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    2.20.6 • Public • Published


    A JSONSchema validator that uses code generation to be extremely fast.

    It passes the entire JSONSchema v4 test suite except for remoteRefs and maxLength/minLength when using unicode surrogate pairs.

    build status


    npm install --save is-my-json-valid


    Simply pass a schema to compile it

    var validator = require('is-my-json-valid')
    var validate = validator({
      required: true,
      type: 'object',
      properties: {
        hello: {
          required: true,
          type: 'string'
    console.log('should be valid', validate({hello: 'world'}))
    console.log('should not be valid', validate({}))
    // get the last list of errors by checking validate.errors
    // the following will print [{field: 'data.hello', message: 'is required'}]

    You can also pass the schema as a string

    var validate = validator('{"type": ... }')

    Optionally you can use the require submodule to load a schema from __dirname

    var validator = require('is-my-json-valid/require')
    var validate = validator('my-schema.json')

    Custom formats

    is-my-json-valid supports the formats specified in JSON schema v4 (such as date-time). If you want to add your own custom formats pass them as the formats options to the validator

    var validate = validator({
      type: 'string',
      required: true,
      format: 'only-a'
    }, {
      formats: {
        'only-a': /^a+$/
    console.log(validate('aa')) // true
    console.log(validate('ab')) // false

    External schemas

    You can pass in external schemas that you reference using the $ref attribute as the schemas option

    var ext = {
      required: true,
      type: 'string'
    var schema = {
      $ref: '#ext' // references another schema called ext
    // pass the external schemas as an option
    var validate = validator(schema, {schemas: {ext: ext}})
    validate('hello') // returns true
    validate(42) // return false

    Filtering away additional properties

    is-my-json-valid supports filtering away properties not in the schema

    var filter = validator.filter({
      required: true,
      type: 'object',
      properties: {
        hello: {type: 'string', required: true}
      additionalProperties: false
    var doc = {hello: 'world', notInSchema: true}
    console.log(filter(doc)) // {hello: 'world'}

    Verbose mode shows more information about the source of the error

    When the verbose options is set to true, is-my-json-valid also outputs:

    • value: The data value that caused the error
    • schemaPath: an array of keys indicating which sub-schema failed
    var schema = {
      required: true,
      type: 'object',
      properties: {
        hello: {
          required: true,
          type: 'string'
    var validate = validator(schema, {
      verbose: true
    validate({hello: 100});
    // [ { field: 'data.hello',
    //     message: 'is the wrong type',
    //     value: 100,
    //     type: 'string',
    //     schemaPath: [ 'properties', 'hello' ] } ]

    Many popular libraries make it easy to retrieve the failing rule with the schemaPath:

    var schemaPath = validate.errors[0].schemaPath
    var R = require('ramda')
    console.log( 'All evaluate to the same thing: ', R.equals(,
      { required: true, type: 'string' },
      R.path(schemaPath, schema),
      require('lodash').get(schema, schemaPath),
      require('jsonpointer').get(schema, [""].concat(schemaPath))
    // All evaluate to the same thing: true

    Greedy mode tries to validate as much as possible

    By default is-my-json-valid bails on first validation error but when greedy is set to true it tries to validate as much as possible:

    var validate = validator({
      type: 'object',
      properties: {
        x: {
          type: 'number'
      required: ['x', 'y']
    }, {
      greedy: true
    validate({x: 'string'});
    console.log(validate.errors) // [{field: 'data.y', message: 'is required'},
                                 //  {field: 'data.x', message: 'is the wrong type'}]

    Error messages

    Here is a list of possible message values for errors:

    • is required
    • is the wrong type
    • has additional items
    • must be FORMAT format (FORMAT is the format property from the schema)
    • must be unique
    • must be an enum value
    • dependencies not set
    • has additional properties
    • referenced schema does not match
    • negative schema matches
    • pattern mismatch
    • no schemas match
    • no (or more than one) schemas match
    • has a remainder
    • has more properties than allowed
    • has less properties than allowed
    • has more items than allowed
    • has less items than allowed
    • has longer length than allowed
    • has less length than allowed
    • is less than minimum
    • is more than maximum


    is-my-json-valid uses code generation to turn your JSON schema into basic javascript code that is easily optimizeable by v8.

    At the time of writing, is-my-json-valid is the fastest validator when running

    If you know any other relevant benchmarks open a PR and I'll add them.

    TypeScript support

    This library ships with TypeScript typings. They are still early on and not perfect at the moment, but should hopefully handle the most common cases. If you find anything that doesn't work, please open an issue and we'll try to solve it.

    The typings are using unknown and thus require TypeScript 3.0 or later.

    Here is a quick sample of usage together with express:

    import createError = require('http-errors')
    import createValidator = require('is-my-json-valid')
    import { Request, Response, NextFunction } from 'express'
    const personValidator = createValidator({
      type: 'object',
      properties: {
        name: { type: 'string' },
        age: { type: 'number' },
      required: [
    export function post (req: Request, res: Response, next: NextFunction) {
      // Here req.body is typed as: any
      if (!personValidator(req.body)) {
        throw createError(400, { errors: personValidator.errors })
      // Here req.body is typed as: { name: string, age: number | undefined }

    As you can see, the typings for is-my-json-valid will contruct an interface from the schema passed in. This allows you to work with your incoming json body in a type safe way.




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