Creating CATMAID extensions

In the past, anyone wanting to extend CATMAID for their specific use case would need to fork the main repository, making it difficult to take advantage of future improvements to mainline CATMAID, and decreasing utility of the extension to people who may want to make use of it later. Therefore, we have designed the extension system to allow third parties to create external modules which interface with mainline CATMAID without having to change it.


CATMAID extensions are Django apps which form standalone python modules. When that module is made available to the python environment and added to INSTALLED_APPS in your local, Django can pick up any database models, API endpoints, and static files associated with the app, and code in the app can interact with code in mainline CATMAID. This modular approach allows much greater interoperability between different versions of CATMAID and the extension.

In the documentation below, we use a fictional extension called myextension.

Installing an Extension

  1. Install the app into your python environment, either by using pip install
    from PyPI, or cloning the repo and using pip to install from the local
  2. Let Django know you’ve installed it by adding
    INSTALLED_APPS += (myextension.apps.MyextensionConfig, ) (note the capital M and the comma!) to your
  3. Run python migrate to update the database as necessary. WARNING:
    it is possible for a migration to irreversibly change or delete data in your existing database.
  4. Run python collectstatic to pick up static files including
    stylesheets and frontend widgets.

API endpoints should be available at BASE_URL/ext/myextension/...

Creating an extension

  1. Decide on a name! We’ll use myextension here.
  2. Make a branch of CATMAID, adding "myextension" to KNOWN_EXTENSIONS in
    CATMAID/django/projects/ Make a pull request for this to be included in mainline CATMAID - until then, just use this branch for testing. This should be the only required change.
  3. Create a directory which will hold the module and repository-related cruft (we
    recommend naming it something obvious like CATMAID-myextension), navigate to it, and then create an empty django app with django-admin startapp myextension
  4. Add an appropriate README, LICENSE,, and so on
    as laid out in Django’s documentation, in CATMAID-myextension. The manifest and setup files are particularly important.
  5. If your extension includes javascript and/or stylesheets, create
    myextension/ to make Django Pipeline aware of them. See synapsesuggestor and CATMAID for how they interoperate.
  6. Develop away! For testing purposes, you will need to install
    the extension in your CATMAID environment - it’s convenient to use pip install -e to install the module in editable mode and python collectstatic -l. Don’t forget to add it to INSTALLED_APPS.

To quickstart development, you may find this cookiecutter template valuable: clbarnes/CATMAID-ext-cookiecutter.

Community Standards

  • See the contributing page.
  • Don’t write any migrations which will change data or database tables in the underlying
    CATMAID installation.
  • Be aware of CATMAID’s namespace - don’t add dependencies or tables which could cause
    name collisions.
  • As per Django’s guidelines, namespace all static files, templates and so on to your
    app - e.g. static files should be in a directory called myextension/static/myextension/<files>