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Contribution Guidelines

Developing on CTFd

Developing new code for CTFd is easy and fun! CTFd is organized into components which each serve a distinct purpose.

Core Routes/Controllers

The core routes are identified in blueprints in the main CTFd folder for user facing routes and in the CTFd/admin folder for the admin panel. These core routes are used to display theme content and render the main server response that the user will receive.

API Routes/Controllers

The API routes are implemented in the CTFd/api folder as seperate blueprints for each type of resource used in CTFd. Most behavior that manipulates data should be implemented at the API level and seperated by method and resource level. The most common API methods are GET, POST, PATCH, DELETE.


CTFd makes heavy usage of the SQLAlchemy ORM to access database contents. The core CTFd models are defined here. Plugins are however capable of adding their own models.

CTFd makes use of alembic and Flask-Migrate to perform database migrations between versions.

For information on how to perform a migration, please see Performing Migrations.


Schemas provide an abstraction layer on top of the database models for permissioning and filtering of data. Schemas and the API work together to make distinctions about what data to show users and what data a user can edit.


Jinja2 is used by the CTFd server to render HTML content with data. In some cases (i.e. JavaScript challenge rendering), Mozilla Nunjucks templates are used as a mostly compatible alternative. Any templates written in Nunjucks must still be compatible with Jinja2.

JavaScript & CSS

JavaScript & CSS are used to style the front end of CTFd.



Python code in CTFd is linted with ruff, isort, and black.

Javascript & CSS

JavaScript and CSS are linted with prettier.


The recommendation is to integrate all linters into your editor as your changes will fail to pass if the lint checks fail. See the Makefile for make lint



Python tests are run using pytest on Github Actions. To run the test suite locally you can run make test. By default tests run against sqlite but this can be configured by setting the TESTING_DATABASE_URL environment variable.

CTFd v3 is Python 3 only. CTFd v2 supported Python 2 and 3.

Tests are run in parallel with pytest-xdist and each test is run in isolation from other tests by creating it's own database and CTFd instance.


As of CTFd 3.6, CTFd supports translations when using the core-beta theme. Currently translations are managed with Crowdin. If you wish to fix or maintain a language translation please join at CTFd's public Crowdin page.

When managing translations directly in source code, they are managed with pybabel. The correct pybabel commands are written in CTFd's Makefile as follows:

  • make translations-init - add a new language (e.g. make translations-init lang=af)
  • make translations-extract - extract messages from the source code and create a POT file
  • make translations-update - update the existing PO files using the POT file
  • make translations-compile - compile the existing PO files into MO files

Tips & Tricks

Typically while developing CTFd, developers use the provided script or its make serve wrapper and access CTFd at http://localhost:4000.

Very often you will need to generate testing data so that you can exercise CTFd's behavior. The included script will insert randomized testing data into the CTFd database.

The script can be used to create a CTFd export on the command line.

The script can be used to load in a CTFd export on the command line.

If you need to wipe CTFd completely, you should:

  • delete the database (CTFd/ctfd.db by default)
  • empty the cache. By default it will be stored in the .data folder if Redis is unavailable
  • (optional) remove the contents of the CTFd/uploads folder