jsonschema is an implementation of JSON Schema for Python (supporting 2.7+ including Python 3).

>>> from jsonschema import validate

>>> # A sample schema, like what we'd get from json.load()
>>> schema = {
...     "type" : "object",
...     "properties" : {
...         "price" : {"type" : "number"},
...         "name" : {"type" : "string"},
...     },
... }

>>> # If no exception is raised by validate(), the instance is valid.
>>> validate({"name" : "Eggs", "price" : 34.99}, schema)

>>> validate(
...     {"name" : "Eggs", "price" : "Invalid"}, schema
... )                                   # doctest: +IGNORE_EXCEPTION_DETAIL
Traceback (most recent call last):
    ...
ValidationError: 'Invalid' is not of type 'number'

It can also be used from console:

$ jsonschema -i sample.json sample.schema

• Full support for Draft 3 and Draft 4 of the schema.
• Lazy validation that can iteratively report all validation errors.
• Small and extensible
• Programmatic querying of which properties or items failed validation.

Version 2.6.0 drops support for Python 2.6.X (ha ha) and contains a number of small improvements in error messages, as well as a bug fix for ErrorTree.

If you have tox installed (perhaps via pip install tox or your package manager), running tox in the directory of your source checkout will run jsonschema's test suite on all of the versions of Python jsonschema supports. Note that you'll need to have all of those versions installed in order to run the tests on each of them, otherwise tox will skip (and fail) the tests on that version.

Of course you're also free to just run the tests on a single version with your favorite test runner. The tests live in the jsonschema.tests package.

jsonschema's benchmarks make use of perf.

Running them can be done via tox -e perf, or by invoking the perf commands externally (after ensuring that both it and jsonschema itself are installed):

$ python -m perf jsonschema/benchmarks/test_suite.py --hist --output results.json

To compare to a previous run, use:

$ python -m perf compare_to --table reference.json results.json

See the perf documentation for more details.

There's a mailing list for this implementation on Google Groups.

Please join, and feel free to send questions there.

I'm Julian Berman.

jsonschema is on GitHub.

Get in touch, via GitHub or otherwise, if you've got something to contribute, it'd be most welcome!

You can also generally find me on Freenode (nick: tos9) in various channels, including #python.

If you feel overwhelmingly grateful, you can woo me with beer money on Gittip or via Google Wallet with the email in my GitHub profile.