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Ajv logo

Ajv: Another JSON Schema Validator

The fastest JSON Schema validator for Node.js and browser with draft 6 support.

Build Status npm version npm@beta npm downloads Coverage Status Greenkeeper badge Gitter

Please note: Ajv version 6 with JSON Schema draft-07 support is released. Use npm install ajv@beta to install.

Using version 5

JSON Schema draft-06 is published.

Ajv version 5.0.0 that supports draft-06 is released. It may require either migrating your schemas or updating your code (to continue using draft-04 and v5 schemas).

Please note: To use Ajv with draft-04 schemas you need to explicitly add meta-schema to the validator instance:




Ajv generates code using doT templates to turn JSON schemas into super-fast validation functions that are efficient for v8 optimization.

Currently Ajv is the fastest and the most standard compliant validator according to these benchmarks:

Performance of different validators by json-schema-benchmark:



Currently Ajv is the only validator that passes all the tests from JSON Schema Test Suite (according to json-schema-benchmark, apart from the test that requires that 1.0 is not an integer that is impossible to satisfy in JavaScript).


npm install ajv

or to install version 6:

npm install ajv@beta

Getting started

Try it in the Node.js REPL: https://tonicdev.com/npm/ajv

The fastest validation call:

var Ajv = require('ajv');
var ajv = new Ajv(); // options can be passed, e.g. {allErrors: true}
var validate = ajv.compile(schema);
var valid = validate(data);
if (!valid) console.log(validate.errors);

or with less code

// ...
var valid = ajv.validate(schema, data);
if (!valid) console.log(ajv.errors);
// ...


// ...
var valid = ajv.addSchema(schema, 'mySchema')
               .validate('mySchema', data);
if (!valid) console.log(ajv.errorsText());
// ...

See API and Options for more details.

Ajv compiles schemas to functions and caches them in all cases (using schema serialized with fast-json-stable-stringify or a custom function as a key), so that the next time the same schema is used (not necessarily the same object instance) it won’t be compiled again.

The best performance is achieved when using compiled functions returned by compile or getSchema methods (there is no additional function call).

Please note: every time a validation function or ajv.validate are called errors property is overwritten. You need to copy errors array reference to another variable if you want to use it later (e.g., in the callback). See Validation errors

Using in browser

You can require Ajv directly from the code you browserify - in this case Ajv will be a part of your bundle.

If you need to use Ajv in several bundles you can create a separate UMD bundle using npm run bundle script (thanks to siddo420).

Then you need to load Ajv in the browser:

<script src="ajv.min.js"></script>

This bundle can be used with different module systems; it creates global Ajv if no module system is found.

The browser bundle is available on cdnjs.

Ajv is tested with these browsers:

Sauce Test Status

Please note: some frameworks, e.g. Dojo, may redefine global require in such way that is not compatible with CommonJS module format. In such case Ajv bundle has to be loaded before the framework and then you can use global Ajv (see issue #234).

Command line interface

CLI is available as a separate npm package ajv-cli. It supports:

Validation keywords

Ajv supports all validation keywords from draft 4 of JSON-schema standard:

With ajv-keywords package Ajv also supports validation keywords from JSON Schema extension proposals for JSON-schema standard:

See JSON Schema validation keywords for more details.


The following formats are supported for string validation with “format” keyword:

There are two modes of format validation: fast and full. This mode affects formats date, time, date-time, uri, email, and hostname. See Options for details.

You can add additional formats and replace any of the formats above using addFormat method.

The option unknownFormats allows changing the default behaviour when an unknown format is encountered. In this case Ajv can either fail schema compilation (default) or ignore it (default in versions before 5.0.0). You also can whitelist specific format(s) to be ignored. See Options for details.

You can find patterns used for format validation and the sources that were used in formats.js.

Combining schemas with $ref

You can structure your validation logic across multiple schema files and have schemas reference each other using $ref keyword.


var schema = {
  "$id": "http://example.com/schemas/schema.json",
  "type": "object",
  "properties": {
    "foo": { "$ref": "defs.json#/definitions/int" },
    "bar": { "$ref": "defs.json#/definitions/str" }

var defsSchema = {
  "$id": "http://example.com/schemas/defs.json",
  "definitions": {
    "int": { "type": "integer" },
    "str": { "type": "string" }

Now to compile your schema you can either pass all schemas to Ajv instance:

var ajv = new Ajv({schemas: [schema, defsSchema]});
var validate = ajv.getSchema('http://example.com/schemas/schema.json');

or use addSchema method:

var ajv = new Ajv;
var validate = ajv.addSchema(defsSchema)

See Options and addSchema method.

Please note: - $ref is resolved as the uri-reference using schema $id as the base URI (see the example). - References can be recursive (and mutually recursive) to implement the schemas for different data structures (such as linked lists, trees, graphs, etc.). - You don’t have to host your schema files at the URIs that you use as schema $id. These URIs are only used to identify the schemas, and according to JSON Schema specification validators should not expect to be able to download the schemas from these URIs. - The actual location of the schema file in the file system is not used. - You can pass the identifier of the schema as the second parameter of addSchema method or as a property name in schemas option. This identifier can be used instead of (or in addition to) schema $id. - You cannot have the same $id (or the schema identifier) used for more than one schema - the exception will be thrown. - You can implement dynamic resolution of the referenced schemas using compileAsync method. In this way you can store schemas in any system (files, web, database, etc.) and reference them without explicitly adding to Ajv instance. See Asynchronous schema compilation.

$data reference

With $data option you can use values from the validated data as the values for the schema keywords. See proposal for more information about how it works.

$data reference is supported in the keywords: const, enum, format, maximum/minimum, exclusiveMaximum / exclusiveMinimum, maxLength / minLength, maxItems / minItems, maxProperties / minProperties, formatMaximum / formatMinimum, formatExclusiveMaximum / formatExclusiveMinimum, multipleOf, pattern, required, uniqueItems.

The value of “$data” should be a JSON-pointer to the data (the root is always the top level data object, even if the $data reference is inside a referenced subschema) or a relative JSON-pointer (it is relative to the current point in data; if the $data reference is inside a referenced subschema it cannot point to the data outside of the root level for this subschema).


This schema requires that the value in property smaller is less or equal than the value in the property larger:

var ajv = new Ajv({$data: true});

var schema = {
  "properties": {
    "smaller": {
      "type": "number",
      "maximum": { "$data": "1/larger" }
    "larger": { "type": "number" }

var validData = {
  smaller: 5,
  larger: 7

ajv.validate(schema, validData); // true

This schema requires that the properties have the same format as their field names:

var schema = {
  "additionalProperties": {
    "type": "string",
    "format": { "$data": "0#" }

var validData = {
  'date-time': '1963-06-19T08:30:06.283185Z',
  email: 'joe.bloggs@example.com'

$data reference is resolved safely - it won’t throw even if some property is undefined. If $data resolves to undefined the validation succeeds (with the exclusion of const keyword). If $data resolves to incorrect type (e.g. not “number” for maximum keyword) the validation fails.

$merge and $patch keywords

With the package ajv-merge-patch you can use the keywords $merge and $patch that allow extending JSON-schemas with patches using formats JSON Merge Patch (RFC 7396) and JSON Patch (RFC 6902).

To add keywords $merge and $patch to Ajv instance use this code:



Using $merge:

  "$merge": {
    "source": {
      "type": "object",
      "properties": { "p": { "type": "string" } },
      "additionalProperties": false
    "with": {
      "properties": { "q": { "type": "number" } }

Using $patch:

  "$patch": {
    "source": {
      "type": "object",
      "properties": { "p": { "type": "string" } },
      "additionalProperties": false
    "with": [
      { "op": "add", "path": "/properties/q", "value": { "type": "number" } }

The schemas above are equivalent to this schema:

  "type": "object",
  "properties": {
    "p": { "type": "string" },
    "q": { "type": "number" }
  "additionalProperties": false

The properties source and with in the keywords $merge and $patch can use absolute or relative $ref to point to other schemas previously added to the Ajv instance or to the fragments of the current schema.

See the package ajv-merge-patch for more information.

Defining custom keywords

The advantages of using custom keywords are:

If a keyword is used only for side-effects and its validation result is pre-defined, use option valid: true/false in keyword definition to simplify both generated code (no error handling in case of valid: true) and your keyword functions (no need to return any validation result).

The concerns you have to be aware of when extending JSON-schema standard with custom keywords are the portability and understanding of your schemas. You will have to support these custom keywords on other platforms and to properly document these keywords so that everybody can understand them in your schemas.

You can define custom keywords with addKeyword method. Keywords are defined on the ajv instance level - new instances will not have previously defined keywords.

Ajv allows defining keywords with: - validation function - compilation function - macro function - inline compilation function that should return code (as string) that will be inlined in the currently compiled schema.

Example. range and exclusiveRange keywords using compiled schema:

ajv.addKeyword('range', {
  type: 'number',
  compile: function (sch, parentSchema) {
    var min = sch[0];
    var max = sch[1];

    return parentSchema.exclusiveRange === true
            ? function (data) { return data > min && data < max; }
            : function (data) { return data >= min && data <= max; }

var schema = { "range": [2, 4], "exclusiveRange": true };
var validate = ajv.compile(schema);
console.log(validate(2.01)); // true
console.log(validate(3.99)); // true
console.log(validate(2)); // false
console.log(validate(4)); // false

Several custom keywords (typeof, instanceof, range and propertyNames) are defined in ajv-keywords package - they can be used for your schemas and as a starting point for your own custom keywords.

See Defining custom keywords for more details.

Asynchronous schema compilation

During asynchronous compilation remote references are loaded using supplied function. See compileAsync method and loadSchema option.


var ajv = new Ajv({ loadSchema: loadSchema });

ajv.compileAsync(schema).then(function (validate) {
  var valid = validate(data);
  // ...

function loadSchema(uri) {
  return request.json(uri).then(function (res) {
    if (res.statusCode >= 400)
      throw new Error('Loading error: ' + res.statusCode);
    return res.body;

Please note: Option missingRefs should NOT be set to "ignore" or "fail" for asynchronous compilation to work.

Asynchronous validation

Example in Node.js REPL: https://tonicdev.com/esp/ajv-asynchronous-validation

You can define custom formats and keywords that perform validation asynchronously by accessing database or some other service. You should add async: true in the keyword or format definition (see addFormat, addKeyword and Defining custom keywords).

If your schema uses asynchronous formats/keywords or refers to some schema that contains them it should have "$async": true keyword so that Ajv can compile it correctly. If asynchronous format/keyword or reference to asynchronous schema is used in the schema without $async keyword Ajv will throw an exception during schema compilation.

Please note: all asynchronous subschemas that are referenced from the current or other schemas should have "$async": true keyword as well, otherwise the schema compilation will fail.

Validation function for an asynchronous custom format/keyword should return a promise that resolves with true or false (or rejects with new Ajv.ValidationError(errors) if you want to return custom errors from the keyword function). Ajv compiles asynchronous schemas to either es7 async functions that can optionally be transpiled with nodent or with regenerator or to generator functions that can be optionally transpiled with regenerator as well. You can also supply any other transpiler as a function. See Options.

The compiled validation function has $async: true property (if the schema is asynchronous), so you can differentiate these functions if you are using both synchronous and asynchronous schemas.

If you are using generators, the compiled validation function can be either wrapped with co (default) or returned as generator function, that can be used directly, e.g. in koa 1.0. co is a small library, it is included in Ajv (both as npm dependency and in the browser bundle).

Async functions are currently supported in Chrome 55, Firefox 52, Node.js 7 (with –harmony-async-await) and MS Edge 13 (with flag).

Generator functions are currently supported in Chrome, Firefox and Node.js.

If you are using Ajv in other browsers or in older versions of Node.js you should use one of available transpiling options. All provided async modes use global Promise class. If your platform does not have Promise you should use a polyfill that defines it.

Validation result will be a promise that resolves with validated data or rejects with an exception Ajv.ValidationError that contains the array of validation errors in errors property.


 * Default mode is non-transpiled generator function wrapped with `co`.
 * Using package ajv-async (https://github.com/epoberezkin/ajv-async)
 * you can auto-detect the best async mode.
 * In this case, without "async" and "transpile" options
 * (or with option {async: true})
 * Ajv will choose the first supported/installed option in this order:
 * 1. native async function
 * 2. native generator function wrapped with co
 * 3. es7 async functions transpiled with nodent
 * 4. es7 async functions transpiled with regenerator

var setupAsync = require('ajv-async');
var ajv = setupAsync(new Ajv);

ajv.addKeyword('idExists', {
  async: true,
  type: 'number',
  validate: checkIdExists

function checkIdExists(schema, data) {
  return knex(schema.table)
  .where('id', data)
  .then(function (rows) {
    return !!rows.length; // true if record is found

var schema = {
  "$async": true,
  "properties": {
    "userId": {
      "type": "integer",
      "idExists": { "table": "users" }
    "postId": {
      "type": "integer",
      "idExists": { "table": "posts" }

var validate = ajv.compile(schema);

validate({ userId: 1, postId: 19 })
.then(function (data) {
  console.log('Data is valid', data); // { userId: 1, postId: 19 }
.catch(function (err) {
  if (!(err instanceof Ajv.ValidationError)) throw err;
  // data is invalid
  console.log('Validation errors:', err.errors);

Using transpilers with asynchronous validation functions.

To use a transpiler you should separately install it (or load its bundle in the browser).

Ajv npm package includes minified browser bundles of regenerator and nodent in dist folder.

Using nodent

var setupAsync = require('ajv-async');
var ajv = new Ajv({ /* async: 'es7', */ transpile: 'nodent' });
var validate = ajv.compile(schema); // transpiled es7 async function

npm install nodent or use nodent.min.js from dist folder of npm package.

Using regenerator

var setupAsync = require('ajv-async');
var ajv = new Ajv({ /* async: 'es7', */ transpile: 'regenerator' });
var validate = ajv.compile(schema); // transpiled es7 async function

npm install regenerator or use regenerator.min.js from dist folder of npm package.

Using other transpilers

var ajv = new Ajv({ async: 'es7', processCode: transpileFunc });
var validate = ajv.compile(schema); // transpiled es7 async function

See Options.

Comparison of async modes

mode transpile
es7 async
- 0.75 -
- 1.0 -
es7.nodent 1.35 1.1 215Kb
es7.regenerator 1.0 2.7 1109Kb
regenerator 1.0 3.2 1109Kb

* Relative performance in Node.js 7.x — smaller is better.

nodent has several advantages:

Filtering data

With option removeAdditional (added by andyscott) you can filter data during the validation.

This option modifies original data.


var ajv = new Ajv({ removeAdditional: true });
var schema = {
  "additionalProperties": false,
  "properties": {
    "foo": { "type": "number" },
    "bar": {
      "additionalProperties": { "type": "number" },
      "properties": {
        "baz": { "type": "string" }

var data = {
  "foo": 0,
  "additional1": 1, // will be removed; `additionalProperties` == false
  "bar": {
    "baz": "abc",
    "additional2": 2 // will NOT be removed; `additionalProperties` != false

var validate = ajv.compile(schema);

console.log(validate(data)); // true
console.log(data); // { "foo": 0, "bar": { "baz": "abc", "additional2": 2 }

If removeAdditional option in the example above were "all" then both additional1 and additional2 properties would have been removed.

If the option were "failing" then property additional1 would have been removed regardless of its value and property additional2 would have been removed only if its value were failing the schema in the inner additionalProperties (so in the example above it would have stayed because it passes the schema, but any non-number would have been removed).

Please note: If you use removeAdditional option with additionalProperties keyword inside anyOf/oneOf keywords your validation can fail with this schema, for example:

  "type": "object",
  "oneOf": [
      "properties": {
        "foo": { "type": "string" }
      "required": [ "foo" ],
      "additionalProperties": false
      "properties": {
        "bar": { "type": "integer" }
      "required": [ "bar" ],
      "additionalProperties": false

The intention of the schema above is to allow objects with either the string property “foo” or the integer property “bar”, but not with both and not with any other properties.

With the option removeAdditional: true the validation will pass for the object { "foo": "abc"} but will fail for the object {"bar": 1}. It happens because while the first subschema in oneOf is validated, the property bar is removed because it is an additional property according to the standard (because it is not included in properties keyword in the same schema).

While this behaviour is unexpected (issues #129, #134), it is correct. To have the expected behaviour (both objects are allowed and additional properties are removed) the schema has to be refactored in this way:

  "type": "object",
  "properties": {
    "foo": { "type": "string" },
    "bar": { "type": "integer" }
  "additionalProperties": false,
  "oneOf": [
    { "required": [ "foo" ] },
    { "required": [ "bar" ] }

The schema above is also more efficient - it will compile into a faster function.

Assigning defaults

With option useDefaults Ajv will assign values from default keyword in the schemas of properties and items (when it is the array of schemas) to the missing properties and items.

This option modifies original data.

Please note: by default the default value is inserted in the generated validation code as a literal (starting from v4.0), so the value inserted in the data will be the deep clone of the default in the schema.

If you need to insert the default value in the data by reference pass the option useDefaults: "shared".

Inserting defaults by reference can be faster (in case you have an object in default) and it allows to have dynamic values in defaults, e.g. timestamp, without recompiling the schema. The side effect is that modifying the default value in any validated data instance will change the default in the schema and in other validated data instances. See example 3 below.

Example 1 (default in properties):

var ajv = new Ajv({ useDefaults: true });
var schema = {
  "type": "object",
  "properties": {
    "foo": { "type": "number" },
    "bar": { "type": "string", "default": "baz" }
  "required": [ "foo", "bar" ]

var data = { "foo": 1 };

var validate = ajv.compile(schema);

console.log(validate(data)); // true
console.log(data); // { "foo": 1, "bar": "baz" }

Example 2 (default in items):

var schema = {
  "type": "array",
  "items": [
    { "type": "number" },
    { "type": "string", "default": "foo" }

var data = [ 1 ];

var validate = ajv.compile(schema);

console.log(validate(data)); // true
console.log(data); // [ 1, "foo" ]

Example 3 (inserting “defaults” by reference):

var ajv = new Ajv({ useDefaults: 'shared' });

var schema = {
  properties: {
    foo: {
      default: { bar: 1 }

var validate = ajv.compile(schema);

var data = {};
console.log(validate(data)); // true
console.log(data); // { foo: { bar: 1 } }

data.foo.bar = 2;

var data2 = {};
console.log(validate(data2)); // true
console.log(data2); // { foo: { bar: 2 } }

default keywords in other cases are ignored:

Coercing data types

When you are validating user inputs all your data properties are usually strings. The option coerceTypes allows you to have your data types coerced to the types specified in your schema type keywords, both to pass the validation and to use the correctly typed data afterwards.

This option modifies original data.

Please note: if you pass a scalar value to the validating function its type will be coerced and it will pass the validation, but the value of the variable you pass won’t be updated because scalars are passed by value.

Example 1:

var ajv = new Ajv({ coerceTypes: true });
var schema = {
  "type": "object",
  "properties": {
    "foo": { "type": "number" },
    "bar": { "type": "boolean" }
  "required": [ "foo", "bar" ]

var data = { "foo": "1", "bar": "false" };

var validate = ajv.compile(schema);

console.log(validate(data)); // true
console.log(data); // { "foo": 1, "bar": false }

Example 2 (array coercions):

var ajv = new Ajv({ coerceTypes: 'array' });
var schema = {
  "properties": {
    "foo": { "type": "array", "items": { "type": "number" } },
    "bar": { "type": "boolean" }

var data = { "foo": "1", "bar": ["false"] };

var validate = ajv.compile(schema);

console.log(validate(data)); // true
console.log(data); // { "foo": [1], "bar": false }

The coercion rules, as you can see from the example, are different from JavaScript both to validate user input as expected and to have the coercion reversible (to correctly validate cases where different types are defined in subschemas of “anyOf” and other compound keywords).

See Coercion rules for details.


new Ajv(Object options) -> Object

Create Ajv instance.

.compile(Object schema) -> Function<Object data>

Generate validating function and cache the compiled schema for future use.

Validating function returns boolean and has properties errors with the errors from the last validation (null if there were no errors) and schema with the reference to the original schema.

Unless the option validateSchema is false, the schema will be validated against meta-schema and if schema is invalid the error will be thrown. See options.

.compileAsync(Object schema [, Boolean meta] [, Function callback]) -> Promise

Asynchronous version of compile method that loads missing remote schemas using asynchronous function in options.loadSchema. This function returns a Promise that resolves to a validation function. An optional callback passed to compileAsync will be called with 2 parameters: error (or null) and validating function. The returned promise will reject (and the callback will be called with an error) when:

The function compiles schema and loads the first missing schema (or meta-schema) until all missing schemas are loaded.

You can asynchronously compile meta-schema by passing true as the second parameter.

See example in Asynchronous compilation.

.validate(Object schema|String key|String ref, data) -> Boolean

Validate data using passed schema (it will be compiled and cached).

Instead of the schema you can use the key that was previously passed to addSchema, the schema id if it was present in the schema or any previously resolved reference.

Validation errors will be available in the errors property of Ajv instance (null if there were no errors).

Please note: every time this method is called the errors are overwritten so you need to copy them to another variable if you want to use them later.

If the schema is asynchronous (has $async keyword on the top level) this method returns a Promise. See Asynchronous validation.

.addSchema(Array<Object>|Object schema [, String key]) -> Ajv

Add schema(s) to validator instance. This method does not compile schemas (but it still validates them). Because of that dependencies can be added in any order and circular dependencies are supported. It also prevents unnecessary compilation of schemas that are containers for other schemas but not used as a whole.

Array of schemas can be passed (schemas should have ids), the second parameter will be ignored.

Key can be passed that can be used to reference the schema and will be used as the schema id if there is no id inside the schema. If the key is not passed, the schema id will be used as the key.

Once the schema is added, it (and all the references inside it) can be referenced in other schemas and used to validate data.

Although addSchema does not compile schemas, explicit compilation is not required - the schema will be compiled when it is used first time.

By default the schema is validated against meta-schema before it is added, and if the schema does not pass validation the exception is thrown. This behaviour is controlled by validateSchema option.

Please note: Ajv uses the method chaining syntax for all methods with the prefix add* and remove*. This allows you to do nice things like the following.

var validate = new Ajv().addSchema(schema).addFormat(name, regex).getSchema(uri);
.addMetaSchema(Array<Object>|Object schema [, String key]) -> Ajv

Adds meta schema(s) that can be used to validate other schemas. That function should be used instead of addSchema because there may be instance options that would compile a meta schema incorrectly (at the moment it is removeAdditional option).

There is no need to explicitly add draft 6 meta schema (http://json-schema.org/draft-06/schema and http://json-schema.org/schema) - it is added by default, unless option meta is set to false. You only need to use it if you have a changed meta-schema that you want to use to validate your schemas. See validateSchema.

.validateSchema(Object schema) -> Boolean

Validates schema. This method should be used to validate schemas rather than validate due to the inconsistency of uri format in JSON Schema standard.

By default this method is called automatically when the schema is added, so you rarely need to use it directly.

If schema doesn’t have $schema property, it is validated against draft 6 meta-schema (option meta should not be false).

If schema has $schema property, then the schema with this id (that should be previously added) is used to validate passed schema.

Errors will be available at ajv.errors.

.getSchema(String key) -> Function<Object data>

Retrieve compiled schema previously added with addSchema by the key passed to addSchema or by its full reference (id). The returned validating function has schema property with the reference to the original schema.

.removeSchema([Object schema|String key|String ref|RegExp pattern]) -> Ajv

Remove added/cached schema. Even if schema is referenced by other schemas it can be safely removed as dependent schemas have local references.

Schema can be removed using: - key passed to addSchema - it’s full reference (id) - RegExp that should match schema id or key (meta-schemas won’t be removed) - actual schema object that will be stable-stringified to remove schema from cache

If no parameter is passed all schemas but meta-schemas will be removed and the cache will be cleared.

.addFormat(String name, String|RegExp|Function|Object format) -> Ajv

Add custom format to validate strings or numbers. It can also be used to replace pre-defined formats for Ajv instance.

Strings are converted to RegExp.

Function should return validation result as true or false.

If object is passed it should have properties validate, compare and async:

Custom formats can be also added via formats option.

.addKeyword(String keyword, Object definition) -> Ajv

Add custom validation keyword to Ajv instance.

Keyword should be different from all standard JSON schema keywords and different from previously defined keywords. There is no way to redefine keywords or to remove keyword definition from the instance.

Keyword must start with a letter, _ or $, and may continue with letters, numbers, _, $, or -. It is recommended to use an application-specific prefix for keywords to avoid current and future name collisions.

Example Keywords: - "xyz-example": valid, and uses prefix for the xyz project to avoid name collisions. - "example": valid, but not recommended as it could collide with future versions of JSON schema etc. - "3-example": invalid as numbers are not allowed to be the first character in a keyword

Keyword definition is an object with the following properties:

compile, macro and inline are mutually exclusive, only one should be used at a time. validate can be used separately or in addition to them to support $data reference.

Please note: If the keyword is validating data type that is different from the type(s) in its definition, the validation function will not be called (and expanded macro will not be used), so there is no need to check for data type inside validation function or inside schema returned by macro function (unless you want to enforce a specific type and for some reason do not want to use a separate type keyword for that). In the same way as standard keywords work, if the keyword does not apply to the data type being validated, the validation of this keyword will succeed.

See Defining custom keywords for more details.

.getKeyword(String keyword) -> Object|Boolean

Returns custom keyword definition, true for pre-defined keywords and false if the keyword is unknown.

.removeKeyword(String keyword) -> Ajv

Removes custom or pre-defined keyword so you can redefine them.

While this method can be used to extend pre-defined keywords, it can also be used to completely change their meaning - it may lead to unexpected results.

Please note: schemas compiled before the keyword is removed will continue to work without changes. To recompile schemas use removeSchema method and compile them again.

.errorsText([Array<Object> errors [, Object options]]) -> String

Returns the text with all errors in a String.

Options can have properties separator (string used to separate errors, “,” by default) and dataVar (the variable name that dataPaths are prefixed with, “data” by default).



  // validation and reporting options:
  $data:            false,
  allErrors:        false,
  verbose:          false,
  jsonPointers:     false,
  uniqueItems:      true,
  unicode:          true,
  format:           'fast',
  formats:          {},
  unknownFormats:   true,
  schemas:          {},
  logger:           undefined,
  // referenced schema options:
  schemaId:         undefined // recommended '$id'
  missingRefs:      true,
  extendRefs:       'ignore', // recommended 'fail'
  loadSchema:       undefined, // function(uri: string): Promise {}
  // options to modify validated data:
  removeAdditional: false,
  useDefaults:      false,
  coerceTypes:      false,
  // asynchronous validation options:
  async:            'co*',
  transpile:        undefined, // requires ajv-async package
  // advanced options:
  meta:             true,
  validateSchema:   true,
  addUsedSchema:    true,
  inlineRefs:       true,
  passContext:      false,
  loopRequired:     Infinity,
  ownProperties:    false,
  multipleOfPrecision: false,
  errorDataPath:    'object',
  messages:         true,
  sourceCode:       false,
  processCode:      undefined, // function (str: string): string {}
  cache:            new Cache,
  serialize:        undefined
Validation and reporting options
Referenced schema options
Options to modify validated data
Asynchronous validation options
Advanced options

Validation errors

In case of validation failure, Ajv assigns the array of errors to errors property of validation function (or to errors property of Ajv instance when validate or validateSchema methods were called). In case of asynchronous validation, the returned promise is rejected with exception Ajv.ValidationError that has errors property.

Error objects

Each error is an object with the following properties:

Please note: propertyNames keyword schema validation errors have an additional property propertyName, dataPath points to the object. After schema validation for each property name, if it is invalid an additional error is added with the property keyword equal to "propertyNames".

Error parameters

Properties of params object in errors depend on the keyword that failed validation.

Some packages using Ajv


npm install
git submodule update --init
npm test


All validation functions are generated using doT templates in dot folder. Templates are precompiled so doT is not a run-time dependency.

npm run build - compiles templates to dotjs folder.

npm run watch - automatically compiles templates when files in dot folder change

Please see Contributing guidelines

Changes history

See https://github.com/epoberezkin/ajv/releases

Please note: Changes in version 5.0.0.

Changes in version 4.6.0.

Changes in version 4.0.0.

Changes in version 3.0.0.

Changes in version 2.0.0.