JSON Schema Compiled checK
CoffeeScript JavaScript
Latest commit 28307cd Oct 5, 2015 @gilesbowkett gilesbowkett cleanup


JSON Schema Compiled checK

JSCK is one of the fastest JSON Schema validators for Node.js. It supports JSON Schema drafts 3 and 4, with a few caveats (see the Coverage section below).

Installation and Usage

Install with NPM:

npm install --save jsck


JSCK = require "jsck"

JSCK can create validators from multiple schemas, but this requires that each schema be identified with a URI in a top-level "id" field. In many cases, only a single schema is needed, and there is no need to uniquely identify the schema. This is the easiest way to use JSCK, as it is a common pattern.

# Construct a validator for a schema lacking an "id" declaration

jsck = new JSCK.draft4
  type: "object"
      type: "object"
      required: ["login"]
          type: "string"
          pattern: "^[\\w\\d_]{3,32}$"
          type: "string"
          format: "email"

console.log "valid document:", jsck.validate
    login: "matthew"
    email: "matthew@pandastrike.com"

{errors} = jsck.validate
    login: "matthew"
    email: "pandastrike.com"

console.log "invalid document:", errors

To use Draft 3 schemas:

validator = new JSCK.draft3(schema)

See these advanced usage examples for help working with multiple schemas.


JSCK is faster than most other JavaScript/CoffeeScript libraries for validating JSON Schemas because it "compiles" the schemas. That is, JSCK generates the tree of functions needed to validate a particular schema when you construct a validator. The schema is thus traversed only during preparation, and most of the work of interpreting the schema is done at this time, rather than for every document submitted for validation. This minimizes the work required during validation, which leads to substantial performance improvements over non-compiling validators.


Draft 4

JSCK passes all tests in the canonical JSON Schema Test Suite, except for these items:

  • use of maxLength and minLength with Unicode surrogate pairs.
  • refRemote (this is an essential feature we do plan to support)
  • ref
    • remote ref, containing refs itself
  • uniqueItems
  • optional/zeroTerminatedFloats

Draft 3

Currently passing the canonical test suite for draft3 except for these items:

  • refRemote
  • ref
    • remote ref, containing refs itself
  • uniqueItems
  • optional/zeroTerminatedFloats

Managing resolution scope with the "id" attribute

JSCK does not support the full range of scope manipulations suggested by JSON Schema drafts 3 and 4. Scope manipulation is a controversial topic, and with JSCK we have chosen to play it safe, supporting "id" declarations only in cases that will (probably) not lead to any ambiguity. Specifically, JSCK uses "id" declarations only in these cases:

  • at the top level of a schema, to provide a namespace for schemas not loaded from URIs.
  • non-JSON-pointer fragments ("id": "#user"), which serve merely as aliases for specific subschemas, and are thus convenient and unambiguous.

For more information on the topic of the "id" attribute and scope manipulation, see this issue: https://github.com/json-schema/json-schema/issues/77.


To contribute, hack on it, or run the tests:

git clone git@github.com:pandastrike/jsck.git
cd jsck
coffee tasks/update
npm install


JSCK uses the official JSON Schema Test Suite as well as some custom tests. To run all tests for all versions:

coffee test

See this document for more information on working with JSCK tests.


JSCK has fairly comprehensive benchmarks which show it to be one of the very fastest JSON Schema validators available for Node.js. Pull requests welcome, of course.

Because performance varies (at very least) based on the complexity of the schema being validated, we run benchmarks against several different schemas, ranging from quite simple to moderately complex.

For JSON Schema Draft4, we run benchmarks against JSCK, tv4, jayschema, z-schema, and other validators. On the trivial schema, our benchmarks produce this relative performance for these validators (lower is better):

ajv : 1
jsen : 2.9
is-my-json-valid : 4.4
Themis (minimal) : 5.2
Themis : 5.3
JSCK : 34.2
z-schema : 48.3
tv4 : 54.4
jayschema : 2507.4

For the schema of medium complexity, our benchmarks produce this relative performance for the tested validators (lower is better):

ajv : 1
is-my-json-valid : 2.8
jsen : 3.0
Themis (minimal) : 11.1
Themis : 11.6
JSCK : 22.0
tv4 : 43.4
z-schema : 46.0
jayschema : 2319.4

For the schema of higher complexity, our benchmarks produce this relative performance for the tested validators (lower is better):

ajv : 1
is-my-json-valid : 1.23
jsen : 1.31
Themis (minimal) : 1.7
Themis : 1.8
JSCK : 4.8
z-schema : 17.2
tv4 : 27.0
jayschema : 1215.1

As the complexity of the schema increases, the performance benefits of the compilation model become more evident.

See this document for detailed results and information on running and creating benchmarks.