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Validation library and CLI tool for checking on 'pyproject.toml' files using JSON Schema

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Automated checks on pyproject.toml powered by JSON Schema definitions


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.

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.


The validate-pyproject-schema-store plugin has a vendored copy of pyproject.toml related SchemaStore entries. You can even install this using the [store] extra:

$ pipx install ‘validate-pyproject[all,store]’

Some of the tools in SchemaStore also have integrated validate-pyproject plugins, like cibuildwheel and scikit-build-core. However, unless you want to pin an exact version of those tools, the SchemaStore copy is lighter weight than installing the entire package.

If you want to write a custom plugin for your tool, please consider also contributing a copy to SchemaStore.


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

  - repo:
    rev: <insert current version here>
      - id: validate-pyproject
      # Optional extra validations from SchemaStore:
      additional_dependencies: ["validate-pyproject-schema-store[all]"]

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.

You can also use pre-commit autoupdate to update to the latest stable version of validate-pyproject (recommended).

You can also use validate-pyproject-schema-store as a pre-commit hook, which allows pre-commit to pin and update that instead of validate-pyproject itself.


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

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