This is an implementation of the [JSON Schema specification](http://www.json-schema.org) written in pure Java. This allows pure server side JSON schema validation if this is what you are looking for.

The draft serving as a reference is, at the moment, draft version 3, which can be found [here](http://json-schema.org/draft-03/schema) (version 4 is around the corner, for some defintion of "corner" -- understand, days, or a few weeks). This implementation has full support for instance validation using draft v3, and can be extended to support draft v4 easily.

Version 0.3 is out: see [here] (https://github.com/fge/json-schema-validator/wiki/ChangeLog) for a list of features. Among others, it performs more than 25 times better than the previous version.

Small overview of available features:

• ability to register/unregister keywords;
• validator/schema caching;
• arbitrary length/precision number validation;
• full report or fail-fast report modes;
• complete $ref support, with loop detection;
• ECMA 262 regexes (using Rhino);
• ability to register URI handlers for any scheme (HTTP only natively);
• others.

I believe this to be the most complete implementation of JSON Schema in Java today.

For a detailed discussion of the implementation, see [here](https://github.com/fge/json-schema-validator/wiki/Status). For a list of planned features for next versions, see [here](https://github.com/fge/json-schema-validator/wiki/Roadmap).

Please see the wiki for more details.