An(other) implementation of JSON Schema (Draft 3) for Python
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jsonschema is an implementation of JSON Schema (currently in Draft 3) for Python (supporting 2.6+ 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'


  • Support for Draft 3 of the Schema with the exception of

    • $ref, and extends that use $refs
  • Lazy validation that can iteratively report all validation errors.

>>> from jsonschema import Validator
>>> schema = {
...     "type" : "array",
...     "items" : {"enum" : [1, 2, 3]},
...     "maxItems" : 2,
... }
>>> v = Validator()
>>> for error in sorted(v.iter_errors([2, 3, 4], schema), key=str):
...     print(error)
4 is not one of [1, 2, 3]
[2, 3, 4] is too long
  • Small and extensible
  • Programmatic querying of which properties or items failed validation.
>>> from jsonschema import ErrorTree, Validator
>>> schema = {
...     "type" : "array",
...     "items" : {"type" : "number", "enum" : [1, 2, 3]},
...     "minItems" : 3,
... }
>>> instance = ["spam", 2]
>>> v = Validator()
>>> tree = ErrorTree(v.iter_errors(instance, schema))

>>> sorted(tree.errors)

>>> 0 in tree

>>> 1 in tree

>>> sorted(tree[0].errors)
['enum', 'type']

>>> print(tree[0].errors["type"].message)
'spam' is not of type 'number'

Schema Versioning

JSON Schema is, at the time of this writing, seemingly at Draft 3, with preparations for Draft 4 underway. The Validator class and validate function take a version argument that you can use to specify what version of the Schema you are validating under.

As of right now, Draft 3 (jsonschema.DRAFT_3) is the only supported version, and the default when validating. Whether it will remain the default version in the future when it is superceeded is undecided, so if you want to be safe, explicitly declare which version to use when validating.

Release Notes

v0.5 is mostly just a bugfix release to fix a lingering bug for error objects' reqired properties (Issue #17) and for multiple types' validation for non-objects (Issue #18).

All of the deprecated parameters from v0.4 have also been removed in this release.

Running the Test Suite

jsonschema uses the wonderful Tox for its test suite. (It really is wonderful, if for some reason you haven't heard of it, you really should use it for your projects).

Assuming you have tox installed (perhaps via pip install tox or your package manager), just run tox in the directory of your source checkout to 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.


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.