please tag in your description, not the title.
  • Include a short description of the accumulative changes
  • If you want your history to be rebased/ merged, please clean it up to be useful. Otherwise we will probably squash it.
  • Feel free to open a work-in-progress PR as a place to have a discussion about changes or to get feedback.

Submitting an e-mail patch

If you can't contribute via github (for whatever reason), you're very welcome to submit your patch via e-mail.

The easiest way of doing this is to configure git send-email. Patches should be submitted to the community mailing list at ~qaul/


  • Send an e-mail with the title [PATCH]: <your title here>.
  • Format your patch with git diff -p
  • Don't send HTML e-mail!
  • Make sure your line-wrapping is wide enough to allow the patch to stay un-wrapped!

Contributor Covenant Code of Conduct

Our Pledge

In the interest of fostering an open and welcoming environment, we as contributors and maintainers pledge to making participation in our project and our community a harassment-free experience for everyone, regardless of age, body size, disability, ethnicity, gender identity and expression, level of experience, nationality, personal appearance, race, religion, or sexual identity and orientation.

Our Standards

Examples of behavior that contributes to creating a positive environment include:

  • Using welcoming and inclusive language
  • Being respectful of differing viewpoints and experiences
  • Gracefully accepting constructive criticism
  • Focusing on what is best for the community
  • Showing empathy towards other community members

Examples of unacceptable behavior by participants include:

  • The use of sexualized language or imagery and unwelcome sexual attention or advances
  • Trolling, insulting/derogatory comments, and personal or political attacks
  • Public or private harassment
  • Publishing others' private information, such as a physical or electronic address, without explicit permission
  • Other conduct which could reasonably be considered inappropriate in a professional setting

Our Responsibilities

Project maintainers are responsible for clarifying the standards of acceptable behavior and are expected to take appropriate and fair corrective action in response to any instances of unacceptable behavior.

Project maintainers have the right and responsibility to remove, edit, or reject comments, commits, code, wiki edits, issues, and other contributions that are not aligned to this Code of Conduct, or to ban temporarily or permanently any contributor for other behaviors that they deem inappropriate, threatening, offensive, or harmful.


This Code of Conduct applies both within project spaces and in public spaces when an individual is representing the project or its community. Examples of representing a project or community include using an official project e-mail address, posting via an official social media account, or acting as an appointed representative at an online or offline event. Representation of a project may be further defined and clarified by project maintainers.


Instances of abusive, harassing, or otherwise unacceptable behavior may be reported by contacting the project team at All complaints will be reviewed and investigated and will result in a response that is deemed necessary and appropriate to the circumstances. The project team is obligated to maintain confidentiality with regard to the reporter of an incident. Further details of specific enforcement policies may be posted separately.

Project maintainers who do not follow or enforce the Code of Conduct in good faith may face temporary or permanent repercussions as determined by other members of the project's leadership.


This Code of Conduct is adapted from the Contributor Covenant, version 1.4, available at Web Services runs many different web services:

This chapter explains how they are hosted, updated, where to look to edit and change them and who to contact when the service is not working or you would like to have access to it. Web Site

There is an own chapter in this guide on the editing of the web site. Please have a look there on how to edit and translate the web site.

  • Server:
  • Source repository:
  • Updated: by deploy script
  • Admin contact: Documentation

The software documentation & guides of

  • Server:
  • Source repository:
  • Updated: by deploy script
  • Admin contact: Download Directory

The Download server for the binary builds and big content files such as videos etc.

  • Server:
  • Updated:
    • the builds are uploaded by CI
    • content is uploaded manually by the administrators
  • Admin contact:

Technical Documentation

Welcome to the technical documentation!

This section is aimed at two different types of people:

  1. People wanting to contribute to and it's libraries
  2. People wanting to write their own apps for a qaul network

This page will offer a short introduction to the project structure to get you started. On each section in this document there are pages and chapters that go into more detail than is required here.


Fundamentally, is a highly distributed system. As such, it is not accountable to a single set of rules across all devices that are part of this system. It is important to make the distinction between "", the application, "qaul network", the distributed network of devices, and other components provided by the project that can be used to write decentralised applications.

The primary component in this ecosystem is called libqaul. It provides an abstraction layer for a distributed network of devices, the users that interact with each other and the messages and data that can be exchanged. The API of this library is called the "service API" in other parts of the docs.

Built on top of it are services (or apps), that provide more specific functionality, such as text messaging or file sharing. (the app) is merely a GUI and collection of a few different services all running on the same libqaul instance on one device.


The following sections will outline the different layers present in (the application), then there are pages for more details on how to interact with each of these layers.

Services & apps

As mentioned in the introduction it is possible to build applications (or "services") with libqaul, that can interact with each other on a distributed network. These services provide high level functionality such as sending text messages, a collaborative public feed (similar to mastodon), and voice calls.

Following is a list of all the services that come bundled in by default (more details here).

  • feed
  • messages
  • files
  • voices
  • radio

The reason why is built in such a modular way is to allow you to write your own services, with their own functionality and UI, that gets to interact with an existing service and user ecosystem. libqaul also helps you to build your application in a way where it doesn't rely on central servers on a network and keeping your users' data safe.


Service API

The interface to libqaul is called the service API, and a versatile abstraction over a decentralised network. It handles local user authentication, network user discovery, binary payload messages, contact data, and even encrypted file storage at rest.

The API itself is available as an async Rust library and ffi C interface, with some optional IPC add-ons:

  • http/json:api - this is how the GUI is hooked up
  • socket-ipc - using a cap'n proto ipc protocol over unix sockets
  • android-ipc - implementing an Android specific ipc interface

The idea behind the variety of IPC interfaces is that your application can bundle it's own copy of libqaul, to provide the network backends required to join a mesh network, however it can also connect with a running instance if one is available, seeing as only one daemon can concurrently have access to the networking backends.

This way resources, user profiles and social graphs can be shared. Furthermore, it's possible for your application to use services that are bundled in with a application stack, meaning that there's a lot of functionality that you don't have to replicate in your own apps.


The internals of libqaul are intirely written in Rust, and hook into various storage and networking abstractions. libqaul primarily uses two libraries, also written as part of this project, to do it's job: alexandria, and ratman.


As mentioned in the introduction, it's important to make the distinction between the ecosystem of libraries (documented after this section), a "qaul network", consisting of meshed devices, and "" the application that you can install on your phone and laptop. is a collection of services written by the project developers themselves and kept in the same tree as the libraries that power them. It provides a GUI on various platforms that is meant as a referenc implementation for third-party developers.

The following pages will outline the services that get bundled into, what they can do and how you can use them in a third-party application. services

Following is a list of services that are bundled in with, and what they can do for you.

Important because we're still in development, some of these services don't exist yet! If you find one that doesn't and you think you would have fun implementing it, get in touch!


  • Service ID: net.qaul.feed
  • Crate name: qaul-feed

Public message feed, similar to micro-blogging applications such as mastodon or twitter. Users can compose short-medium length messages that get shared with the whole network. You have the choice of filtering by "all messages" and "only following", where you can only display messages sent by friends or people you trust.


  • Service ID: net.qaul.messaging
  • Crate name: qaul-messaging

Private (1-to-1 or groups) text messaging, that can optionally (by default) be encrypted. Conversations can either be displayed as a feed (like chat), or threaded (like e-mail). Files can be sent either in-line (if the payload is small enough), or via file-announce messages that use the "files" service.


  • Service ID: net.qaul.files
  • Crate name: qaul-files

Filesharing via announce-links similar to how torrents get announced on trackers. You can announce a file to either a group of people, a singe user, or the whole network. Optionally this service can be configured to download all files that were publicly announced to allow servers to replicate a "public archive" that users can have access to, if the original source of a file disappears.


  • Service ID: net.qaul.voices
  • Crate name: qaul-voices

Integrates with various platform features to allow voice call streaming over the, as well as preparing audio messages that can be inlined into messages, or sent to many people via announce links.


  • Service ID:
  • Crate name: qaul-radio

Similarly to voices, it integrates into platform features to provide audio capture and playback, but for one-to-many streams. This way people can broadcast themselves into the network, while others can tune into a program, without being able to respond. Similar to files, this service can be configured to automatically archive radio broadcasts for community servers.


This chapter deals with libqaul, and it's various parts, and use cases. Depending on what you want to do, different aspects of the library will be important to you, and as such, the information is split into different sections, tailored to different users.

Service API

This section of the manual covers the service API. Please check the libqaul Rust API docs for actual function docs. This document will go into the concepts more than actual code.

The API is written in Rust and uses async/await futures, built with the async-std runtime. If you build a service in Rust, we recommend you use the same runtime to keep the application binary as small as possible.

Code and function docs for libqaul can be found here!


At the heart of almost every call to the service API is a user session. You can use the login and logout functions to manipulatio a session. The user authentication object, containing the user's ID, and a token assigned with your session, is required for every subsequent call into the API. Tokens will also expire with inactivity, so building your code to be resistent to Error::NoAuth errors is always a good idea.

Attached to a user comes a message, contacts and file store. A global user store also exists. These are provided by function scope endpoints, that encapsulate various functions in a type/namespace to make interacting with them easier.

User store

An instance of libqaul keeps track of users on the network, and general user announcements, which are saved in the user store. These user profiles are slowly filled with metadata, as more information becomes available about a user: did they set an avatar recently, do they have a preferred nickname or pronouns, etc.

It's also possible to search by any attribute in the store, even optional user generated fields like location.

Mesage store

For each user, a message store overlay is kept, meaning that an instance only keeps one copy of the actual messages, but what user has access to them changes what part of the store they can see. Similar to the user store, it's possible to send queries to the store to get messages sent to the current user and service, according to a parametric search.

Contact book

Each user also keeps a private contact overlay, in which they can annotate users they have interacted with. Available fields are trust, if two users have met, and free-form additional metadata.


Because libqaul already has a mechanism in place to encrypt data for a user at rest, this mechanism is exposed in the API to external services. On one hand this API can be used to store additional metadata for a service, that is required to make it all work, or to get files that the user has discovered on the network and that were downloaded previously.

This API scope is complemented by the "files" endpoint, that provides a way to announce, pack, update and send files into a network. Note maybe it would make more sense to join "files" and "storage", and move the "files" functionality entirely into the files service.

libqaul IPC interfaces

While libqaul and all of the services are written in Rust, that doens't mean that you need to write your application in Rust. Especially considering that your application might want to connect to an already running daemon on a system, your application needs to connect to it in some way.

This is where the IPC interfaces come in (yes, ther's a few).

The HTTP/json:api interface was primarily written for the webgui, but it also exposes the core libaul functions, so can be used by your application. Check out the external book for the API.

Additionally there are more interfaces that are documented in this chapter. Furthermore, if you think that there's a benefit in building a new IPC interface for libqaul, get in touch! We're very curious.

Cap'n proto sockets

One way to inteact with libqaul is via the libqaul-ipc crate which implements the same API as libqaul, while tunneling all calls through a previously negotiated unix socket, using the cap'n proto IPC protocol.

The same ffi C interface as for libqaul can be used, meaning that it's possible to write a service that uses this high-performance IPC channel from nearly any language.

More docs to follow, as this is still WIP!

Android Intents

Because on Android we are subject to sandboxing, we need to integrate into the intents ecosystem that can be used to send messages between apps.

More docs to follow as this is still being planned.

libqaul internals

This section of the manual covers parts of libqaul not exposed directly via the API. It's primarily useful to learn to debug behaviour, and for future contributors to get up to speed with the internal structure.

Most of the components exposed via the API have an internal component that acts as a strongly typed store (messages, users, contacts, files, ...). Some more interesting components are those that are not exposed.

Key store

Similar to the user and message store, libqaul stores public keys that it comes across, for later. This is meant to opportunisticly fill the store with keys that can be user later on to send encrypted messages or verify signatures.

The store is shared between users, but never exposed to users so that keys don't have to be fetched multiple times, but it's not neccessarily possible for a user to figure out the social cycle of one of their peers.


When a user is active on the network, this module sends out regular "announcements" that are used to keep the routing tables up with topology changes, as well as updates to local users. Some seeds are opportunistic, such as throwing out a public key, others are reactive, driven by data requests that are picked up by the discovery module.

There are several strategies that can be chosen when seeding data into the network, which should be given their own page soon.


The inverse of seeding to the network is the discovery module which reacts to user seeds. It will insert new users into the user store, relay messages to the appropriate service, or dropping them if no service handler was found.


The presistence module is implemented mostly by wrapping internal libqaul types with [alexantria] storage callbacks, which is the library which implements all of the persistence logic and at-rest encryption. It is developed as part of, but pulled out of the main tree to make it easier to use in other projects.


All calls to actually send data into a qaul network are implemented by Ratman, the delay tolerant, distance vector based routing protocol built specifically for You can find documentation specifically for it in later sections of this manual.


This is the documentation tree for the decentralised, delay-tolerant vector routing protocol "Ratman". It's basic design is influenced heavily by protocols such as B.A.T.M.A.N., serval, and others.

In Ratman, all routing is done on IDs that are represented as the blake2 hash of a user's public key. It has a real-time and buffered routing component: routing tables are built in userspace over a list of interfaces and interface specific IDs (not the pubkey!), to associate a pubkey with an interface route. This relationship is further explained in the netmod documentation.

If Ratman isn't able to find a route to a target, or based on various parameters, it will cache a message in the local journal, periodically checking if it can be delivered at a later point in time.

Ratman API

There's multiple scopes in the API that are responsible for doing vastly different things. This is due to how ratman can be used. Within libqaul we use all three scopes throughout the application lifecycle, but this isn't necessarily the case for all users of Ratman.

Interface setup

Because ratman does routing based on IDs and maps them to interfaces, these links represent a network space reachable through them that will allow a packet to be routed to it's final destination. We call these interface implementations "drivers" (more to that in the netmod docs).

Some are long-living, like the udp-netmod driver which grabs a local network and relays traffic via multicast and unicast, others are short-lived, such as the mem-netmod, which only represent a 1-to-1 link. If the topology of the network were to change, the link gets destroyed and cleaned up.

And that's what this API enables: a platform specific client which wraps around various drivers can inject them into ratman, and teach it about the network spaces that lie beyond in order to build up the routing table.


Using ratman to actually route traffic is pretty self explanatory: you pass in a message (which is a ratman abstraction), in looks up where to send it, slices it into frames according to the recomended packet size for the link, and then dispatches it.

Key and social callbacks

While the basic routing protocol is pretty simple there are ways to suppliment it. These callbacks are optional and ratman will happily route packets without having access to this data (in fact you can disable the features at compile time). The idea is that having access to a social graph for the routing can have positive effects on how fast a packet can reach it's destination. More docs to follow here, mostly because a lot of it is based on pretty new network research.


This library is an abstraction that provides an interface and packet specification that's used to communicate between Ratman and the network drivers (also called "netmods").

The actual API is pretty simple: it provides functions to send and poll for frames, provide a size hint (can be ignored), and link strenth (used to break ties in the routing table). Each call to send and next will yield an extra "target" id which is also stored my ratman to resolve one-to-many netmod links (like the udp one).

The API is also available from an ffi context where the I/O calls are made blockingly.

Implementing a netmod in C++

The following docs are mostly notes and should be revised later.

Start by creating a type that can be used in C land. Give it all the state it needs (here that means none).

fn main() {
struct MyFfiDriver;

We also need some functions to inject state into, and constructing the type:

fn main() {
extern "C" {
    fn ffi_driver_new() -> MyFfiDriver { ... }
    fn give(f: Frame) -> MyFfiDriver { ... }
    fn take() -> Fram { ... }

Make it implement the Endpoint and NativeEndpoint traits provided by netmod (compiled with ffi support enabled).

fn main() {
impl Endpoint for MyFfiDriver {
    // ...

You can then make the Endpoint methods call the native methods where appropriate, and the other way around.

In C++ land you can then include the netmod.h header, and use your type that you construct via some additional out-of-trait constructor:

#include <ratman/netmod.h>

auto mod = ffi_driver_new();

mod.give(my_frame); // this is returned on 'next()' call

auto frame = mod.take(); // We can send this now




Beta Report | Braindump

This and the following pages are a brain dump, written on (check following dates), outlining the current state of affairs, things that need to be worked on, and things that I (Katharina) don't have the capacity to work on right now. When outlinging things that are too complex to solve for me right now, I will try to provide as much context as possible, both for my future self, as well as other contributors.

If you see any open questions in this document, and you think you can help, please send an e-mail to the mailing list, or, if you're shy, to me personally:

Service API

As of 2020-01-13 the service API is looking pretty good. I've been hacking on the project full time for ~4 months or so, and there's been a lot of progress. All basic message functions are implemented, user creation, authentication, etc. Services can be registered and managed internally, and can pass mesages through the stack, and receive them as well. All API endpoints are doing blocking IO, meaning that callbacks are only done via lambdas.

One paint point here is that we want to move to all async IO, not for speed but mostly for simplicity in our own scheduling. async-std implements a good scheduler and it'll be easier for us to use this, than doing our own stuff with threads. Nora has been working on this a bunch and the current state (that don't build) are on the async branch on upstream.

Storage and identity secrecy

An issue that Jess raised a few days ago (as of 2020-10-13) was service storage: if we allow people to write services that handle user data, how do we make sure that they don't just drop that data on the FS and call it a day? Furthermore, how do we encourage people to write services that can have their IDs wiped without going all awol, i.e., we want to encourage ephemeral IDs for activist networks.

A solution to this is that we provide a storage API via libqaul, that people can use to store arbitrary data that they think is important to do their whole thing.

One issue that I, and others came up with is where to then store this data, but also how to avoid sidechannel attacks from a malicious service that might leak user metadata, i.e. what user uses what service? This is a bit of an open question because on one hand we want users to be able to announce services, but it should also be possible to run hidden services, that might not be legal to run. Furthermore, how do we design an abstraction over the secure store provided by alexandria (also wip) that doesn't fall victim to a padding-oracle-like attack, i.e. a service that can send queries for various users and services and looking at the failure responses to figure out what user is running what services. There's another layer to this, which is that we do expose a list of local IDs via a user endpoint so that the frontend can render a list of users to login as, for someone to just select. This obviously means that any code running on the user's device will have access to the list of users on the device.

One possible mitigating factor here would be to have users marked as "secret", where even libqaul itself doesn't know if it owns data for a user. A user would provide a secret, and their own key, similar to how the detached identities hash challenge works (outlined later?), to decrypt a user manifest and the load all the state from alexandria. This would mean that a user is unknown to peers outside of the current user session, or by dumping the libqaul memory space from a priviledged user (but honestly, if an adversary owns your device there's very little you can do - we should look into if mbedtls supports linux secmem extentions!)

As for hidder services for a user, we can use the same mechanism as the hidden user directory, except that we generate a secret for a service which is required when performing service lookup queries. When a user signs in, we can load the hidden service secrets from the user manifest, then unlock the service data, which is ambiguated at rest. If a malicious service tries to check for a service on a user by trying to load certain files from storage, it will require the service auth token which was only handed to the hidden service. The initialisation of the hidden service then follows another challenge response mechanism, similar to how we can load a hidden user: the hidden service generates a token, the user uses a trusted app to auth that token, then the serice secret is passed to the hidden service. Again, if the attacker can dump memory... etc etc.

I think these threat models are realistic, and my solutions offer a viable protection mechanism against them. There's some open questions, but this should be enough te implement the required endpoints in the service API now. I would suggest either adding a storage endpoint, or expanding the service endpoint if there aren't too many functions.

Malicious daemon

Not something that I want to write as much about here because the problem has way more factors and this is not a part of security analysis that I know much about (see previous section for application and protocol security): system integration and malicious daemons.

Say a user installs a malicious instance of libqaul, and it registers itself with dbus, intents, etc and now other applications, possibly our app itself, will start talking to it. Is there anything we can do?, the app, could pin it's daemon, but that would be annoying, especially because it could deter any app from connecting to any daemon, rendering the whole point of the API useless.

Shipping keys doesn't work (lol, why do people keep trying this?), maybe we could get people to checksum their binaries? But also hard. Anyway, I'll move on because there's more to cover.

Ratman, routing and async (again)

The current state in ratman is a mess. Messages can be routed, but floods don't work because they don't get deduplicated. To do this well, we need to finish the journal, which should index frames by ID, and then refuse to broadcast when it has already send a specific frame ID. Also, there's a lot of mising logic to rebuild the sliced messages, and also I had a conversation at 36c3 about doing the slicing in a more clever way. TODO: message Jeff.

When it comes to asyncing, there's a lot of work to do: ratman itself needs to get async internals so that we can actually call the netmod interface that now exists, but also we need to make sure that we can wrap blocking calls properly? Like, how do we call into native drivers that can't do async in Rust? I have some ideas about how to build the interfaces up on the async branch, but this all needs integration and I'm drawing a blank how this will actually look in C++, so maybe it's time to actually build the Android abstractions? I don't know.

After Ratman has an async API towards libqaul we need to async the core of that, and also make sure that we give Ratman a similar abstraction for the native code because let's remember that initialisation of a stack happens from the bottom up and all these APIs are gonna have to be wrapped for C++!

Hmm... I might have missed some things, but that's been making me anxious for the last 2 weeks or so. Please talk to me about these things if you have ideas, thoughts or suggestions.

Check the "Challenges" section following this, for some ideas that you (yes you!) could get started with, if you wanted to help out with developing


You wanna help? You're so cool ❤ Here's a list of things that need doing, similar to how an issue tracker would outline them. We'll try to keep this list up-to-date, and also always feel free to e-mail the "community" mailing list for feedback or ask on IRC!

Filesharing service

That sounds hard, but it's not that hard! There's no abstractions for you to introduce because libqaul provides all of them for you! Now, we might end up removing this abstraction from libqaul again, and moving it to the service entirely, but that can be done later.

There's "File", "FileMeta", and "FileFilter". We need to provide people with an API with which they can announce, send and query for files. The service API itself needs to take a file, serialise it with "conjoiner_engine", the same serialiser user all over libqaul and the messaging service (just check there how to use it), and send them out as messages to either the entire network (as a "fileannounce type"), or just to one person.

When the service get's a "FileRequest" (TODO: add that type to "FileMeta", it needs to load the file from disk, and then send it.

If you have questions, don't hesitate to ask!

UDP driver testing

There's netmod-udp in the tree, and while it's mostly (?) done, it could use some testing. Best to just ping spacekookie or pbb on IRC or the mailing list for this, as it's a bit more vague.

Translators Guide

For the translation of the web site please see the chapter Translate the Web Site.

Design Guide Web Site

This document is about the editing, translating and building the public web site which is availabe under

The web site is built via the static site generator HUGO. Its content and sources are hosted in a github repository and are community editable.

Your welcome to update, translate, open a PR or send us a patch!

Web Site Development Quick Start

Install HUGO

HUGO can be installed on almost every platform. Learn how to install it on your computer on

You need HUGO version 0.55 or newer to be able to test and run the web site. To check your installed version you may run the following command:

hugo version

Get the Web Site Sources

Clone or download the github repository of the web site. All needed files (templates, content, images) are in this repository.

git clone

Run and Test the Web Site locally

# move into your 
cd qaul-website

# start test server
hugo serve

Open the test web site in your web browser http://localhost:1313. When editing the web sites source files, you will see the changes immediately.

Troube Shooting

If you're geting an error without changing anything, check your installed HUGO version (run hugo version on the command line). You need at least version 0.55 or later to be able to run and test the web site.

Edit the Web Site

Here a quick overview of the web sites file structure:

  • HTML, CSS & JS Templates
    • theme folder contains all the HTML, CSS and javascript templates themes/hugo-theme-qaul. The only exception is the HTML template of the start page.
    • The HTML template of the start page is in layouts/index.html
  • Web site content
    • The markdown content files and the images are all residing in the content folder.
    • The start page content can be found in the content/ file and in the content/home folder. There is a file for each section of the start page.
    • All the tutorials are in sub folders of content/tutorials. Please see the chapter Write a Tutorial.

For translating the web site see the chapter Translate the Web Site.

Write a Tutorial

The tutorials can be easily created. This guide explains how.

Each tutorial is an own folder in the /content/tutorials folder in the web site repository. Please have a look at the existing tutorials to get an idea how this is done.

Here a step by step explanation on how to create a turial:

  1. Create a new folder for your tutorial. Give this folder a meaningful name (without spaces or special characters in it).
  2. Put all the images and files into your tutorial folder.
  3. Create an file in your tutorial folder.
    • If you write the tutorial in another language than English, make the two letter language code part of the file name. e.g. for French.
    • Write your tutorial in text-editor. The text needs to be formated in markdown.
    • Link your files and images in the tutorial.
    • Set the tutorial meta information in the tutorial header
      • title the title of your tutorial
      • preview the filename of an image in your tutorial folder which is used as a thumbnail image in the tutorial overview page.
      • tags define some tags that categorize the topic of your tutorial. They will be shown in the tutorial overview and in your tutorial.

Here an example file

title: 'My first Tutorial'
preview: previewImage.jpg
- MyTag
- AnotherTag
# This is my first Tutorial

This is the first paragraph of my tutorial with text formated in **bold** and *italic*.

Below will be shown the first image in my tutorial:

  1. Once you finished editing, you are ready to publish the tutorial. If you know how to use git, send us a pull request, otherwise please send a download link to the mailing list.

Translate the Web Site

The web site is multilingual and can be translated into any language.

Translating a Content Page

Each page can be translated in any Language. The

Adding a New Language

To add a new language there are only a few things to do:

  1. Add the new language to the configuration file config.toml. Add the new language to the existing configuration:
    weight = 1
    LanguageName = "English"
    weight = 3
    LanguageName = "Deutsch"
    weight = 2
    LanguageName = "العربية"
    rtl = true
  1. Create a language specific CSS file in the folder themes/hugo-theme-qaul/static/css/ (e.g. themes/hugo-theme-qaul/static/css/fr.css for French).
  • This file contains language specific configuration and will mostly be empty.
  • For right-to-left written languages copy the file for arabic 'ar.css'.
  1. Translate the web site menu items. The web site menu items can be found in the folder themes/hugo-theme-qaul/i18n. There is a file for each language.
  • Copy the file en.toml and rename it according to your language.
  • Translate each sentence or word in other = "TRANSLATE THIS PART".
  1. Translate the content markdown files. The markdown files are in the content folder.
    • Try to at least translate the start page. The following files need to be translate for the start page:
      • content/
      • all files in the folder content/home
    • Read the section Translating a Content Page for how to translate a content page.

Legal is a fully free and open source software. It is licensed under the GPL license (Version 3).

The documentation & web site of stay under the Creative Commons Attribution 4.0 International license.


Version 3, 29 June 2007

Copyright (C) 2007 Free Software Foundation, Inc.

Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed.


The GNU General Public License is a free, copyleft license for software and other kinds of works.

The licenses for most software and other practical works are designed to take away your freedom to share and change the works. By contrast, the GNU General Public License is intended to guarantee your freedom to share and change all versions of a program--to make sure it remains free software for all its users. We, the Free Software Foundation, use the GNU General Public License for most of our software; it applies also to any other work released this way by its authors. You can apply it to your programs, too.

When we speak of free software, we are referring to freedom, not price. Our General Public Licenses are designed to make sure that you have the freedom to distribute copies of free software (and charge for them if you wish), that you receive source code or can get it if you want it, that you can change the software or use pieces of it in new free programs, and that you know you can do these things.

To protect your rights, we need to prevent others from denying you these rights or asking you to surrender the rights. Therefore, you have certain responsibilities if you distribute copies of the software, or if you modify it: responsibilities to respect the freedom of others.

For example, if you distribute copies of such a program, whether gratis or for a fee, you must pass on to the recipients the same freedoms that you received. You must make sure that they, too, receive or can get the source code. And you must show them these terms so they know their rights.

Developers that use the GNU GPL protect your rights with two steps: (1) assert copyright on the software, and (2) offer you this License giving you legal permission to copy, distribute and/or modify it.

For the developers' and authors' protection, the GPL clearly explains that there is no warranty for this free software. For both users' and authors' sake, the GPL requires that modified versions be marked as changed, so that their problems will not be attributed erroneously to authors of previous versions.

Some devices are designed to deny users access to install or run modified versions of the software inside them, although the manufacturer can do so. This is fundamentally incompatible with the aim of protecting users' freedom to change the software. The systematic pattern of such abuse occurs in the area of products for individuals to use, which is precisely where it is most unacceptable. Therefore, we have designed this version of the GPL to prohibit the practice for those products. If such problems arise substantially in other domains, we stand ready to extend this provision to those domains in future versions of the GPL, as needed to protect the freedom of users.

Finally, every program is threatened constantly by software patents. States should not allow patents to restrict development and use of software on general-purpose computers, but in those that do, we wish to avoid the special danger that patents applied to a free program could make it effectively proprietary. To prevent this, the GPL assures that patents cannot be used to render the program non-free.

The precise terms and conditions for copying, distribution and modification follow.


0. Definitions.

"This License" refers to version 3 of the GNU General Public License.

"Copyright" also means copyright-like laws that apply to other kinds of works, such as semiconductor masks.

"The Program" refers to any copyrightable work licensed under this License. Each licensee is addressed as "you". "Licensees" and "recipients" may be individuals or organizations.

To "modify" a work means to copy from or adapt all or part of the work in a fashion requiring copyright permission, other than the making of an exact copy. The resulting work is called a "modified version" of the earlier work or a work "based on" the earlier work.

A "covered work" means either the unmodified Program or a work based on the Program.

To "propagate" a work means to do anything with it that, without permission, would make you directly or secondarily liable for infringement under applicable copyright law, except executing it on a computer or modifying a private copy. Propagation includes copying, distribution (with or without modification), making available to the public, and in some countries other activities as well.

To "convey" a work means any kind of propagation that enables other parties to make or receive copies. Mere interaction with a user through a computer network, with no transfer of a copy, is not conveying.

An interactive user interface displays "Appropriate Legal Notices" to the extent that it includes a convenient and prominently visible feature that (1) displays an appropriate copyright notice, and (2) tells the user that there is no warranty for the work (except to the extent that warranties are provided), that licensees may convey the work under this License, and how to view a copy of this License. If the interface presents a list of user commands or options, such as a menu, a prominent item in the list meets this criterion.

1. Source Code.

The "source code" for a work means the preferred form of the work for making modifications to it. "Object code" means any non-source form of a work.

A "Standard Interface" means an interface that either is an official standard defined by a recognized standards body, or, in the case of interfaces specified for a particular programming language, one that is widely used among developers working in that language.

The "System Libraries" of an executable work include anything, other than the work as a whole, that (a) is included in the normal form of packaging a Major Component, but which is not part of that Major Component, and (b) serves only to enable use of the work with that Major Component, or to implement a Standard Interface for which an implementation is available to the public in source code form. A "Major Component", in this context, means a major essential component (kernel, window system, and so on) of the specific operating system (if any) on which the executable work runs, or a compiler used to produce the work, or an object code interpreter used to run it.

The "Corresponding Source" for a work in object code form means all the source code needed to generate, install, and (for an executable work) run the object code and to modify the work, including scripts to control those activities. However, it does not include the work's System Libraries, or general-purpose tools or generally available free programs which are used unmodified in performing those activities but which are not part of the work. For example, Corresponding Source includes interface definition files associated with source files for the work, and the source code for shared libraries and dynamically linked subprograms that the work is specifically designed to require, such as by intimate data communication or control flow between those subprograms and other parts of the work.

The Corresponding Source need not include anything that users can regenerate automatically from other parts of the Corresponding Source.

The Corresponding Source for a work in source code form is that same work.

2. Basic Permissions.

All rights granted under this License are granted for the term of copyright on the Program, and are irrevocable provided the stated conditions are met. This License explicitly affirms your unlimited permission to run the unmodified Program. The output from running a covered work is covered by this License only if the output, given its content, constitutes a covered work. This License acknowledges your rights of fair use or other equivalent, as provided by copyright law.

You may make, run and propagate covered works that you do not convey, without conditions so long as your license otherwise remains in force. You may convey covered works to others for the sole purpose of having them make modifications exclusively for you, or provide you with facilities for running those works, provided that you comply with the terms of this License in conveying all material for which you do not control copyright. Those thus making or running the covered works for you must do so exclusively on your behalf, under your direction and control, on terms that prohibit them from making any copies of your copyrighted material outside their relationship with you.

Conveying under any other circumstances is permitted solely under the conditions stated below. Sublicensing is not allowed; section 10 makes it unnecessary.

3. Protecting Users' Legal Rights From Anti-Circumvention Law.

No covered work shall be deemed part of an effective technological measure under any applicable law fulfilling obligations under article 11 of the WIPO copyright treaty adopted on 20 December 1996, or similar laws prohibiting or restricting circumvention of such measures.

When you convey a covered work, you waive any legal power to forbid circumvention of technological measures to the extent such circumvention is effected by exercising rights under this License with respect to the covered work, and you disclaim any intention to limit operation or modification of the work as a means of enforcing, against the work's users, your or third parties' legal rights to forbid circumvention of technological measures.

4. Conveying Verbatim Copies.

You may convey verbatim copies of the Program's source code as you receive it, in any medium, provided that you conspicuously and appropriately publish on each copy an appropriate copyright notice; keep intact all notices stating that this License and any non-permissive terms added in accord with section 7 apply to the code; keep intact all notices of the absence of any warranty; and give all recipients a copy of this License along with the Program.

You may charge any price or no price for each copy that you convey, and you may offer support or warranty protection for a fee.

5. Conveying Modified Source Versions.

You may convey a work based on the Program, or the modifications to produce it from the Program, in the form of source code under the terms of section 4, provided that you also meet all of these conditions:

  • a) The work must carry prominent notices stating that you modified it, and giving a relevant date.
  • b) The work must carry prominent notices stating that it is released under this License and any conditions added under section 7. This requirement modifies the requirement in section 4 to "keep intact all notices".
  • c) You must license the entire work, as a whole, under this License to anyone who comes into possession of a copy. This License will therefore apply, along with any applicable section 7 additional terms, to the whole of the work, and all its parts, regardless of how they are packaged. This License gives no permission to license the work in any other way, but it does not invalidate such permission if you have separately received it.
  • d) If the work has interactive user interfaces, each must display Appropriate Legal Notices; however, if the Program has interactive interfaces that do not display Appropriate Legal Notices, your work need not make them do so.

A compilation of a covered work with other separate and independent works, which are not by their nature extensions of the covered work, and which are not combined with it such as to form a larger program, in or on a volume of a storage or distribution medium, is called an "aggregate" if the compilation and its resulting copyright are not used to limit the access or legal rights of the compilation's users beyond what the individual works permit. Inclusion of a covered work in an aggregate does not cause this License to apply to the other parts of the aggregate.

6. Conveying Non-Source Forms.

You may convey a covered work in object code form under the terms of sections 4 and 5, provided that you also convey the machine-readable Corresponding Source under the terms of this License, in one of these ways:

  • a) Convey the object code in, or embodied in, a physical product (including a physical distribution medium), accompanied by the Corresponding Source fixed on a durable physical medium customarily used for software interchange.
  • b) Convey the object code in, or embodied in, a physical product (including a physical distribution medium), accompanied by a written offer, valid for at least three years and valid for as long as you offer spare parts or customer support for that product model, to give anyone who possesses the object code either (1) a copy of the Corresponding Source for all the software in the product that is covered by this License, on a durable physical medium customarily used for software interchange, for a price no more than your reasonable cost of physically performing this conveying of source, or (2) access to copy the Corresponding Source from a network server at no charge.
  • c) Convey individual copies of the object code with a copy of the written offer to provide the Corresponding Source. This alternative is allowed only occasionally and noncommercially, and only if you received the object code with such an offer, in accord with subsection 6b.
  • d) Convey the object code by offering access from a designated place (gratis or for a charge), and offer equivalent access to the Corresponding Source in the same way through the same place at no further charge. You need not require recipients to copy the Corresponding Source along with the object code. If the place to copy the object code is a network server, the Corresponding Source may be on a different server (operated by you or a third party) that supports equivalent copying facilities, provided you maintain clear directions next to the object code saying where to find the Corresponding Source. Regardless of what server hosts the Corresponding Source, you remain obligated to ensure that it is available for as long as needed to satisfy these requirements.
  • e) Convey the object code using peer-to-peer transmission, provided you inform other peers where the object code and Corresponding Source of the work are being offered to the general public at no charge under subsection 6d.

A separable portion of the object code, whose source code is excluded from the Corresponding Source as a System Library, need not be included in conveying the object code work.

A "User Product" is either (1) a "consumer product", which means any tangible personal property which is normally used for personal, family, or household purposes, or (2) anything designed or sold for incorporation into a dwelling. In determining whether a product is a consumer product, doubtful cases shall be resolved in favor of coverage. For a particular product received by a particular user, "normally used" refers to a typical or common use of that class of product, regardless of the status of the particular user or of the way in which the particular user actually uses, or expects or is expected to use, the product. A product is a consumer product regardless of whether the product has substantial commercial, industrial or non-consumer uses, unless such uses represent the only significant mode of use of the product.

"Installation Information" for a User Product means any methods, procedures, authorization keys, or other information required to install and execute modified versions of a covered work in that User Product from a modified version of its Corresponding Source. The information must suffice to ensure that the continued functioning of the modified object code is in no case prevented or interfered with solely because modification has been made.

If you convey an object code work under this section in, or with, or specifically for use in, a User Product, and the conveying occurs as part of a transaction in which the right of possession and use of the User Product is transferred to the recipient in perpetuity or for a fixed term (regardless of how the transaction is characterized), the Corresponding Source conveyed under this section must be accompanied by the Installation Information. But this requirement does not apply if neither you nor any third party retains the ability to install modified object code on the User Product (for example, the work has been installed in ROM).

The requirement to provide Installation Information does not include a requirement to continue to provide support service, warranty, or updates for a work that has been modified or installed by the recipient, or for the User Product in which it has been modified or installed. Access to a network may be denied when the modification itself materially and adversely affects the operation of the network or violates the rules and protocols for communication across the network.

Corresponding Source conveyed, and Installation Information provided, in accord with this section must be in a format that is publicly documented (and with an implementation available to the public in source code form), and must require no special password or key for unpacking, reading or copying.

7. Additional Terms.

"Additional permissions" are terms that supplement the terms of this License by making exceptions from one or more of its conditions. Additional permissions that are applicable to the entire Program shall be treated as though they were included in this License, to the extent that they are valid under applicable law. If additional permissions apply only to part of the Program, that part may be used separately under those permissions, but the entire Program remains governed by this License without regard to the additional permissions.

When you convey a copy of a covered work, you may at your option remove any additional permissions from that copy, or from any part of it. (Additional permissions may be written to require their own removal in certain cases when you modify the work.) You may place additional permissions on material, added by you to a covered work, for which you have or can give appropriate copyright permission.

Notwithstanding any other provision of this License, for material you add to a covered work, you may (if authorized by the copyright holders of that material) supplement the terms of this License with terms:

  • a) Disclaiming warranty or limiting liability differently from the terms of sections 15 and 16 of this License; or
  • b) Requiring preservation of specified reasonable legal notices or author attributions in that material or in the Appropriate Legal Notices displayed by works containing it; or
  • c) Prohibiting misrepresentation of the origin of that material, or requiring that modified versions of such material be marked in reasonable ways as different from the original version; or
  • d) Limiting the use for publicity purposes of names of licensors or authors of the material; or
  • e) Declining to grant rights under trademark law for use of some trade names, trademarks, or service marks; or
  • f) Requiring indemnification of licensors and authors of that material by anyone who conveys the material (or modified versions of it) with contractual assumptions of liability to the recipient, for any liability that these contractual assumptions directly impose on those licensors and authors.

All other non-permissive additional terms are considered "further restrictions" within the meaning of section 10. If the Program as you received it, or any part of it, contains a notice stating that it is governed by this License along with a term that is a further restriction, you may remove that term. If a license document contains a further restriction but permits relicensing or conveying under this License, you may add to a covered work material governed by the terms of that license document, provided that the further restriction does not survive such relicensing or conveying.

If you add terms to a covered work in accord with this section, you must place, in the relevant source files, a statement of the additional terms that apply to those files, or a notice indicating where to find the applicable terms.

Additional terms, permissive or non-permissive, may be stated in the form of a separately written license, or stated as exceptions; the above requirements apply either way.

8. Termination.

You may not propagate or modify a covered work except as expressly provided under this License. Any attempt otherwise to propagate or modify it is void, and will automatically terminate your rights under this License (including any patent licenses granted under the third paragraph of section 11).

However, if you cease all violation of this License, then your license from a particular copyright holder is reinstated (a) provisionally, unless and until the copyright holder explicitly and finally terminates your license, and (b) permanently, if the copyright holder fails to notify you of the violation by some reasonable means prior to 60 days after the cessation.

Moreover, your license from a particular copyright holder is reinstated permanently if the copyright holder notifies you of the violation by some reasonable means, this is the first time you have received notice of violation of this License (for any work) from that copyright holder, and you cure the violation prior to 30 days after your receipt of the notice.

Termination of your rights under this section does not terminate the licenses of parties who have received copies or rights from you under this License. If your rights have been terminated and not permanently reinstated, you do not qualify to receive new licenses for the same material under section 10.

9. Acceptance Not Required for Having Copies.

You are not required to accept this License in order to receive or run a copy of the Program. Ancillary propagation of a covered work occurring solely as a consequence of using peer-to-peer transmission to receive a copy likewise does not require acceptance. However, nothing other than this License grants you permission to propagate or modify any covered work. These actions infringe copyright if you do not accept this License. Therefore, by modifying or propagating a covered work, you indicate your acceptance of this License to do so.

10. Automatic Licensing of Downstream Recipients.

Each time you convey a covered work, the recipient automatically receives a license from the original licensors, to run, modify and propagate that work, subject to this License. You are not responsible for enforcing compliance by third parties with this License.

An "entity transaction" is a transaction transferring control of an organization, or substantially all assets of one, or subdividing an organization, or merging organizations. If propagation of a covered work results from an entity transaction, each party to that transaction who receives a copy of the work also receives whatever licenses to the work the party's predecessor in interest had or could give under the previous paragraph, plus a right to possession of the Corresponding Source of the work from the predecessor in interest, if the predecessor has it or can get it with reasonable efforts.

You may not impose any further restrictions on the exercise of the rights granted or affirmed under this License. For example, you may not impose a license fee, royalty, or other charge for exercise of rights granted under this License, and you may not initiate litigation (including a cross-claim or counterclaim in a lawsuit) alleging that any patent claim is infringed by making, using, selling, offering for sale, or importing the Program or any portion of it.

11. Patents.

A "contributor" is a copyright holder who authorizes use under this License of the Program or a work on which the Program is based. The work thus licensed is called the contributor's "contributor version".

A contributor's "essential patent claims" are all patent claims owned or controlled by the contributor, whether already acquired or hereafter acquired, that would be infringed by some manner, permitted by this License, of making, using, or selling its contributor version, but do not include claims that would be infringed only as a consequence of further modification of the contributor version. For purposes of this definition, "control" includes the right to grant patent sublicenses in a manner consistent with the requirements of this License.

Each contributor grants you a non-exclusive, worldwide, royalty-free patent license under the contributor's essential patent claims, to make, use, sell, offer for sale, import and otherwise run, modify and propagate the contents of its contributor version.

In the following three paragraphs, a "patent license" is any express agreement or commitment, however denominated, not to enforce a patent (such as an express permission to practice a patent or covenant not to sue for patent infringement). To "grant" such a patent license to a party means to make such an agreement or commitment not to enforce a patent against the party.

If you convey a covered work, knowingly relying on a patent license, and the Corresponding Source of the work is not available for anyone to copy, free of charge and under the terms of this License, through a publicly available network server or other readily accessible means, then you must either (1) cause the Corresponding Source to be so available, or (2) arrange to deprive yourself of the benefit of the patent license for this particular work, or (3) arrange, in a manner consistent with the requirements of this License, to extend the patent license to downstream recipients. "Knowingly relying" means you have actual knowledge that, but for the patent license, your conveying the covered work in a country, or your recipient's use of the covered work in a country, would infringe one or more identifiable patents in that country that you have reason to believe are valid.

If, pursuant to or in connection with a single transaction or arrangement, you convey, or propagate by procuring conveyance of, a covered work, and grant a patent license to some of the parties receiving the covered work authorizing them to use, propagate, modify or convey a specific copy of the covered work, then the patent license you grant is automatically extended to all recipients of the covered work and works based on it.

A patent license is "discriminatory" if it does not include within the scope of its coverage, prohibits the exercise of, or is conditioned on the non-exercise of one or more of the rights that are specifically granted under this License. You may not convey a covered work if you are a party to an arrangement with a third party that is in the business of distributing software, under which you make payment to the third party based on the extent of your activity of conveying the work, and under which the third party grants, to any of the parties who would receive the covered work from you, a discriminatory patent license (a) in connection with copies of the covered work conveyed by you (or copies made from those copies), or (b) primarily for and in connection with specific products or compilations that contain the covered work, unless you entered into that arrangement, or that patent license was granted, prior to 28 March 2007.

Nothing in this License shall be construed as excluding or limiting any implied license or other defenses to infringement that may otherwise be available to you under applicable patent law.

12. No Surrender of Others' Freedom.

If conditions are imposed on you (whether by court order, agreement or otherwise) that contradict the conditions of this License, they do not excuse you from the conditions of this License. If you cannot convey a covered work so as to satisfy simultaneously your obligations under this License and any other pertinent obligations, then as a consequence you may not convey it at all. For example, if you agree to terms that obligate you to collect a royalty for further conveying from those to whom you convey the Program, the only way you could satisfy both those terms and this License would be to refrain entirely from conveying the Program.

13. Use with the GNU Affero General Public License.

Notwithstanding any other provision of this License, you have permission to link or combine any covered work with a work licensed under version 3 of the GNU Affero General Public License into a single combined work, and to convey the resulting work. The terms of this License will continue to apply to the part which is the covered work, but the special requirements of the GNU Affero General Public License, section 13, concerning interaction through a network will apply to the combination as such.

14. Revised Versions of this License.

The Free Software Foundation may publish revised and/or new versions of the GNU General Public License from time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns.

Each version is given a distinguishing version number. If the Program specifies that a certain numbered version of the GNU General Public License "or any later version" applies to it, you have the option of following the terms and conditions either of that numbered version or of any later version published by the Free Software Foundation. If the Program does not specify a version number of the GNU General Public License, you may choose any version ever published by the Free Software Foundation.

If the Program specifies that a proxy can decide which future versions of the GNU General Public License can be used, that proxy's public statement of acceptance of a version permanently authorizes you to choose that version for the Program.

Later license versions may give you additional or different permissions. However, no additional obligations are imposed on any author or copyright holder as a result of your choosing to follow a later version.

15. Disclaimer of Warranty.


16. Limitation of Liability.


17. Interpretation of Sections 15 and 16.

If the disclaimer of warranty and limitation of liability provided above cannot be given local legal effect according to their terms, reviewing courts shall apply local law that most closely approximates an absolute waiver of all civil liability in connection with the Program, unless a warranty or assumption of liability accompanies a copy of the Program in return for a fee.


How to Apply These Terms to Your New Programs

If you develop a new program, and you want it to be of the greatest possible use to the public, the best way to achieve this is to make it free software which everyone can redistribute and change under these terms.

To do so, attach the following notices to the program. It is safest to attach them to the start of each source file to most effectively state the exclusion of warranty; and each file should have at least the "copyright" line and a pointer to where the full notice is found.

    <one line to give the program's name and a brief idea of what it does.>
    Copyright (C) <year>  <name of author>

    This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program.  If not, see <>.

Also add information on how to contact you by electronic and paper mail.

If the program does terminal interaction, make it output a short notice like this when it starts in an interactive mode:

    <program>  Copyright (C) <year>  <name of author>
    This program comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
    This is free software, and you are welcome to redistribute it
    under certain conditions; type `show c' for details.

The hypothetical commands `show w' and `show c' should show the appropriate parts of the General Public License. Of course, your program's commands might be different; for a GUI interface, you would use an "about box".

You should also get your employer (if you work as a programmer) or school, if any, to sign a "copyright disclaimer" for the program, if necessary. For more information on this, and how to apply and follow the GNU GPL, see

The GNU General Public License does not permit incorporating your program into proprietary programs. If your program is a subroutine library, you may consider it more useful to permit linking proprietary applications with the library. If this is what you want to do, use the GNU Lesser General Public License instead of this License. But first, please read

creative commons

Attribution 4.0 International

Creative Commons Corporation (“Creative Commons”) is not a law firm and does not provide legal services or legal advice. Distribution of Creative Commons public licenses does not create a lawyer-client or other relationship. Creative Commons makes its licenses and related information available on an “as-is” basis. Creative Commons gives no warranties regarding its licenses, any material licensed under their terms and conditions, or any related information. Creative Commons disclaims all liability for damages resulting from their use to the fullest extent possible.

Using Creative Commons Public Licenses

Creative Commons public licenses provide a standard set of terms and conditions that creators and other rights holders may use to share original works of authorship and other material subject to copyright and certain other rights specified in the public license below. The following considerations are for informational purposes only, are not exhaustive, and do not form part of our licenses.

  • Considerations for licensors: Our public licenses are intended for use by those authorized to give the public permission to use material in ways otherwise restricted by copyright and certain other rights. Our licenses are irrevocable. Licensors should read and understand the terms and conditions of the license they choose before applying it. Licensors should also secure all rights necessary before applying our licenses so that the public can reuse the material as expected. Licensors should clearly mark any material not subject to the license. This includes other CC-licensed material, or material used under an exception or limitation to copyright. More considerations for licensors.

  • Considerations for the public: By using one of our public licenses, a licensor grants the public permission to use the licensed material under specified terms and conditions. If the licensor’s permission is not necessary for any reason–for example, because of any applicable exception or limitation to copyright–then that use is not regulated by the license. Our licenses grant only permissions under copyright and certain other rights that a licensor has authority to grant. Use of the licensed material may still be restricted for other reasons, including because others have copyright or other rights in the material. A licensor may make special requests, such as asking that all changes be marked or described. Although not required by our licenses, you are encouraged to respect those requests where reasonable. More considerations for the public.

Creative Commons Attribution 4.0 International Public License

By exercising the Licensed Rights (defined below), You accept and agree to be bound by the terms and conditions of this Creative Commons Attribution 4.0 International Public License ("Public License"). To the extent this Public License may be interpreted as a contract, You are granted the Licensed Rights in consideration of Your acceptance of these terms and conditions, and the Licensor grants You such rights in consideration of benefits the Licensor receives from making the Licensed Material available under these terms and conditions.

Section 1 – Definitions.

a. Adapted Material means material subject to Copyright and Similar Rights that is derived from or based upon the Licensed Material and in which the Licensed Material is translated, altered, arranged, transformed, or otherwise modified in a manner requiring permission under the Copyright and Similar Rights held by the Licensor. For purposes of this Public License, where the Licensed Material is a musical work, performance, or sound recording, Adapted Material is always produced where the Licensed Material is synched in timed relation with a moving image.

b. Adapter's License means the license You apply to Your Copyright and Similar Rights in Your contributions to Adapted Material in accordance with the terms and conditions of this Public License.

c. Copyright and Similar Rights means copyright and/or similar rights closely related to copyright including, without limitation, performance, broadcast, sound recording, and Sui Generis Database Rights, without regard to how the rights are labeled or categorized. For purposes of this Public License, the rights specified in Section 2(b)(1)-(2) are not Copyright and Similar Rights.

d. Effective Technological Measures means those measures that, in the absence of proper authority, may not be circumvented under laws fulfilling obligations under Article 11 of the WIPO Copyright Treaty adopted on December 20, 1996, and/or similar international agreements.

e. Exceptions and Limitations means fair use, fair dealing, and/or any other exception or limitation to Copyright and Similar Rights that applies to Your use of the Licensed Material.

f. Licensed Material means the artistic or literary work, database, or other material to which the Licensor applied this Public License.

g. Licensed Rights means the rights granted to You subject to the terms and conditions of this Public License, which are limited to all Copyright and Similar Rights that apply to Your use of the Licensed Material and that the Licensor has authority to license.

h. Licensor means the individual(s) or entity(ies) granting rights under this Public License.

i. Share means to provide material to the public by any means or process that requires permission under the Licensed Rights, such as reproduction, public display, public performance, distribution, dissemination, communication, or importation, and to make material available to the public including in ways that members of the public may access the material from a place and at a time individually chosen by them.

j. Sui Generis Database Rights means rights other than copyright resulting from Directive 96/9/EC of the European Parliament and of the Council of 11 March 1996 on the legal protection of databases, as amended and/or succeeded, as well as other essentially equivalent rights anywhere in the world.

k. You means the individual or entity exercising the Licensed Rights under this Public License. Your has a corresponding meaning.

Section 2 – Scope.

a. License grant.

  1. Subject to the terms and conditions of this Public License, the Licensor hereby grants You a worldwide, royalty-free, non-sublicensable, non-exclusive, irrevocable license to exercise the Licensed Rights in the Licensed Material to:

    A. reproduce and Share the Licensed Material, in whole or in part; and

    B. produce, reproduce, and Share Adapted Material.

  2. Exceptions and Limitations. For the avoidance of doubt, where Exceptions and Limitations apply to Your use, this Public License does not apply, and You do not need to comply with its terms and conditions.

  3. Term. The term of this Public License is specified in Section 6(a).

  4. Media and formats; technical modifications allowed. The Licensor authorizes You to exercise the Licensed Rights in all media and formats whether now known or hereafter created, and to make technical modifications necessary to do so. The Licensor waives and/or agrees not to assert any right or authority to forbid You from making technical modifications necessary to exercise the Licensed Rights, including technical modifications necessary to circumvent Effective Technological Measures. For purposes of this Public License, simply making modifications authorized by this Section 2(a)(4) never produces Adapted Material.

  5. Downstream recipients.

    A. Offer from the Licensor – Licensed Material. Every recipient of the Licensed Material automatically receives an offer from the Licensor to exercise the Licensed Rights under the terms and conditions of this Public License.

    B. No downstream restrictions. You may not offer or impose any additional or different terms or conditions on, or apply any Effective Technological Measures to, the Licensed Material if doing so restricts exercise of the Licensed Rights by any recipient of the Licensed Material.

  6. No endorsement. Nothing in this Public License constitutes or may be construed as permission to assert or imply that You are, or that Your use of the Licensed Material is, connected with, or sponsored, endorsed, or granted official status by, the Licensor or others designated to receive attribution as provided in Section 3(a)(1)(A)(i).

b. Other rights.

  1. Moral rights, such as the right of integrity, are not licensed under this Public License, nor are publicity, privacy, and/or other similar personality rights; however, to the extent possible, the Licensor waives and/or agrees not to assert any such rights held by the Licensor to the limited extent necessary to allow You to exercise the Licensed Rights, but not otherwise.

  2. Patent and trademark rights are not licensed under this Public License.

  3. To the extent possible, the Licensor waives any right to collect royalties from You for the exercise of the Licensed Rights, whether directly or through a collecting society under any voluntary or waivable statutory or compulsory licensing scheme. In all other cases the Licensor expressly reserves any right to collect such royalties.

Section 3 – License Conditions.

Your exercise of the Licensed Rights is expressly made subject to the following conditions.

a. Attribution.

  1. If You Share the Licensed Material (including in modified form), You must:

    A. retain the following if it is supplied by the Licensor with the Licensed Material:

    i. identification of the creator(s) of the Licensed Material and any others designated to receive attribution, in any reasonable manner requested by the Licensor (including by pseudonym if designated);

    ii. a copyright notice;

    iii. a notice that refers to this Public License;

    iv. a notice that refers to the disclaimer of warranties;

    v. a URI or hyperlink to the Licensed Material to the extent reasonably practicable;

    B. indicate if You modified the Licensed Material and retain an indication of any previous modifications; and

    C. indicate the Licensed Material is licensed under this Public License, and include the text of, or the URI or hyperlink to, this Public License.

  2. You may satisfy the conditions in Section 3(a)(1) in any reasonable manner based on the medium, means, and context in which You Share the Licensed Material. For example, it may be reasonable to satisfy the conditions by providing a URI or hyperlink to a resource that includes the required information.

  3. If requested by the Licensor, You must remove any of the information required by Section 3(a)(1)(A) to the extent reasonably practicable.

  4. If You Share Adapted Material You produce, the Adapter's License You apply must not prevent recipients of the Adapted Material from complying with this Public License.

Section 4 – Sui Generis Database Rights.

Where the Licensed Rights include Sui Generis Database Rights that apply to Your use of the Licensed Material:

a. for the avoidance of doubt, Section 2(a)(1) grants You the right to extract, reuse, reproduce, and Share all or a substantial portion of the contents of the database;

b. if You include all or a substantial portion of the database contents in a database in which You have Sui Generis Database Rights, then the database in which You have Sui Generis Database Rights (but not its individual contents) is Adapted Material; and

c. You must comply with the conditions in Section 3(a) if You Share all or a substantial portion of the contents of the database.

For the avoidance of doubt, this Section 4 supplements and does not replace Your obligations under this Public License where the Licensed Rights include other Copyright and Similar Rights.

Section 5 – Disclaimer of Warranties and Limitation of Liability.

a. Unless otherwise separately undertaken by the Licensor, to the extent possible, the Licensor offers the Licensed Material as-is and as-available, and makes no representations or warranties of any kind concerning the Licensed Material, whether express, implied, statutory, or other. This includes, without limitation, warranties of title, merchantability, fitness for a particular purpose, non-infringement, absence of latent or other defects, accuracy, or the presence or absence of errors, whether or not known or discoverable. Where disclaimers of warranties are not allowed in full or in part, this disclaimer may not apply to You.

b. To the extent possible, in no event will the Licensor be liable to You on any legal theory (including, without limitation, negligence) or otherwise for any direct, special, indirect, incidental, consequential, punitive, exemplary, or other losses, costs, expenses, or damages arising out of this Public License or use of the Licensed Material, even if the Licensor has been advised of the possibility of such losses, costs, expenses, or damages. Where a limitation of liability is not allowed in full or in part, this limitation may not apply to You.

c. The disclaimer of warranties and limitation of liability provided above shall be interpreted in a manner that, to the extent possible, most closely approximates an absolute disclaimer and waiver of all liability.

Section 6 – Term and Termination.

a. This Public License applies for the term of the Copyright and Similar Rights licensed here. However, if You fail to comply with this Public License, then Your rights under this Public License terminate automatically.

b. Where Your right to use the Licensed Material has terminated under Section 6(a), it reinstates:

  1. automatically as of the date the violation is cured, provided it is cured within 30 days of Your discovery of the violation; or

  2. upon express reinstatement by the Licensor.

For the avoidance of doubt, this Section 6(b) does not affect any right the Licensor may have to seek remedies for Your violations of this Public License.

c. For the avoidance of doubt, the Licensor may also offer the Licensed Material under separate terms or conditions or stop distributing the Licensed Material at any time; however, doing so will not terminate this Public License.

d. Sections 1, 5, 6, 7, and 8 survive termination of this Public License.

Section 7 – Other Terms and Conditions.

a. The Licensor shall not be bound by any additional or different terms or conditions communicated by You unless expressly agreed.

b. Any arrangements, understandings, or agreements regarding the Licensed Material not stated herein are separate from and independent of the terms and conditions of this Public License.

Section 8 – Interpretation.

a. For the avoidance of doubt, this Public License does not, and shall not be interpreted to, reduce, limit, restrict, or impose conditions on any use of the Licensed Material that could lawfully be made without permission under this Public License.

b. To the extent possible, if any provision of this Public License is deemed unenforceable, it shall be automatically reformed to the minimum extent necessary to make it enforceable. If the provision cannot be reformed, it shall be severed from this Public License without affecting the enforceability of the remaining terms and conditions.

c. No term or condition of this Public License will be waived and no failure to comply consented to unless expressly agreed to by the Licensor.

d. Nothing in this Public License constitutes or may be interpreted as a limitation upon, or waiver of, any privileges and immunities that apply to the Licensor or You, including from the legal processes of any jurisdiction or authority.

Creative Commons is not a party to its public licenses. Notwithstanding, Creative Commons may elect to apply one of its public licenses to material it publishes and in those instances will be considered the “Licensor.” Except for the limited purpose of indicating that material is shared under a Creative Commons public license or as otherwise permitted by the Creative Commons policies published at, Creative Commons does not authorize the use of the trademark “Creative Commons” or any other trademark or logo of Creative Commons without its prior written consent including, without limitation, in connection with any unauthorized modifications to any of its public licenses or any other arrangements, understandings, or agreements concerning use of licensed material. For the avoidance of doubt, this paragraph does not form part of the public licenses.

Creative Commons may be contacted at