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Projects are located in the projects folder of a Polylith workspace. Each project has its own pyproject.toml, where the project-specific dependencies are defined.

Bricks (your Python code)

Bricks are added to the packages section of [tool.poetry] or the [], described in Projects & pyproject.toml.

To keep a project up-to-date with needed bricks, there is a poly sync command available. Usage is described in commands. The command is there for convenience, you can also add the bricks manually.

Libraries (third-party dependencies)

The recommended workflow for Polylith is to use poetry add, or manually adding, to install the needed libraries to the Development pyproject.toml. The Development pyproject.toml is located at the Workspace root. The Development environment should have all dependencies added: all bricks and all the third-party libraries. The dev-dependencies (such as Mypy, Black, Flake8, Ruff etc.) are also added to the Development pyproject.toml.

A Project should only include the dependencies that are needed for it to run in a production environment.

Libraries are added separately into the project-specific pyproject.toml (pick the depencencies based on what's already in Development). The Python tools for the Polylith Architecture has a keep-things-simple approach to dependencies: just copy the needed dependencies from the development project, or use poetry add into a project.

Use the poly libs and/or poly check command to verify all that all dependencies have been added.

Both commands support the --directory option (coming from Poetry). This means that you can run the commands from the workspace root, but for a specific project:


poetry poly check --directory projects/my-project


hatch run poly check --directory projects/my-project


pdm run poly check --directory projects/my-project


rye run poly check --directory projects/my-project