Code contributions

In order to expedite the contribution of code to the OME project, whether individual files or entire modules such as a service or web application, we have put together the following guidelines. If you have issues with any of the below, please let us know.

File headers

The official header templates for each file type (Java, Python, HTML, etc.) can be found in the docs/headers.txt file of the source repository. The correct template should be applied at the top of all newly created files. The header of existing files should not be modified without previous discussion except with regard to keeping the year line up to date, for example changing “2008-2011” to “2008-2013”.

Character encoding

OME Python and Java source files are all encoded in UTF-8.

Code style and linting

Code styling can be a matter of intense debate. We are in the process of introducing auto-formatters to most of our repositories to reduce the time wasted on formatting code or discussing code styles. Where possible pre-commit is used to manage auto-formatters such as black (Python), as well as linters such as flake8 (Python).


The copyright line for a newly created file is based on the institution of the creator of the file and will remain unchanged even if copied or moved. Before redistribution of code can take place, an agreement must be reached between the OME team and the copyright holder.


The licenses of any files intended for redistribution with OME must be compatible with the GPL and more restrictively for the web components with the AGPL. Some files in the code-base (the schema, etc.) are released under more liberal licenses but are still compatible with the GPL.


For a block of work to be considered for redistribution with OME, the code must further be made available in one of the following formats.

Patches/Pull requests

Smaller changes to the existing code base can be submitted to the team either as patches, or preferably as pull requests on GitHub. You can read more about pull requests on the Using Git page. The idea is that such smaller changes are reviewed line-by-line and then maintained by the core team.


Larger submissions, which cannot be effectively reviewed so intensively, should be submitted as git submodules. Such submodules provide a unique way to describe to a component version, which becomes linked into the main codebase. During checkout, all submodules are downloaded into the OME directory; and during the build process, submodules are compiled into the official distribution.

The OME team cannot maintain or ship code which is only available as a long-living branch (a fork) of the code base, and we would encourage submitters to use one of the above methods.

Procedure for accepting code contributions

External contributors will need to sign our Contributor License Agreement in order to get their pull requests reviewed.

External pull requests will get an initial review to identify if they are suitable to pass into our continuous integration system for building and testing. We try to do this within 2 days of submission but please be patient if we are busy and it takes longer.

If there are any obvious issues, we will comment and wait for you to fix them. Once we are confident the PR contains no obvious errors, an “include” label will be added which means the PR will be included in the merge build jobs for the appropriate branch.

Build failures will then be noted on the PR and we will either submit a patch or provide sufficient information for you to fix the problem yourself. The “include” label will be removed until this is completed. The PR will be merged once all the builds are green with the “include” label added.

If the code you wish to submit is large enough to require its own submodule, you should contact us to discuss how we might incorporate your work into the official distribution.

Examples of contribution templates

There are any number of other projects which have set up similar practices for code contributions. If you would like to read more on the rationale, please see:

See also

Best practices for git commit message formatting

Wikipedia article on Technical debt

Benefits of using an auto-formatter to avoid debates on style