Tutorial: How to become REUSE-compliant

This tutorial explains the basic methods of how to make a software project REUSE-compliant. By the end of this document, all your files will clearly have their copyright and licensing marked, and you will be able to verify this using the REUSE helper tool.

Making your project REUSE-compliant can be done in three simple steps:

  1. Choose and provide licenses
  2. Add copyright and license information to each file
  3. Confirm REUSE compliance

For the purpose of this tutorial, we will assume that the directory of your project looks like this:

project/
├── img/
│   ├── cat.jpg
│   └── dog.jpg
├── src/
│   └── main.c
├── .gitignore
├── Makefile
└── README.md

If you would like to reproduce the steps in this tutorial on your own computer, you can clone the example repository. The branch noncompliant matches the structure above, while the main branch is the successful result of this repository.

For each of these steps, you will first learn how to achieve them manually. However, the REUSE helper tool supports you with most tasks, and the necessary commands will be listed as well in the collapsible boxes. We recommend to first understand the basic principle before just executing the tool’s commands.

1. Choose and provide licenses

The first thing you need to do is to choose a license. For this tutorial, we assume that you chose the GNU General Public License (GPL) v3.0 or any later version. More than simply choosing a license, you need to put the license in your project directory.

You find your license in the SPDX License List. SPDX is an open standard for communicating license and copyright information. Each license is uniquely identified by a shortform SPDX License Identifier. The SPDX License Identifier for your chosen license is GPL-3.0-or-later.

You create a LICENSES directory in your project root which will contain all the licenses that you use in your project. You then download your license from the license-list-data repository and put it in the LICENSES directory. The name of the license should be its SPDX License Identifier followed by a file extension (in this example, GPL-3.0-or-later.txt).

You can initialise your project using reuse init. In an interactive dialogue you can define certain properties of your project and also one or multiple licenses. At the end, these licenses will be automatically downloaded to the correct location.

The reuse download command enables you to download a specific license. reuse download GPL-3.0-or-later would fulfil the task described in the manual instructions above. Running reuse download --all automatically downloads all licenses which the REUSE helper tool detects as being used in your project.

2. Add copyright and licensing information to each file

Now that you have a license, you need to indicate in the relevant files that these files fall under that license. You edit the comment header of src/main.c as such:

/*
 * SPDX-FileCopyrightText: 2019 Jane Doe <jane@example.com>
 *
 * SPDX-License-Identifier: GPL-3.0-or-later
 */

The SPDX-FileCopyrightText tag records the publication years and copyright holder of the contents of the file. You can read more about which publication years to use and what copyright holders are in the FAQ.

The SPDX-License-Identifier tag is followed by a valid SPDX License Expression, typically just the SPDX License Identifier of the license.

Each file must always contain these two tags in the header. You are allowed to use the tags multiple times if you have multiple copyright holders or licenses.

In the example project, you also edit Makefile and README.md using this header information, but of course with corresponding comment syntax.

The reuse addheader command helps with adding licensing and copyright information to your files. For the task above, the following command would do the job:

reuse addheader --copyright="Jane Doe <jane@example.com>" --license="GPL-3.0-or-later" src/main.c Makefile README.md

Please see the tool’s documentation about addheader for more options like comment styles and templates

Binary and uncommentable files

You also want to license your image files under GPL-3.0-or-later. Unfortunately, images and other binary files do not have comment headers that one can easily edit. Other examples include automatically generated files and certain data and configuration files for which comments are non-trivial.

There is a simple trick to circumvent this. Create the files cat.jpg.license and dog.jpg.license, each containing the same information about license and copyright holder as above.

The REUSE helper tool should automatically detect binary files and therefore automatically create a corresponding .license file.

If it does not, or if you would like to enforce this, add the --force-dot-license argument to the addheader command. So the command for the above task may look like this:

reuse addheader --copyright="Jane Doe <jane@example.com>" --license="GPL-3.0-or-later" --force-dot-license img/cat.jpg img/dog.jpg

Change licensing information

You discover that the photos of the cat and the dog were not licensed under the GPL at all, but under Creative Commons Attribution 4.0 International, owned by Max Mehl.

The SPDX License Identifier of this license is CC-BY-4.0. You create the file LICENSES/CC-BY-4.0.txt, following the same steps you used for GPL-3.0-or-later.

You then edit cat.jpg.license and dog.jpg.license to say:

SPDX-FileCopyrightText: 2019 Max Mehl <max.mehl@fsfe.org>

SPDX-License-Identifier: CC-BY-4.0

The tool as of now does not provide a way to replace existing REUSE-compliant copyright and licensing information. A run of the addheader command would not replace but extend the .license files with two additional lines stating the copyright of Max Mehl and the CC-BY-4.0 license. So you would have to update these manually.

However, the download command afterwards would allow you to download the new license automatically, so either with reuse download CC-BY-4.0 or simply reuse download --all.

Build artifacts

When you compile your program, you generate some build artifacts, such as src/main.o. You do not need to provide any licensing information for those files. Just use your .gitignore file to ignore these build artifacts. The REUSE tool will respect the contents of .gitignore.

Insignificant files

You probably will have files in your project that you do not find particularly copyrightable, for example configuration files such as .gitignore. Intuitively you may not want to license these files, but the fundamental idea of REUSE is that all your files will clearly have their copyright and licensing marked.

If you do not exercise any copyright over this file, you can use the CC0 license. This is functionally identical to putting the file in the public domain. Edit the file to contain:

# SPDX-FileCopyrightText: 2019 Jane Doe <jane@example.com>
#
# SPDX-License-Identifier: CC0-1.0

Consequently, you will have to provide the CC0-1.0 license in the LICENSES/ directory as well, just like the GPL-3.0-or-later and CC-BY-4.0 before.

More information about copyrightable files can be found in the REUSE FAQ.

As before, a combination of the addheader and download commands will fulfil the above step:

reuse addheader --copyright="Jane Doe <jane@example.com>" --license="CC0-1.0" .gitignore

reuse download --all

Result

Your project tree will now look like this:

project/
├── img/
│   ├── cat.jpg
│   ├── cat.jpg.license
│   ├── dog.jpg
│   └── dog.jpg.license
├── LICENSES/
│   ├── CC0-1.0.txt
│   ├── CC-BY-4.0.txt
│   └── GPL-3.0-or-later.txt
├── src/
│   └── main.c
├── .gitignore
├── Makefile
└── README.md

3. Confirm REUSE compliance

Now that you have marked all files with their copyright and licensing, it is time to check whether you did not miss anything. To do this, we provide a helper tool for you to use. You can read the full documentation, or read the quick steps below.

Follow the installation instructions available for multiple platforms. Now go to the project directory and run the linter.

$ cd path/to/project/
$ reuse lint
# SUMMARY

* Bad licenses:
* Deprecated licenses:
* Licenses without file extension:
* Missing licenses:
* Unused licenses:
* Used licenses: CC-BY-4.0, CC0-1.0, GPL-3.0-or-later
* Read errors: 0
* Files with copyright information: 6 / 6
* Files with license information: 6 / 6

Congratulations! Your project is compliant with version 3.0 of the REUSE Specification :-)

As you can see in the last line, the tool confirms that your project is compliant with REUSE now! To learn what the different sections mean, please have a look at the documentation of the lint command.

Getting help

After going through this tutorial, you understood REUSE and the three basic steps to properly license your software project – well done! But although we have covered a few edge cases, you might run into more questions soon. But don’t worry, we are here to help!:

If none of the links above were able to answer your question, please contact us by:

  • opening an issue on reuse-website for questions on the tutorial, FAQ or specification;

  • opening an issue on reuse-tool for questions on the REUSE tool;

  • or sending an email to the FSFE. Please note that we would prefer issues because they are publicly searchable for other people.

Thank you for your valuable contribution towards making software reusable!