Validating ``package.json``

Validating package.json

marshmallow can be used to validate configuration according to a schema. Below is a schema that could be used to validate package.json files. This example demonstrates the following features:

• Validation and deserialization using Schema.load <marshmallow.Schema.load>
• :doc:Custom fields <../custom_fields>
• Specifying deserialization keys using data_key
• Including unknown keys using unknown = INCLUDE

.. literalinclude:: ../../examples/package_json_example.py :language: python

Given the following package.json file...

.. literalinclude:: ../../examples/package.json :language: json

We can validate it using the above script.

.. code-block:: shell-session

$ uv run examples/package_json_example.py < examples/package.json
{'description': 'The Pythonic JavaScript toolkit',
'dev_dependencies': {'pest': '^23.4.1'},
'license': 'MIT',
'main': 'index.js',
'name': 'dunderscore',
'scripts': {'test': 'pest'},
'version': <Version('1.2.3')>}

Notice that our custom field deserialized the version string to a Version object.

But if we pass an invalid package.json file...

.. literalinclude:: ../../examples/invalid_package.json :language: json

We see the corresponding error messages.

.. code-block:: shell-session

$ uv run examples/package_json_example.py < examples/invalid_package.json
ERROR: package.json is invalid
{'homepage': ['Not a valid URL.'], 'version': ['Not a valid version.']}