A Haskell implementation of the most commonly used JSON Schema specification (Draft 4).

Notes

As of 2017 json-schema-org has begun releasing new drafts of the standard. Once this work stabilizes hjsonschema will add coverage for the latest draft.
Requires pcre (pkgs.pcre in Nixpkgs).
Schemas with circular references can cause infinite loops. hjsonschema does loop detection but it may not be solid yet -- please open an issue if you find a situation where it fails.

Example

See here.

Run all tests:

stack test

Run only local tests:

stack test hjsonschema:local

Run remote tests (makes GETs to json-schema.org, also temporarily starts an HTTP server on port 1234):

stack test hjsonschema:remote

Be a correct and fast implementation of the spec.
Be a useful reference for implementers in other languages. Haskell's high level nature, expressive type system and referential transparency suit this purpose well.

Passes all the required tests in the language agnostic test suite.
Very modular, which should make it easy to support future versions of the specification.

Uses the pcre-heavy regular expression library for the "pattern" validator. It should use a library based on the ECMA 262 regex dialect, which the spec requires.
Currently doesn't support the optional "format" validators.

JSON-Schema-Test-Suite is vendored from commit # aabcb3427745ade7a0b4d49ff016ad7eda8b898b here.
src/draft4.json is from commit # f3d5aeb5ffbe9d9a5a0ceb761dc47c7c4c2efa68 here.

TJ Weigel created the logo.

Tim Baumann wrote aeson-schema, on which hjsonschema's test code and its implementation of SchemaGraph were based.