Contributions are welcome, and they are greatly appreciated! Every little bit helps, and credit will always be given.

You can contribute in many ways:

Types of Contributions

Report Bugs

Report bugs at

If you are reporting a bug, please include:

  • Your operating system name and version.

  • Any details about your local setup that might be helpful in troubleshooting.

  • Detailed steps to reproduce the bug.

Fix Bugs

Look through the Github issues for bugs. If you want to start working on a bug then please write short message on the issue tracker to prevent duplicate work.

Implement Features

Look through the Github issues for features. If you want to start working on an issue then please write short message on the issue tracker to prevent duplicate work.

Contributing a new cluster or cloud execution backend

Execution backends are added by implementing a so-called Executor. All executors are located in snakemake/executors/. In order to implement a new executor, you have to inherit from the class ClusterExecutor. Below you find a skeleton

class SkeletonExecutor(ClusterExecutor):
    def __init__(self, workflow, dag, cores,

        super().__init__(workflow, dag, None,
                         assume_shared_fs=False, # if your executor relies on a shared file system, set this to True
                         max_status_checks_per_second=max_status_checks_per_second)  # set this to a reasonable default

        # add additional attributes

    def shutdown(self):
        # perform additional steps on shutdown if necessary

    def cancel(self):
        for job in self.active_jobs:
            # cancel active jobs here

    def run_jobs(self, jobs, callback=None, submit_callback=None, error_callback=None):
        """Run a list of jobs that is ready at a given point in time.

        By default, this method just runs each job individually.
        This behavior is inherited and therefore this method can be removed from the skeleton if the
        default behavior is intended.
        This method can be overwritten to submit many jobs in a more efficient way than one-by-one.

        Note that in any case, for each job, the callback functions have to be called individually!
        for job in jobs:

    def run(self, job,
        """Run an individual job or a job group.

        # Necessary: perform additional executor independent steps before running the job

        # obtain job execution command
        exec_job = self.format_job(
            self.exec_job, job, _quote_all=True,
            use_threads="--force-use-threads" if not job.is_group() else "")

        # submit job here, and obtain job ids from the backend

        # register job as active, using your own namedtuple.
        # The namedtuple must at least contain the attributes
        # job, jobid, callback, error_callback.
            job, jobid, callback, error_callback))

    async def _wait_for_jobs(self):
        from snakemake.executors import sleep
        # busy wait on job completion
        # This is only needed if your backend does not allow to use callbacks
        # for obtaining job status.
        while True:
            # always use self.lock to avoid race conditions
            async with async_lock(self.lock):
                if not self.wait:
                active_jobs = self.active_jobs
                self.active_jobs = list()
                still_running = list()
            for j in active_jobs:
                # use self.status_rate_limiter to avoid too many API calls.
                async with self.status_rate_limiter:

                    # Retrieve status of job j from your backend via j.jobid
                    # Handle completion and errors, calling either j.callback(j.job)
                    # or j.error_callback(j.job)
                    # In case of error, add job j to still_running.
            async with async_lock(self.lock):
            await sleep()

Write Documentation

Snakemake could always use more documentation, whether as part of the official vcfpy docs, in docstrings, or even on the web in blog posts, articles, and such.

Snakemake uses Sphinx for the user manual (that you are currently reading). See project_info-doc_guidelines on how the documentation reStructuredText is used.

Submit Feedback

The best way to send feedback is to file an issue at

If you are proposing a feature:

  • Explain in detail how it would work.

  • Keep the scope as narrow as possible, to make it easier to implement.

  • Remember that this is a volunteer-driven project, and that contributions are welcome :)

Pull Request Guidelines

To update the documentation, fix bugs or add new features you need to create a Pull Request . A PR is a change you make to your local copy of the code for us to review and potentially integrate into the code base.

To create a Pull Request you need to do these steps:

  1. Create a Github account.

  2. Fork the repository.

  3. Clone your fork locally.

  4. Go to the created snakemake folder with cd snakemake.

  5. Create a new branch with git checkout -b <descriptive_branch_name>.

  6. Make your changes to the code or documentation.

  7. Run git add . to add all the changed files to the commit (to see what files will be added you can run git add . --dry-run).

  8. To commit the added files use git commit. (This will open a command line editor to write a commit message. These should have a descriptive 80 line header, followed by an empty line, and then a description of what you did and why. To use your command line text editor of choice use (for example) export GIT_EDITOR=vim before running git commit).

  9. Now you can push your changes to your Github copy of Snakemake by running git push origin <descriptive_branch_name>.

  10. If you now go to the webpage for your Github copy of Snakemake you should see a link in the sidebar called “Create Pull Request”.

  11. Now you need to choose your PR from the menu and click the “Create pull request” button. Be sure to change the pull request target branch to <descriptive_branch_name>!

If you want to create more pull requests, first run git checkout main and then start at step 5. with a new branch name.

Feel free to ask questions about this if you want to contribute to Snakemake :)

Testing Guidelines

To ensure that you do not introduce bugs into Snakemake, you should test your code thouroughly.

To have integration tests run automatically when commiting code changes to Github, you need to sign up on and register a user.

The easiest way to run your development version of Snakemake is perhaps to go to the folder containing your local copy of Snakemake and call:

$ conda env create -f test-environment.yml -n snakemake-testing
$ conda activate snakemake-testing
$ pip install -e .

This will make your development version of Snakemake the one called when running snakemake. You do not need to run this command after each time you make code changes.

From the base snakemake folder you call pytest to run all the tests, or choose one specific test:

$ pytest
$ pytest tests/

If you introduce a new feature you should add a new test to the tests directory. See the folder for examples.

Documentation Guidelines

For the documentation, please adhere to the following guidelines:

  • Put each sentence on its own line, this makes tracking changes through Git SCM easier.

  • Provide hyperlink targets, at least for the first two section levels. For this, use the format <document_part>-<section_name>, e.g., project_info-doc_guidelines.

  • Use the section structure from below.

.. document_part-heading_1:

Heading 1

.. document_part-heading_2:

Heading 2

.. document_part-heading_3:

Heading 3

.. document_part-heading_4:

Heading 4

.. document_part-heading_5:

Heading 5

.. document_part-heading_6:

Heading 6

Documentation Setup

For building the documentation, you have to install the Sphinx. If you have already installed Conda, all you need to do is to create a Snakemake development environment via

$ git clone
$ cd snakemake
$ conda env create -f doc-environment.yml -n snakemake

Then, the docs can be built with

$ conda activate snakemake
$ cd docs
$ make html
$ make clean && make html  # force rebuild

Alternatively, you can use virtualenv. The following assumes you have a working Python 3 setup.

$ git clone
$ cd snakemake/docs
$ virtualenv -p python3 .venv
$ source .venv/bin/activate
$ pip install --upgrade -r requirements.txt

Afterwards, the docs can be built with

$ source .venv/bin/activate
$ make html  # rebuild for changed files only
$ make clean && make html  # force rebuild