# Ajv options

# Usage

This page describes properties of the options object that can be passed to Ajv constructor.

For example, to report all validation errors (rather than failing on the first errors) you should pass allErrors option to constructor:

const ajv = new Ajv({allErrors: true})

# Option defaults

Do NOT pass default options

Passing the value below for some of the options is equivalent to not passing this option at all. There is no need to pass default option values - it is recommended to only pass option values that are different from defaults.

// see types/index.ts for actual types
const defaultOptions = {
  // strict mode options (NEW)
  strict: undefined, // *
  strictSchema: true, // *
  strictNumbers: true, // *
  strictTypes: "log", // *
  strictTuples: "log", // *
  strictRequired: false, // *
  allowUnionTypes: false, // *
  allowMatchingProperties: false, // *
  validateFormats: true, // *
  // validation and reporting options:
  $data: false, // *
  allErrors: false,
  verbose: false,
  discriminator: false, // *
  unicodeRegExp: true, // *
  timestamp: undefined // **
  parseDate: false // **
  allowDate: false // **
  int32range: true // **
  $comment: false, // *
  formats: {},
  keywords: {},
  schemas: {},
  logger: undefined,
  loadSchema: undefined, // *, function(uri: string): Promise {}
  // options to modify validated data:
  removeAdditional: false,
  useDefaults: false, // *
  coerceTypes: false, // *
  // advanced options:
  meta: true,
  validateSchema: true,
  addUsedSchema: true,
  inlineRefs: true,
  passContext: false,
  loopRequired: 200, // *
  loopEnum: 200, // NEW
  ownProperties: false,
  multipleOfPrecision: undefined, // *
  messages: true, // false with JTD
  uriResolver: undefined,
  code: {
    // NEW
    es5: false,
    esm: false,
    lines: false,
    source: false,
    process: undefined, // (code: string) => string
    optimize: true,
    regExp: RegExp

* only with JSON Schema

** only with JSON Type Definition

# Strict mode options v7

# strict

By default Ajv executes in strict mode, that is designed to prevent any unexpected behaviours or silently ignored mistakes in schemas (see Strict Mode for more details). It does not change any validation results, but it makes some schemas invalid that would be otherwise valid according to JSON Schema specification.

Option values:

  • true - throw an exception when any strict mode restriction is violated.
  • "log" - log warning when any strict mode restriction is violated.
  • false - ignore all strict mode violations.
  • undefined (default) - use defaults for options strictSchema, strictNumbers, strictTypes, strictTuples and strictRequired.

# strictSchema

Prevent unknown keywords, formats etc. (see Strict schema)

Option values:

  • true (default) - throw an exception when any strict schema restriction is violated.
  • "log" - log warning when any strict schema restriction is violated.
  • false - ignore all strict schema violations.

# strictNumbers

Whether to accept NaN and Infinity as number types during validation.

Option values:

  • true (default) - fail validation if NaN or Infinity is passed where number is expected.
  • false - allow NaN and Infinity as number.

# strictTypes

See Strict types

Option values:

  • true - throw an exception when any strict types restriction is violated.
  • "log" (default) - log warning when any strict types restriction is violated.
  • false - ignore all strict types violations.

# strictTuples

See Unconstrained tuples

Option values:

  • true - throw an exception when any strict tuples restriction is violated.
  • "log" (default) - log warning when any strict tuples restriction is violated.
  • false - ignore all strict tuples violations.

# strictRequired

See Defined required properties

Option values:

  • true - throw an exception when strict required restriction is violated.
  • "log" - log warning when strict required restriction is violated.
  • false (default) - ignore strict required violations.

# allowUnionTypes

Pass true to allow using multiple non-null types in "type" keyword (one of strictTypes restrictions). see Strict types

# allowMatchingProperties

Pass true to allow overlap between "properties" and "patternProperties". Does not affect other strict mode restrictions. See Strict Mode.

# validateFormats

Format validation.

Option values:

  • true (default) - validate formats (see Formats). In strict mode unknown formats will throw exception during schema compilation (and fail validation in case format keyword value is $data reference).
  • false - do not validate any format keywords (TODO they will still collect annotations once supported).

# Validation and reporting options

# $data

Support $data references. Draft 6 meta-schema that is added by default will be extended to allow them. If you want to use another meta-schema you need to use $dataMetaSchema method to add support for $data reference. See API.

# allErrors

Check all rules collecting all errors. Default is to return after the first error.

# verbose

Include the reference to the part of the schema (schema and parentSchema) and validated data in errors (false by default).

# discriminator

Support discriminator keyword from OpenAPI specification (opens new window).

# unicodeRegExp

By default Ajv uses unicode flag "u" with "pattern" and "patternProperties", as per JSON Schema spec. See RegExp.prototype.unicode (opens new window) .

Option values:

  • true (default) - use unicode flag "u".
  • false - do not use flag "u".

# timestamp JTD only

Defines which Javascript types will be accepted for the JTD timestamp type.

By default Ajv will accept both Date objects and RFC3339 (opens new window) strings. You can specify allowed values with the option timestamp: "date" or timestamp: "string".

# parseDate JTD only

Defines how date-time strings are parsed by JTD parsers. By default Ajv parses date-time strings as string. Use parseDate: true to parse them as Date objects.

# allowDate JTD only

Defines how date-time strings are parsed and validated. By default Ajv only allows full date-time strings, as required by JTD specification. Use allowDate: true to allow date strings both for validation and for parsing.

Option allowDate is not portable

This option makes JTD validation and parsing more permissive and non-standard. The date strings without time part will be accepted by Ajv, but will be rejected by other JTD validators.

# int32range JTD only

Can be used to disable range checking for int32 and uint32 types.

By default Ajv limits the range of these types to [-2**31, 2**31 - 1] for int32 and to [0, 2**32-1] for uint32 when validating and parsing.

With option int32range: false Ajv only requires that uint32 is non-negative, otherwise does not check the range. Parser will limit the number size to 16 digits (approx. 2**53 - safe integer range).

Option int32range is not portable

This option makes JTD validation and parsing more permissive and non-standard. The integers within a wider range will be accepted by Ajv, but will be rejected by other JTD validators.

# $comment

Log or pass the value of $comment keyword to a function.

Option values:

  • false (default): ignore $comment keyword.
  • true: log the keyword value to console.
  • function: pass the keyword value, its schema path and root schema to the specified function

# formats

An object with format definitions. Keys and values will be passed to addFormat method. Pass true as format definition to ignore some formats.

# keywords

An array of keyword definitions or strings. Values will be passed to addKeyword method.

# schemas

An array or object of schemas that will be added to the instance. In case you pass the array the schemas must have IDs in them. When the object is passed the method addSchema(value, key) will be called for each schema in this object.

# logger

Sets the logging method. Default is the global console object that should have methods log, warn and error. See Error logging.

Option values:

  • logger instance - it should have methods log, warn and error. If any of these methods is missing an exception will be thrown.
  • false - logging is disabled.

# loadSchema

Asynchronous function that will be used to load remote schemas when compileAsync method is used and some reference is missing (option missingRefs should NOT be 'fail' or 'ignore'). This function should accept remote schema uri as a parameter and return a Promise that resolves to a schema. See example in Asynchronous compilation.

# Options to modify validated data

# removeAdditional

Remove additional properties - see example in Removing additional properties.

This option is not used if schema is added with addMetaSchema method.

Option values:

  • false (default) - not to remove additional properties
  • "all" - all additional properties are removed, regardless of additionalProperties keyword in schema (and no validation is made for them).
  • true - only additional properties with additionalProperties keyword equal to false are removed.
  • "failing" - additional properties that fail schema validation will be removed (where additionalProperties keyword is false or schema).

# useDefaults

Replace missing or undefined properties and items with the values from corresponding default keywords. Default behaviour is to ignore default keywords. This option is not used if schema is added with addMetaSchema method.

See examples in Assigning defaults.

Option values:

  • false (default) - do not use defaults
  • true - insert defaults by value (object literal is used).
  • "empty" - in addition to missing or undefined, use defaults for properties and items that are equal to null or "" (an empty string).

# coerceTypes

Change data type of data to match type keyword. See the example in Coercing data types and coercion rules.

Option values:

  • false (default) - no type coercion.
  • true - coerce scalar data types.
  • "array" - in addition to coercions between scalar types, coerce scalar data to an array with one element and vice versa (as required by the schema).

# Advanced options

# meta

Add meta-schema (opens new window) so it can be used by other schemas (true by default). If an object is passed, it will be used as the default meta-schema for schemas that have no $schema keyword. This default meta-schema MUST have $schema keyword.

# validateSchema

Validate added/compiled schemas against meta-schema (true by default). $schema property in the schema can be http://json-schema.org/draft-07/schema or absent (draft-07 meta-schema will be used) or can be a reference to the schema previously added with addMetaSchema method.

Option values:

  • true (default) - if the validation fails, throw the exception.
  • "log" - if the validation fails, log error.
  • false - skip schema validation.

# addUsedSchema

By default methods compile and validate add schemas to the instance if they have $id (or id) property that doesn't start with "#". If $id is present and it is not unique the exception will be thrown. Set this option to false to skip adding schemas to the instance and the $id uniqueness check when these methods are used. This option does not affect addSchema method.

# inlineRefs

Affects compilation of referenced schemas.

Option values:

  • true (default) - the referenced schemas that don't have refs in them are inlined, regardless of their size - it improves performance.
  • false - to not inline referenced schemas (they will always be compiled as separate functions).
  • integer number - to limit the maximum number of keywords of the schema that will be inlined (to balance the total size of compiled functions and performance).

# passContext

Pass validation context to compile and validate keyword functions. If this option is true and you pass some context to the compiled validation function with validate.call(context, data), the context will be available as this in your keywords. By default this is Ajv instance.

# loopRequired

By default required keyword is compiled into a single expression (or a sequence of statements in allErrors mode) up to 200 required properties. Pass integer to set a different number of properties above which required keyword will be validated in a loop (with a smaller validation function size and worse performance).

# loopEnum v7

By default enum keyword is compiled into a single expression with up to 200 allowed values. Pass integer to set the number of values above which enum keyword will be validated in a loop (with a smaller validation function size and worse performance).

# ownProperties

By default Ajv iterates over all enumerable object properties; when this option is true only own enumerable object properties (i.e. found directly on the object rather than on its prototype) are iterated. Contributed by @mbroadst.

# multipleOfPrecision

By default multipleOf keyword is validated by comparing the result of division with parseInt() of that result. It works for dividers that are bigger than 1. For small dividers such as 0.01 the result of the division is usually not integer (even when it should be integer, see issue #84 (opens new window)). If you need to use fractional dividers set this option to some positive integer N to have multipleOf validated using this formula: Math.abs(Math.round(division) - division) < 1e-N (it is slower but allows for float arithmetic deviations).

# messages

Include human-readable messages in errors. true by default. false can be passed when messages are generated outside of Ajv code (e.g. with ajv-i18n (opens new window)).

# uriResolver

By default uriResolver is undefined and relies on the embedded uriResolver fast-uri (opens new window). Pass an object that satisfies the interface UriResolver (opens new window) to be used in replacement. One alternative is uri-js (opens new window).

# code v7

Code generation options:

type CodeOptions = {
  es5?: boolean // to generate es5 code - by default code is es6, with "for-of" loops, "let" and "const"
  esm?: boolean // how functions should be exported - by default CJS is used, so the validate function(s) 
  // file can be `required`. Set this value to true to export the validate function(s) as ES Modules, enabling 
  // bunlers to do their job.
  lines?: boolean // add line-breaks to code - to simplify debugging of generated functions
  source?: boolean // add `source` property (see Source below) to validating function.
  process?: (code: string, schema?: SchemaEnv) => string // an optional function to process generated code
  // before it is passed to Function constructor.
  // It can be used to either beautify or to transpile code.
  optimize?: boolean | number // code optimization flag or number of passes, 1 pass by default,
  // code optimizations reduce the size of the generated code (bytes, based on the tests) by over 10%,
  // the number of code tree nodes by nearly 17%.
  // You would almost never need more than one optimization pass, unless you have some really complex schemas -
  // the second pass in the tests (it has quite complex schemas) only improves optimization by less than 0.1%.
  // See [Code optimization](./codegen.md#code-optimization) for details.
  formats?: Code
  // Code snippet created with `_` tagged template literal that contains all format definitions,
  // it can be the code of actual definitions or `require` call:
  // _`require("./my-formats")`
  regExp: RegExpEngine
  // Pass non-standard RegExp engine to mitigate ReDoS, e.g. node-re2.
  // During validation of a schema, code.regExp will be 
  // used to match strings against regular expressions.
  // The supplied function must support the interface:
  // regExp(regex, unicodeFlag).test(string) => boolean

type Source = {
  code: string // unlike func.toString() it includes assignments external to function scope
  scope: Scope // see Code generation (TODO)