Code Quality Rank: L2
Monthly Downloads: 0
Programming language: JavaScript
License: MIT License
Tags: JSON     Data Validation     Schema     Jsonschema     Orderly    
Latest version: v2.20.0

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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.



*Note that all licence references and agreements mentioned in the is-my-json-valid README section above are relevant to that project's source code only.