Welcome to Synapse

This document aims to get you started with contributing to this repo!

1. Who can contribute to Synapse?

Everyone is welcome to contribute code to projects, provided that they are willing to license their contributions under the same license as the project itself. We follow a simple 'inbound=outbound' model for contributions: the act of submitting an 'inbound' contribution means that the contributor agrees to license the code under the same terms as the project's overall 'outbound' license - in our case, this is almost always Apache Software License v2 (see LICENSE).

2. What do I need?

The code of Synapse is written in Python 3. To do pretty much anything, you'll need a recent version of Python 3.

The source code of Synapse is hosted on GitHub. You will also need a recent version of git.

For some tests, you will need a recent version of Docker.

3. Get the source.

The preferred and easiest way to contribute changes is to fork the relevant project on GitHub, and then create a pull request to ask us to pull your changes into our repo.

Please base your changes on the develop branch.

git clone
git checkout develop

If you need help getting started with git, this is beyond the scope of the document, but you can find many good git tutorials on the web.

4. Install the dependencies

Under Unix (macOS, Linux, BSD, ...)

Once you have installed Python 3 and added the source, please open a terminal and setup a virtualenv, as follows:

cd path/where/you/have/cloned/the/repository
python3 -m venv ./env
source ./env/bin/activate
pip install -e ".[all,lint,mypy,test]"
pip install tox

This will install the developer dependencies for the project.

Under Windows


5. Get in touch.

Join our developer community on Matrix: !

6. Pick an issue.

Fix your favorite problem or perhaps find a Good First Issue to work on.

7. Turn coffee and documentation into code and documentation!

Synapse's code style is documented here. Please follow it, including the conventions for the sample configuration file.

There is a growing amount of documentation located in the docs directory. This documentation is intended primarily for sysadmins running their own Synapse instance, as well as developers interacting externally with Synapse. docs/dev exists primarily to house documentation for Synapse developers. docs/admin_api houses documentation regarding Synapse's Admin API, which is used mostly by sysadmins and external service developers.

If you add new files added to either of these folders, please use GitHub-Flavoured Markdown.

Some documentation also exists in Synapse's GitHub Wiki, although this is primarily contributed to by community authors.

8. Test, test, test!

While you're developing and before submitting a patch, you'll want to test your code.

Run the linters.

The linters look at your code and do two things:

  • ensure that your code follows the coding style adopted by the project;
  • catch a number of errors in your code.

They're pretty fast, don't hesitate!

source ./env/bin/activate

Note that this script will modify your files to fix styling errors. Make sure that you have saved all your files.

If you wish to restrict the linters to only the files changed since the last commit (much faster!), you can instead run:

source ./env/bin/activate
./scripts-dev/ -d

Or if you know exactly which files you wish to lint, you can instead run:

source ./env/bin/activate
./scripts-dev/ path/to/ path/to/ path/to/folder

Run the unit tests.

The unit tests run parts of Synapse, including your changes, to see if anything was broken. They are slower than the linters but will typically catch more errors.

source ./env/bin/activate
trial tests

If you wish to only run some unit tests, you may specify another module instead of tests - or a test class or a method:

source ./env/bin/activate
trial tests.handlers.test_admin.ExfiltrateData.test_invite

If your tests fail, you may wish to look at the logs (the default log level is ERROR):

less _trial_temp/test.log

To increase the log level for the tests, set SYNAPSE_TEST_LOG_LEVEL:


Run the integration tests.

The integration tests are a more comprehensive suite of tests. They run a full version of Synapse, including your changes, to check if anything was broken. They are slower than the unit tests but will typically catch more errors.

The following command will let you run the integration test with the most common configuration:

$ docker run --rm -it -v /path/where/you/have/cloned/the/repository\:/src:ro -v /path/to/where/you/want/logs\:/logs matrixdotorg/sytest-synapse:py37

This configuration should generally cover your needs. For more details about other configurations, see documentation in the SyTest repo.

9. Submit your patch.

Once you're happy with your patch, it's time to prepare a Pull Request.

To prepare a Pull Request, please:

  1. verify that all the tests pass, including the coding style;
  2. sign off your contribution;
  3. git push your commit to your fork of Synapse;
  4. on GitHub, create the Pull Request;
  5. add a changelog entry and push it to your Pull Request;
  6. for most contributors, that's all - however, if you are a member of the organization matrix-org, on GitHub, please request a review from / Synapse Core.


All changes, even minor ones, need a corresponding changelog / newsfragment entry. These are managed by Towncrier.

To create a changelog entry, make a new file in the changelog.d directory named in the format of PRnumber.type. The type can be one of the following:

  • feature
  • bugfix
  • docker (for updates to the Docker image)
  • doc (for updates to the documentation)
  • removal (also used for deprecations)
  • misc (for internal-only changes)

This file will become part of our changelog at the next release, so the content of the file should be a short description of your change in the same style as the rest of the changelog. The file can contain Markdown formatting, and should end with a full stop (.) or an exclamation mark (!) for consistency.

Adding credits to the changelog is encouraged, we value your contributions and would like to have you shouted out in the release notes!

For example, a fix in PR #1234 would have its changelog entry in changelog.d/1234.bugfix, and contain content like:

The security levels of Florbs are now validated when received via the /federation/florb endpoint. Contributed by Jane Matrix.

If there are multiple pull requests involved in a single bugfix/feature/etc, then the content for each changelog.d file should be the same. Towncrier will merge the matching files together into a single changelog entry when we come to release.

How do I know what to call the changelog file before I create the PR?

Obviously, you don't know if you should call your newsfile 1234.bugfix or 5678.bugfix until you create the PR, which leads to a chicken-and-egg problem.

There are two options for solving this:

  1. Open the PR without a changelog file, see what number you got, and then add the changelog file to your branch (see Updating your pull request), or:

  2. Look at the list of all issues/PRs, add one to the highest number you see, and quickly open the PR before somebody else claims your number.

    This script might be helpful if you find yourself doing this a lot.

Sorry, we know it's a bit fiddly, but it's really helpful for us when we come to put together a release!

Debian changelog

Changes which affect the debian packaging files (in debian) are an exception to the rule that all changes require a changelog.d file.

In this case, you will need to add an entry to the debian changelog for the next release. For this, run the following command:


This will make up a new version number (if there isn't already an unreleased version in flight), and open an editor where you can add a new changelog entry. (Our release process will ensure that the version number and maintainer name is corrected for the release.)

If your change affects both the debian packaging and files outside the debian directory, you will need both a regular newsfragment and an entry in the debian changelog. (Though typically such changes should be submitted as two separate pull requests.)

Sign off

In order to have a concrete record that your contribution is intentional and you agree to license it under the same terms as the project's license, we've adopted the same lightweight approach that the Linux Kernel submitting patches process, Docker, and many other projects use: the DCO (Developer Certificate of Origin: This is a simple declaration that you wrote the contribution or otherwise have the right to contribute it to Matrix:

Developer Certificate of Origin
Version 1.1

Copyright (C) 2004, 2006 The Linux Foundation and its contributors.
660 York Street, Suite 102,
San Francisco, CA 94110 USA

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

Developer's Certificate of Origin 1.1

By making a contribution to this project, I certify that:

(a) The contribution was created in whole or in part by me and I
    have the right to submit it under the open source license
    indicated in the file; or

(b) The contribution is based upon previous work that, to the best
    of my knowledge, is covered under an appropriate open source
    license and I have the right under that license to submit that
    work with modifications, whether created in whole or in part
    by me, under the same open source license (unless I am
    permitted to submit under a different license), as indicated
    in the file; or

(c) The contribution was provided directly to me by some other
    person who certified (a), (b) or (c) and I have not modified

(d) I understand and agree that this project and the contribution
    are public and that a record of the contribution (including all
    personal information I submit with it, including my sign-off) is
    maintained indefinitely and may be redistributed consistent with
    this project or the open source license(s) involved.

If you agree to this for your contribution, then all that's needed is to include the line in your commit or pull request comment:

Signed-off-by: Your Name <>

We accept contributions under a legally identifiable name, such as your name on government documentation or common-law names (names claimed by legitimate usage or repute). Unfortunately, we cannot accept anonymous contributions at this time.

Git allows you to add this signoff automatically when using the -s flag to git commit, which uses the name and email set in your and git configs.

10. Turn feedback into better code.

Once the Pull Request is opened, you will see a few things:

  1. our automated CI (Continuous Integration) pipeline will run (again) the linters, the unit tests, the integration tests and more;
  2. one or more of the developers will take a look at your Pull Request and offer feedback.

From this point, you should:

  1. Look at the results of the CI pipeline.
    • If there is any error, fix the error.
  2. If a developer has requested changes, make these changes and let us know if it is ready for a developer to review again.
  3. Create a new commit with the changes.
    • Please do NOT overwrite the history. New commits make the reviewer's life easier.
    • Push this commits to your Pull Request.
  4. Back to 1.

Once both the CI and the developers are happy, the patch will be merged into Synapse and released shortly!

11. Find a new issue.

By now, you know the drill!

Notes for maintainers on merging PRs etc

There are some notes for those with commit access to the project on how we manage git here.


That's it! Matrix is a very open and collaborative project as you might expect given our obsession with open communication. If we're going to successfully matrix together all the fragmented communication technologies out there we are reliant on contributions and collaboration from the community to do so. So please get involved - and we hope you have as much fun hacking on Matrix as we do!