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Automated checks on pyproject.toml powered by JSON Schema definitions


This project is experimental and under active development. Issue reports and contributions are very welcome.


With the approval of PEP 517 and PEP 518, the Python community shifted towards a strong focus on standardisation for packaging software, which allows more freedom when choosing tools during development and make sure packages created using different technologies can interoperate without the need for custom installation procedures.

This shift became even more clear when PEP 621 was also approved, as a standardised way of specifying project metadata and dependencies.

validate-pyproject was born in this context, with the mission of validating pyproject.toml files, and make sure they are compliant with the standards and PEPs. Behind the scenes, validate-pyproject relies on JSON Schema files, which, in turn, are also a standardised way of checking if a given data structure complies with a certain specification.


The easiest way of using validate-pyproject is via CLI. To get started, you need to install the package, which can be easily done using pipx:

$ pipx install 'validate-pyproject[all]'

Now you can use validate-pyproject as a command line tool:

# in you terminal
$ validate-pyproject --help
$ validate-pyproject path/to/your/pyproject.toml

You can also use validate-pyproject in your Python scripts or projects:

# in your python code
from validate_pyproject import api, errors

# let's assume that you have access to a `loads` function
# responsible for parsing a string representing the TOML file
# (you can check the `toml` or `tomli` projects for that)
pyproject_as_dict = loads(pyproject_toml_str)

# now we can use validate-pyproject
validator = api.Validator()

except errors.ValidationError as ex:
    print(f"Invalid Document: {ex.message}")

To do so, don’t forget to add it to your virtual environment or specify it as a project or library dependency.


When you install validate-pyproject[all], the packages tomli, packaging and trove-classifiers will be automatically pulled as dependencies. tomli is a lightweight parser for TOML, while packaging and trove-classifiers are used to validate aspects of PEP 621.

If you are only interested in using the Python API and wants to keep the dependencies minimal, you can also install validate-pyproject (without the [all] extra dependencies group).

If you don’t install trove-classifiers, validate-pyproject will try to download a list of valid classifiers directly from PyPI (to prevent that, set the environment variable NO_NETWORK or VALIDATE_PYPROJECT_NO_NETWORK).

On the other hand, if validate-pyproject cannot find a copy of packaging in your environment, the validation will fail.

More details about validate-pyproject and its Python API can be found in our docs, which includes a description of the used JSON schemas, instructions for using it in a pre-compiled way and information about extending the validation with your own plugins.


If you consider contributing to this project, have a look on our contribution guides.


validate-pyproject can be installed as a pre-commit hook:

  - repo:
    rev: main
      - id: validate-pyproject

By default, this pre-commit hook will only validate the pyproject.toml file at the root of the project repository. You can customize that by defining a custom regular expression pattern using the files parameter.


This project and its sister project ini2toml were initially created in the context of PyScaffold, with the purpose of helping migrating existing projects to PEP 621-style configuration when it is made available on setuptools. For details and usage information on PyScaffold see