Contributing to Puma

By participating in this project, you agree to follow the code of conduct.

There are lots of ways to contribute to Puma. Some examples include:

Newbies welcome! We would be happy to help you make your first contribution to a F/OSS project.


Any questions about contributing may be asked in our Discussions.

If you're nervous, get stuck, need help, or want to know where to start and where you can help, please don't hesitate to book 30 minutes with maintainer @nateberkopec here. He is happy to help!

Nate also gave a 40 minute conference talk in 2022 detailing how Puma works, a brief overview of its internals, and a quick guide on how to contribute.

Clone the repo

Clone the Puma repository:

git clone git@github.com:puma/puma.git && cd puma


You need to install ragel to generate Puma's extension code.


brew install ragel


apt-get install ragel

Windows (Ruby 2.5 and later):

ridk exec pacman -S mingw-w64-x86_64-openssl mingw-w64-x86_64-ragel

Install Ruby dependencies

Install the Ruby dependencies:

bundle install

Compile the native extensions

To run Puma locally, you must compile the native extension. Running the test rake task does this automatically, but you may need to manually run the compile command if you want to run Puma and haven't run the tests yet:

Ubuntu, macOS, etc:

bundle exec rake compile


bundle exec rake -rdevkit compile

Run your local Puma

Now, you should be able to run Puma locally:

bundle exec bin/puma test/rackup/hello.ru
# -or-
bundle exec ruby -Ilib bin/puma test/rackup/hello.ru

Alternatively, you can reference your local copy in a project's Gemfile:

gem "puma", path: "/path/to/local/puma"

See the Bundler docs for more details.

Running tests

To run rubocop + tests:

bundle exec rake 

To run the test suite only:

bundle exec rake test

To run a single test file:

bundle exec ruby test/test_binder.rb

You can also run tests with m:

bundle exec m test/test_binder.rb

To run a single test:

bundle exec m test/test_binder.rb:37

To run a single test with 5 seconds as the test case timeout:

TEST_CASE_TIMEOUT=5 bundle exec m test/test_binder.rb:37

If you would like more information about extension building, SSL versions, your local Ruby version, and more, use the PUMA_TEST_DEBUG env variable:

PUMA_TEST_DEBUG=1 bundle exec rake test

File limits

Puma's test suite opens up a lot of sockets. This may exceed the default limit of your operating system. If your file limits are low, you may experience "too many open file" errors when running the Puma test suite.

# check your file limit
ulimit -S -n

# change file limit for the current session
ulimit -S -n <value>

We find that values of 4000 or more work well. Learn more about your file limits and how to change them here.

How to contribute

Puma could use your help in several areas!

Don't worry about "claiming an issue". No issues are "claimed" in Puma. Just start working on it. The issue tracker is almost always kept updated, so if there is an open issue, it is ready for you to contribute (unless you have questions about how to close issue - then please ask!). Once you have a few lines of code, post a draft PR. We are more than happy to help once you have a draft PR up.

New to systems programming? That's ok! Puma deals with concepts you may not have been familiar with before, like sockets, TCP, UDP, SSL, and Threads. That's ok! You can learn by contributing. Also, see the "Bibliography" section at the end of this document.

The contrib-wanted label indicates that an issue might approachable to first-time contributors.

Reproducing bug reports: The needs-repro label indicates than an issue lacks reproduction steps. You can help by reproducing the issue and sharing the steps you took in the comments.

Helping with our native extensions: If you are interested in writing C or Java, we could really use your help. Check out the issue labels for c-ext and JRuby.

Fixing bugs: Issues with the bug label have working reproduction steps, which you can use to write a test and submit a patch.

Writing features: The feature label highlights requests for new functionality. Write tests and code up our new feature!

Code review: Take a look at open pull requests and offer your feedback. Code review is not just for maintainers. We need your help and eyeballs!

Write documentation: Puma needs more docs in many areas, especially where we have open issues with the docs label.

Reproduction steps

Reproducing a bug helps identify the root cause of that bug so it can be fixed.

To get started, create a rackup file and config file and then run your test app with:

bundle exec puma -C <path/to/config.rb> <path/to/rackup.ru>

For example, using a test rack app (test/rackup/hello.ru) and a test config file (test/config/settings.rb):

bundle exec puma -C test/config/settings.rb test/rackup/hello.ru

There is also a Dockerfile available for reproducing Linux-specific issues:

docker build -f tools/Dockerfile -t puma .
docker run -p 9292:9292 -it puma

Pull requests

Please open draft PRs as soon as you are ready for feedback from the community.

Code contributions should generally include test coverage. If you aren't sure how to test your changes, please open a pull request and leave a comment asking for help.

There's no need to update the changelog (History.md); that is done when a new release is made.

Puma uses GitHub Actions for CI testing. Please consider running the workflows in your fork before creating a PR. It is possible to enable GitHub Actions on your fork in the repositories' Actions tab.


Puma does not have a backport "policy" - maintainers will not consistently backport bugfixes to previous minor or major versions (we do treat security differently, see SECURITY.md.

As a contributor, you may make pull requests against -stable branches to backport fixes, and maintainers will release them once they're merged. For example, if you'd like to make a backport for 4.3.x, you can make a pull request against 4-3-stable. If there is no appropriate branch for the release you'd like to backport against, please just open an issue and we'll make one for you.

Join the community

If you're looking to contribute to Puma, please join us in Discussions.


Puma can be a bit intimidating for your first contribution because there's a lot of concepts here that you've probably never had to think about before - Rack, sockets, forking, threads etc. Here are some helpful links for learning more about things related to Puma: