lightweight-schema /

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jsonschema is a full featured validator for the JSON Schema specification. It conforms to the JSON Schema Proposal Second Draft which can be found at the following url:


jsonschema uses setup tools so it can be installed normally using:

python install

Furthermore, the test suite can be run by using the following command:

python test


JSON documents and schema must first be loaded into a python dictionary type before it can be validated. This can be done with the JSON parser of your choice but I will use simplejson (just because).

Parsing a simple JSON document

>>> import jsonschema
>>> jsonschema.validate("simplejson", {"type":"string"})

Parsing a more complex JSON document.

>>> import simplejson
>>> import jsonschema
>>> data = simplejson.loads('["foo", {"bar":["baz", null, 1.0, 2]}]')
>>> schema = {
...   "type":"array",
...   "items":[
...     {"type":"string"},
...     {"type":"object",
...      "properties":{
...        "bar":{
...          "items":[
...            {"type":"string"},
...            {"type":"any"},
...            {"type":"number"},
...            {"type":"integer"}
...          ]
...        }
...      }
...    }
...   ]
... }
>>> jsonschema.validate(data,schema)

Handling validation errors ValueErrors are thrown when validation errors occur.

>>> import jsonschema
>>> try:
...     jsonschema.validate("simplejson", {"type":"string","minLength":15})
... except ValueError, e:
...     print e.message
Length of 'simplejson' must be more than 15.000000


jsonschema provides an API similar to simplejson in that validators can be overridden to support special property support or extended functionality. Samples of how jsonschema can be extended can be found in the examples directory.


References are currently not supported. The unique property is currently not validated.