Contributing to Black

Welcome! Happy to see you willing to make the project better. Have you read the entire user documentation yet?

Bird’s eye view

In terms of inspiration, Black is about as configurable as gofmt. This is deliberate.

Bug reports and fixes are always welcome! Please follow the issue template on GitHub for best results.

Before you suggest a new feature or configuration knob, ask yourself why you want it. If it enables better integration with some workflow, fixes an inconsistency, speeds things up, and so on - go for it! On the other hand, if your answer is “because I don’t like a particular formatting” then you’re not ready to embrace Black yet. Such changes are unlikely to get accepted. You can still try but prepare to be disappointed.


Development on the latest version of Python is preferred. As of this writing it’s 3.9. You can use any operating system. I am using macOS myself and CentOS at work.

Install all development dependencies using:

$ pipenv install --dev
$ pipenv shell
$ pre-commit install

If you haven’t used pipenv before but are comfortable with virtualenvs, just run pip install pipenv in the virtualenv you’re already using and invoke the command above from the cloned Black repo. It will do the correct thing.

Non pipenv install works too:

$ pip install -r test_requirements
$ pip install -e .[d]

Before submitting pull requests, run lints and tests with the following commands from the root of the black repo:

# Linting
$ pre-commit run -a

# Unit tests
$ tox -e py

# Optional Fuzz testing
$ tox -e fuzz

# Optional CI run to test your changes on many popular python projects
$ black-primer [-k -w /tmp/black_test_repos]

Docs Testing

If you make changes to docs, you can test they still build locally too.

$ pip install -r docs/requirements.txt
$ pip install [-e] .[d]
$ sphinx-build -a -b html -W docs/ docs/_build/


black-primer is used by CI to pull down well-known Black formatted projects and see if we get source code changes. It will error on formatting changes or errors. Please run before pushing your PR to see if you get the actions you would expect from Black with your PR. You may need to change primer.json configuration for it to pass.

For more black-primer information visit the documentation.


If you’re fixing a bug, add a test. Run it first to confirm it fails, then fix the bug, run it again to confirm it’s really fixed.

If adding a new feature, add a test. In fact, always add a test. But wait, before adding any large feature, first open an issue for us to discuss the idea first.


Thanks again for your interest in improving the project! You’re taking action when most people decide to sit and watch.