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A public domain JSON Schema validator for JavaScript

Tiny Validator (for v4 JSON Schema)

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Use json-schema draft v4 to validate simple values and complex objects using a rich validation vocabulary (examples).

There is support for $ref with JSON Pointer fragment paths (other-schema.json#/properties/myKey).

Usage 1: Simple validation

var valid = tv4.validate(data, schema);

If validation returns false, then an explanation of why validation failed can be found in tv4.error.

The error object will look something like:

    "code": 0,
    "message": "Invalid type: string",
    "dataPath": "/intKey",
    "schemaPath": "/properties/intKey/type"

The "code" property will refer to one of the values in tv4.errorCodes - in this case, tv4.errorCodes.INVALID_TYPE.

To enable external schema to be referenced, you use:

tv4.addSchema(url, schema);

If schemas are referenced ($ref) but not known, then validation will return true and the missing schema(s) will be listed in tv4.missing. For more info see the API documentation below.

Usage 2: Multi-threaded validation

Storing the error and missing schemas does not work well in multi-threaded environments, so there is an alternative syntax:

var result = tv4.validateResult(data, schema);

The result will look something like:

    "valid": false,
    "error": {...},
    "missing": [...]

Usage 3: Multiple errors

Normally, tv4 stops when it encounters the first validation error. However, you can collect an array of validation errors using:

var result = tv4.validateMultiple(data, schema);

The result will look something like:

    "valid": false,
    "errors": [
    "missing": [...]

Asynchronous validation

Support for asynchronous validation (where missing schemas are fetched) can be added by including an extra JavaScript file. Currently, the only version requires jQuery (tv4.async-jquery.js), but the code is very short and should be fairly easy to modify for other libraries (such as MooTools).


tv4.validate(data, schema, function (isValid, validationError) { ... });

validationFailure is simply taken from tv4.error.

Cyclical JavaScript objects

While they don't occur in proper JSON, JavaScript does support self-referencing objects. Any of the above calls support an optional third argument: checkRecursive. If true, tv4 will handle self-referencing objects properly - this slows down validation slightly, but that's better than a hanging script.

Consider this data, notice how both a and b refer to each other:

var a = {};
var b = { a: a };
a.b = b;
var aSchema = { properties: { b: { $ref: 'bSchema' }}};
var bSchema = { properties: { a: { $ref: 'aSchema' }}};
tv4.addSchema('aSchema', aSchema);
tv4.addSchema('bSchema', bSchema);

If the checkRecursive argument were missing, this would throw a "too much recursion" error.

To enable support for this, pass true as additional argument to any of the regular validation methods:

tv4.validate(a, aSchema, true);
tv4.validateResult(data, aSchema, true);
tv4.validateMultiple(data, aSchema, true);

The banUnknownProperties flag

Sometimes, it is desirable to flag all unknown properties as an error. This is especially useful during development, to catch typos and the like, even when extra custom-defined properties are allowed.

As such, tv4 implements "ban unknown properties" mode, enabled by a fourth-argument flag:

tv4.validate(data, schema, checkRecursive, true);
tv4.validateResult(data, schema, checkRecursive, true);
tv4.validateMultiple(data, schema, checkRecursive, true);


There are additional api commands available for more complex use-cases:

addSchema(uri, schema)

Pre-register a schema for reference by other schema and synchronous validation.

tv4.addSchema('', { ... });
  • uri the uri to identify this schema.
  • schema the schema object.

Schemas that have their id property set can be added directly.

tv4.addSchema({ ... });

Return a schema from the cache.

  • uri the uri of the schema (may contain a # fragment)
var schema = tv4.getSchema('');

Return a shallow copy of the schema cache, mapping schema document URIs to schema objects.

var map = tv4.getSchemaMap();
var schema = map[uri];

Return an Array with known schema document URIs.

  • filter optional RegExp to filter URIs
var arr = tv4.getSchemaUris();
// optional filter using a RegExp
var arr = tv4.getSchemaUris(/^https?://;

Return an Array with schema document URIs that are used as $ref in known schemas but which currently have no associated schema data.

Use this in combination with tv4.addSchema(uri, schema) to preload the cache for complete synchronous validation with.

  • filter optional RegExp to filter URIs
var arr = tv4.getMissingUris();
// optional filter using a RegExp
var arr = tv4.getMissingUris(/^https?://;

Drop all known schema document URIs from the cache.


Return a new tv4 instance with no shared state.

var otherTV4 = tv4.freshApi();

Manually reset validation status from the simple tv4.validate(data, schema). Although tv4 will self reset on each validation there are some implementation scenarios where this is useful.


Sets a custom error reporter. This is a function that accepts three arguments, and returns an error message (string):

tv4.setErrorReporter(function (error, data, schema) {
    return "Error code: " + error.code;

The error object already has everything aside from the .message property filled in (so you can use error.params, error.dataPath, error.schemaPath etc.).

If nothing is returned (or the empty string), then it falls back to the default error reporter. To remove a custom error reporter, call tv4.setErrorReporter(null).


Sets the language used by the default error reporter.

  • code is a language code, like 'en' or 'en-gb'

If you specify a multi-level language code (e.g. fr-CH), then it will fall back to the generic version (fr) if needed.

addLanguage(code, map)

Add a new template-based language map for the default error reporter (used by tv4.language(code))

  • code is new language code
  • map is an object mapping error IDs or constant names (e.g. 103 or "NUMBER_MAXIMUM") to language strings.
tv4.addLanguage('fr', { ... });
// select for use

If you register a multi-level language code (e.g. fr-FR), then it will also be registered for plain fr if that does not already exist.

addFormat(format, validationFunction)

Add a custom format validator. (There are no built-in format validators. Several common ones can be found here though)

  • format is a string, corresponding to the "format" value in schemas.
  • validationFunction is a function that either returns:
    • null (meaning no error)
    • an error string (explaining the reason for failure)
tv4.addFormat('decimal-digits', function (data, schema) {
    if (typeof data === 'string' && !/^[0-9]+$/.test(data)) {
        return null;
    return "must be string of decimal digits";

Alternatively, multiple formats can be added at the same time using an object:

    'my-format': function () {...},
    'other-format': function () {...}
defineKeyword(keyword, validationFunction)

Add a custom keyword validator.

  • keyword is a string, corresponding to a schema keyword
  • validationFunction is a function that either returns:
    • null (meaning no error)
    • an error string (explaining the reason for failure)
    • an error object (containing some of: code/message/dataPath/schemaPath)
tv4.defineKeyword('my-custom-keyword', function (data, value, schema) {
    if (simpleFailure()) {
        return "Failure";
    } else if (detailedFailure()) {
        return {code: tv4.errorCodes.MY_CUSTOM_CODE, message: {param1: 'a', param2: 'b'}};
    } else {
        return null;

schema is the schema upon which the keyword is defined. In the above example, value === schema['my-custom-keyword'].

If an object is returned from the custom validator, and its message is a string, then that is used as the message result. If message is an object, then that is used to populate the (localisable) error template.

defineError(codeName, codeNumber, defaultMessage)

Defines a custom error code.

  • codeName is a string, all-caps underscore separated, e.g. "MY_CUSTOM_ERROR"
  • codeNumber is an integer > 10000, which will be stored in tv4.errorCodes (e.g. tv4.errorCodes.MY_CUSTOM_ERROR)
  • defaultMessage is an error message template to use (assuming translations have not been provided for this code)

An example of defaultMessage might be: "Incorrect moon (expected {expected}, got {actual}"). This is filled out if a custom keyword returns a object message (see above). Translations will be used, if associated with the correct code name/number.


Basic usage

var schema = {
	"items": {
		"type": "boolean"
var data1 = [true, false];
var data2 = [true, 123];

alert("data 1: " + tv4.validate(data1, schema)); // true alert("data 2: " + tv4.validate(data2, schema)); // false alert("data 2 error: " + JSON.stringify(tv4.error, null, 4));

Use of $ref

var schema = {
	"type": "array",
	"items": {"$ref": "#"}
var data1 = [[], [[]]];
var data2 = [[], [true, []]];

alert("data 1: " + tv4.validate(data1, schema)); // true alert("data 2: " + tv4.validate(data2, schema)); // false

Missing schema

var schema = {
	"type": "array",
	"items": {"$ref": "" }
var data = [1, 2, 3];

alert("Valid: " + tv4.validate(data, schema)); // true alert("Missing schemas: " + JSON.stringify(tv4.missing));

Referencing remote schema

tv4.addSchema("", {
	"definitions": {
		"arrayItem": {"type": "boolean"}
var schema = {
	"type": "array",
	"items": {"$ref": "" }
var data1 = [true, false, true];
var data2 = [1, 2, 3];

alert("data 1: " + tv4.validate(data1, schema)); // true alert("data 2: " + tv4.validate(data2, schema)); // false

Supported platforms

  • Node.js
  • All modern browsers
  • IE >= 7


You can manually download tv4.js or the minified tv4.min.js and include it in your html to create the global tv4 variable.

Alternately use it as a CommonJS module:

var tv4 = require('tv4');

or as an AMD module (e.g. with requirejs):

require('tv4', function(tv4){
  //use tv4 here 

There is a command-line tool that wraps this library: tv4-cmd.


$ npm install tv4


$ bower install tv4

$ component install geraintluff/tv4

Build and test

You can rebuild and run the node and browser tests using node.js and grunt:

Make sure you have the global grunt cli command:

$ npm install grunt-cli -g

Clone the git repos, open a shell in the root folder and install the development dependencies:

$ npm install

Rebuild and run the tests:

$ grunt

It will run a build and display one Spec-style report for the node.js and two Dot-style reports for both the plain and minified browser tests (via phantomJS). You can also use your own browser to manually run the suites by opening test/index.html and test/index-min.html.


Pull-requests for fixes and expansions are welcome. Edit the partial files in /source and add your tests in a suitable suite or folder under /test/tests and run grunt to rebuild and run the test suite. Try to maintain an idiomatic coding style and add tests for any new features. It is recommend to discuss big changes in an Issue.

Do you speak another language? tv4 needs internationalisation - please contribute language files to /lang!

Packages using tv4


The code is available as "public domain", meaning that it is completely free to use, without any restrictions at all. Read the full license here.

It's also available under an MIT license.