For Software Developers

Hail is an open-source project. We welcome contributions to the repository.


  • Java 8 JDK Note: it must be Java 8. Hail does not support versions 9+ due to our dependency on Spark.

  • The Python and non-pip installation requirements in Getting Started

  • If you are setting HAIL_COMPILE_NATIVES=1, then you need the LZ4 library header files. On Debian and Ubuntu machines run: apt-get install liblz4-dev.

Building Hail

The Hail source code is hosted on GitHub:

git clone
cd hail/hail

By default, Hail uses pre-compiled native libraries that are compatible with recent Mac OS X and Debian releases. If you’re not using one of these OSes, set the environment (or Make) variable HAIL_COMPILE_NATIVES to any value. This variable tells GNU Make to build the native libraries from source.

Build and install a wheel file from source with local-mode pyspark:


As above, but explicitly specifying the Scala and Spark versions:


Building the Docs and Website

Install build dependencies listed in the docs style guide.

Build without testing the documentation examples:

make hail-docs-no-test

Build while testing the documentation examples (significantly slower):

make hail-docs

Serve the built website on http://localhost:8000/

(cd build/www && python3 -m http.server)

Running the tests

Install development dependencies:

make install-dev-deps

A couple Hail tests compare to PLINK 1.9 (not PLINK 2.0 [ignore the confusing URL]):

Execute every Hail test using at most 8 parallel threads:

make -j8 test


Chat with the dev team on our Zulip chatroom or development forum if you have an idea for a contribution. We can help you determine if your project is a good candidate for merging.

Keep in mind the following principles when submitting a pull request:

  • A PR should focus on a single feature. Multiple features should be split into multiple PRs.

  • Before submitting your PR, you should rebase onto the latest main.

  • PRs must pass all tests before being merged. See the section above on Running the tests locally.

  • PRs require a review before being merged. We will assign someone from our dev team to review your PR.

  • When you make a PR, include a short message that describes the purpose of the PR and any necessary context for the changes you are making.

  • For user facing changes (new functions, etc), include “CHANGELOG” in the commit message or PR title. This helps identify what should be included in the change log when a new version is released.