README.md

##### <a name="api-compileAsync"></a>.compileAsync(Object schema [, Boolean meta] [, Function callback]) -&gt; 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:

- missing schema can't be loaded (`loadSchema` returns a Promise that rejects).
- a schema containing a missing reference is loaded, but the reference cannot be resolved.
- schema (or some loaded/referenced schema) is invalid.

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](#asynchronous-schema-compilation).


##### .validate(Object schema|String key|String ref, data) -&gt; 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](#asynchronous-validation).


##### .addSchema(Array&lt;Object&gt;|Object schema [, String key]) -&gt; 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](https://en.wikipedia.org/wiki/Method_chaining) for all methods with the prefix `add*` and `remove*`.
This allows you to do nice things like the following.

```javascript
var validate = new Ajv().addSchema(schema).addFormat(name, regex).getSchema(uri);
```

##### .addMetaSchema(Array&lt;Object&gt;|Object schema [, String key]) -&gt; 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-07 meta schema (http://json-schema.org/draft-07/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`.


##### <a name="api-validateschema"></a>.validateSchema(Object schema) -&gt; 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) -&gt; Function&lt;Object data&gt;

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]) -&gt; 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.


##### <a name="api-addformat"></a>.addFormat(String name, String|RegExp|Function|Object format) -&gt; 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`:

- _validate_: a string, RegExp or a function as described above.
- _compare_: an optional comparison function that accepts two strings and compares them according to the format meaning. This function is used with keywords `formatMaximum`/`formatMinimum` (defined in [ajv-keywords](https://github.com/ajv-validator/ajv-keywords) package). It should return `1` if the first value is bigger than the second value, `-1` if it is smaller and `0` if it is equal.
- _async_: an optional `true` value if `validate` is an asynchronous function; in this case it should return a promise that resolves with a value `true` or `false`.
- _type_: an optional type of data that the format applies to. It can be `"string"` (default) or `"number"` (see https://github.com/ajv-validator/ajv/issues/291#issuecomment-259923858). If the type of data is different, the validation will pass.

Custom formats can be also added via `formats` option.


##### <a name="api-addkeyword"></a>.addKeyword(String keyword, Object definition) -&gt; 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:

- _type_: optional string or array of strings with data type(s) that the keyword applies to. If not present, the keyword will apply to all types.
- _validate_: validating function
- _compile_: compiling function
- _macro_: macro function
- _inline_: compiling function that returns code (as string)
- _schema_: an optional `false` value used with "validate" keyword to not pass schema
- _metaSchema_: an optional meta-schema for keyword schema
- _dependencies_: an optional list of properties that must be present in the parent schema - it will be checked during schema compilation
- _modifying_: `true` MUST be passed if keyword modifies data
- _statements_: `true` can be passed in case inline keyword generates statements (as opposed to expression)
- _valid_: pass `true`/`false` to pre-define validation result, the result returned from validation function will be ignored. This option cannot be used with macro keywords.
- _$data_: an optional `true` value to support [$data reference](#data-reference) as the value of custom keyword. The reference will be resolved at validation time. If the keyword has meta-schema it would be extended to allow $data and it will be used to validate the resolved value. Supporting $data reference requires that keyword has validating function (as the only option or in addition to compile, macro or inline function).
- _async_: an optional `true` value if the validation function is asynchronous (whether it is compiled or passed in _validate_ property); in this case it should return a promise that resolves with a value `true` or `false`. This option is ignored in case of "macro" and "inline" keywords.
- _errors_: an optional boolean or string `"full"` indicating whether keyword returns errors. If this property is not set Ajv will determine if the errors were set in case of failed validation.

_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](#defining-custom-keywords) for more details.


##### .getKeyword(String keyword) -&gt; Object|Boolean

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


##### .removeKeyword(String keyword) -&gt; 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&lt;Object&gt; errors [, Object options]]) -&gt; 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).


## Options

Defaults:

```javascript
{
  // validation and reporting options:
  $data:            false,
  allErrors:        false,
  verbose:          false,
  $comment:         false, // NEW in Ajv version 6.0
  jsonPointers:     false,
  uniqueItems:      true,
  unicode:          true,
  nullable:         false,
  format:           'fast',
  formats:          {},
  unknownFormats:   true,
  schemas:          {},
  logger:           undefined,
  // referenced schema options:
  schemaId:         '$id',
  missingRefs:      true,
  extendRefs:       'ignore', // recommended 'fail'
  loadSchema:       undefined, // function(uri: string): Promise {}
  // options to modify validated data:
  removeAdditional: false,
  useDefaults:      false,
  coerceTypes:      false,
  // strict mode options
  strictDefaults:   false,
  strictKeywords:   false,
  strictNumbers:    false,
  // asynchronous validation options:
  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', // deprecated
  messages:         true,
  sourceCode:       false,
  processCode:      undefined, // function (str: string, schema: object): string {}
  cache:            new Cache,
  serialize:        undefined
}
```

##### Validation and reporting options

- _$data_: support [$data references](#data-reference). 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 $data reference. See [API](#api).
- _allErrors_: check all rules collecting all errors. Default is to return after the first error.
- _verbose_: include the reference to the part of the schema (`schema` and `parentSchema`) and validated data in errors (false by default).
- _$comment_ (NEW in Ajv version 6.0): log or pass the value of `$comment` keyword to a function. Option values:
  - `false` (default): ignore $comment keyword.
  - `true`: log the keyword value to console.
  - function: pass the keyword value, its schema path and root schema to the specified function
- _jsonPointers_: set `dataPath` property of errors using [JSON Pointers](https://tools.ietf.org/html/rfc6901) instead of JavaScript property access notation.
- _uniqueItems_: validate `uniqueItems` keyword (true by default).
- _unicode_: calculate correct length of strings with unicode pairs (true by default). Pass `false` to use `.length` of strings that is faster, but gives "incorrect" lengths of strings with unicode pairs - each unicode pair is counted as two characters.
- _nullable_: support keyword "nullable" from [Open API 3 specification](https://swagger.io/docs/specification/data-models/data-types/).
- _format_: formats validation mode. Option values:
  - `"fast"` (default) - simplified and fast validation (see [Formats](#formats) for details of which formats are available and affected by this option).
  - `"full"` - more restrictive and slow validation. E.g., 25:00:00 and 2015/14/33 will be invalid time and date in 'full' mode but it will be valid in 'fast' mode.
  - `false` - ignore all format keywords.
- _formats_: an object with custom formats. Keys and values will be passed to `addFormat` method.
- _keywords_: an object with custom keywords. Keys and values will be passed to `addKeyword` method.
- _unknownFormats_: handling of unknown formats. Option values:
  - `true` (default) - if an unknown format is encountered the exception is thrown during schema compilation. If `format` keyword value is [$data reference](#data-reference) and it is unknown the validation will fail.
  - `[String]` - an array of unknown format names that will be ignored. This option can be used to allow usage of third party schemas with format(s) for which you don't have definitions, but still fail if another unknown format is used. If `format` keyword value is [$data reference](#data-reference) and it is not in this array the validation will fail.
  - `"ignore"` - to log warning during schema compilation and always pass validation (the default behaviour in versions before 5.0.0). This option is not recommended, as it allows to mistype format name and it won't be validated without any error message. This behaviour is required by JSON Schema specification.
- _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](#error-logging). Option values:
  - custom logger - it should have methods `log`, `warn` and `error`. If any of these methods is missing an exception will be thrown.
  - `false` - logging is disabled.


##### Referenced schema options

- _schemaId_: this option defines which keywords are used as schema URI. Option value:
  - `"$id"` (default) - only use `$id` keyword as schema URI (as specified in JSON Schema draft-06/07), ignore `id` keyword (if it is present a warning will be logged).
  - `"id"` - only use `id` keyword as schema URI (as specified in JSON Schema draft-04), ignore `$id` keyword (if it is present a warning will be logged).
  - `"auto"` - use both `$id` and `id` keywords as schema URI. If both are present (in the same schema object) and different the exception will be thrown during schema compilation.
- _missingRefs_: handling of missing referenced schemas. Option values:
  - `true` (default) - if the reference cannot be resolved during compilation the exception is thrown. The thrown error has properties `missingRef` (with hash fragment) and `missingSchema` (without it). Both properties are resolved relative to the current base id (usually schema id, unless it was substituted).
  - `"ignore"` - to log error during compilation and always pass validation.
  - `"fail"` - to log error and successfully compile schema but fail validation if this rule is checked.
- _extendRefs_: validation of other keywords when `$ref` is present in the schema. Option values:
  - `"ignore"` (default) - when `$ref` is used other keywords are ignored (as per [JSON Reference](https://tools.ietf.org/html/draft-pbryan-zyp-json-ref-03#section-3) standard). A warning will be logged during the schema compilation.
  - `"fail"` (recommended) - if other validation keywords are used together with `$ref` the exception will be thrown when the schema is compiled. This option is recommended to make sure schema has no keywords that are ignored, which can be confusing.
  - `true` - validate all keywords in the schemas with `$ref` (the default behaviour in versions before 5.0.0).
- _loadSchema_: asynchronous function that will be used to load remote schemas when `compileAsync` [method](#api-compileAsync) 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](#asynchronous-schema-compilation).


##### Options to modify validated data

- _removeAdditional_: remove additional properties - see example in [Filtering data](#filtering-data). 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](#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).
  - `"shared"` (deprecated) - insert defaults by reference. If the default is an object, it will be shared by all instances of validated data. If you modify the inserted default in the validated data, it will be modified in the schema as well.
- _coerceTypes_: change data type of data to match `type` keyword. See the example in [Coercing data types](#coercing-data-types) and [coercion rules](https://github.com/ajv-validator/ajv/blob/master/COERCION.md). 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).


##### Strict mode options

- _strictDefaults_: report ignored `default` keywords in schemas. Option values:
  - `false` (default) - ignored defaults are not reported
  - `true` - if an ignored default is present, throw an error
  - `"log"` - if an ignored default is present, log warning
- _strictKeywords_: report unknown keywords in schemas. Option values:
  - `false` (default) - unknown keywords are not reported
  - `true` - if an unknown keyword is present, throw an error
  - `"log"` - if an unknown keyword is present, log warning
- _strictNumbers_: validate numbers strictly, failing validation for NaN and Infinity. Option values:
  - `false` (default) - NaN or Infinity will pass validation for numeric types
  - `true` - NaN or Infinity will not pass validation for numeric types

##### Asynchronous validation options

- _transpile_: Requires [ajv-async](https://github.com/ajv-validator/ajv-async) package. It determines whether Ajv transpiles compiled asynchronous validation function. Option values:
  - `undefined` (default) - transpile with [nodent](https://github.com/MatAtBread/nodent) if async functions are not supported.
  - `true` - always transpile with nodent.
  - `false` - do not transpile; if async functions are not supported an exception will be thrown.


##### Advanced options

- _meta_: add [meta-schema](http://json-schema.org/documentation.html) 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 - that substantially improves performance at the cost of the bigger size of compiled schema functions.
  - `false` - to not inline referenced schemas (they will be compiled as separate functions).
  - integer number - to limit the maximum number of keywords of the schema that will be inlined.
- _passContext_: pass validation context to custom 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 custom 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). In case of a very large number of properties in this keyword it may result in a very big validation function. Pass integer to set the number of properties above which `required` keyword will be validated in a loop - smaller validation function size but also 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](https://github.com/ajv-validator/ajv/issues/84)). 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 arithmetics deviations).
- _errorDataPath_ (deprecated): set `dataPath` to point to 'object' (default) or to 'property' when validating keywords `required`, `additionalProperties` and `dependencies`.
- _messages_: Include human-readable messages in errors. `true` by default. `false` can be passed when custom messages are used (e.g. with [ajv-i18n](https://github.com/ajv-validator/ajv-i18n)).
- _sourceCode_: add `sourceCode` property to validating function (for debugging; this code can be different from the result of toString call).
- _processCode_: an optional function to process generated code before it is passed to Function constructor. It can be used to either beautify (the validating function is generated without line-breaks) or to transpile code. Starting from version 5.0.0 this option replaced options:
  - `beautify` that formatted the generated function using [js-beautify](https://github.com/beautify-web/js-beautify). If you want to beautify the generated code pass a function calling `require('js-beautify').js_beautify` as `processCode: code => js_beautify(code)`.
  - `transpile` that transpiled asynchronous validation function. You can still use `transpile` option with [ajv-async](https://github.com/ajv-validator/ajv-async) package. See [Asynchronous validation](#asynchronous-validation) for more information.
- _cache_: an optional instance of cache to store compiled schemas using stable-stringified schema as a key. For example, set-associative cache [sacjs](https://github.com/epoberezkin/sacjs) can be used. If not passed then a simple hash is used which is good enough for the common use case (a limited number of statically defined schemas). Cache should have methods `put(key, value)`, `get(key)`, `del(key)` and `clear()`.
- _serialize_: an optional function to serialize schema to cache key. Pass `false` to use schema itself as a key (e.g., if WeakMap used as a cache). By default [fast-json-stable-stringify](https://github.com/epoberezkin/fast-json-stable-stringify) is used.


## 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](#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:

- _keyword_: validation keyword.
- _dataPath_: the path to the part of the data that was validated. By default `dataPath` uses JavaScript property access notation (e.g., `".prop[1].subProp"`). When the option `jsonPointers` is true (see [Options](#options)) `dataPath` will be set using JSON pointer standard (e.g., `"/prop/1/subProp"`).
- _schemaPath_: the path (JSON-pointer as a URI fragment) to the schema of the keyword that failed validation.
- _params_: the object with the additional information about error that can be used to create custom error messages (e.g., using [ajv-i18n](https://github.com/ajv-validator/ajv-i18n) package). See below for parameters set by all keywords.
- _message_: the standard error message (can be excluded with option `messages` set to false).
- _schema_: the schema of the keyword (added with `verbose` option).
- _parentSchema_: the schema containing the keyword (added with `verbose` option)
- _data_: the data validated by the keyword (added with `verbose` option).

__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.

- `maxItems`, `minItems`, `maxLength`, `minLength`, `maxProperties`, `minProperties` - property `limit` (number, the schema of the keyword).
- `additionalItems` - property `limit` (the maximum number of allowed items in case when `items` keyword is an array of schemas and `additionalItems` is false).
- `additionalProperties` - property `additionalProperty` (the property not used in `properties` and `patternProperties` keywords).
- `dependencies` - properties:
  - `property` (dependent property),
  - `missingProperty` (required missing dependency - only the first one is reported currently)
  - `deps` (required dependencies, comma separated list as a string),
  - `depsCount` (the number of required dependencies).
- `format` - property `format` (the schema of the keyword).
- `maximum`, `minimum` - properties:
  - `limit` (number, the schema of the keyword),
  - `exclusive` (boolean, the schema of `exclusiveMaximum` or `exclusiveMinimum`),
  - `comparison` (string, comparison operation to compare the data to the limit, with the data on the left and the limit on the right; can be "<", "<=", ">", ">=")
- `multipleOf` - property `multipleOf` (the schema of the keyword)
- `pattern` - property `pattern` (the schema of the keyword)
- `required` - property `missingProperty` (required property that is missing).
- `propertyNames` - property `propertyName` (an invalid property name).
- `patternRequired` (in ajv-keywords) - property `missingPattern` (required pattern that did not match any property).
- `type` - property `type` (required type(s), a string, can be a comma-separated list)
- `uniqueItems` - properties `i` and `j` (indices of duplicate items).
- `const` - property `allowedValue` pointing to the value (the schema of the keyword).
- `enum` - property `allowedValues` pointing to the array of values (the schema of the keyword).
- `$ref` - property `ref` with the referenced schema URI.
- `oneOf` - property `passingSchemas` (array of indices of passing schemas, null if no schema passes).
- custom keywords (in case keyword definition doesn't create errors) - property `keyword` (the keyword name).


### Error logging

Using the `logger` option when initiallizing Ajv will allow you to define custom logging. Here you can build upon the exisiting logging. The use of other logging packages is supported as long as the package or its associated wrapper exposes the required methods. If any of the required methods are missing an exception will be thrown.
- **Required Methods**: `log`, `warn`, `error`

```javascript
var otherLogger = new OtherLogger();
var ajv = new Ajv({
  logger: {
    log: console.log.bind(console),
    warn: function warn() {
      otherLogger.logWarn.apply(otherLogger, arguments);
    },
    error: function error() {
      otherLogger.logError.apply(otherLogger, arguments);
      console.error.apply(console, arguments);
    }
  }
});
```


## Plugins

Ajv can be extended with plugins that add custom keywords, formats or functions to process generated code. When such plugin is published as npm package it is recommended that it follows these conventions:

- it exports a function
- this function accepts ajv instance as the first parameter and returns the same instance to allow chaining
- this function can accept an optional configuration as the second parameter

If you have published a useful plugin please submit a PR to add it to the next section.


## Related packages

- [ajv-async](https://github.com/ajv-validator/ajv-async) - plugin to configure async validation mode
- [ajv-bsontype](https://github.com/BoLaMN/ajv-bsontype) - plugin to validate mongodb's bsonType formats
- [ajv-cli](https://github.com/jessedc/ajv-cli) - command line interface
- [ajv-errors](https://github.com/ajv-validator/ajv-errors) - plugin for custom error messages
- [ajv-i18n](https://github.com/ajv-validator/ajv-i18n) - internationalised error messages
- [ajv-istanbul](https://github.com/ajv-validator/ajv-istanbul) - plugin to instrument generated validation code to measure test coverage of your schemas
- [ajv-keywords](https://github.com/ajv-validator/ajv-keywords) - plugin with custom validation keywords (select, typeof, etc.)
- [ajv-merge-patch](https://github.com/ajv-validator/ajv-merge-patch) - plugin with keywords $merge and $patch
- [ajv-pack](https://github.com/ajv-validator/ajv-pack) - produces a compact module exporting validation functions
- [ajv-formats-draft2019](https://github.com/luzlab/ajv-formats-draft2019) - format validators for draft2019 that aren't already included in ajv (ie. `idn-hostname`, `idn-email`, `iri`, `iri-reference` and `duration`).

## Some packages using Ajv

- [webpack](https://github.com/webpack/webpack) - a module bundler. Its main purpose is to bundle JavaScript files for usage in a browser
- [jsonscript-js](https://github.com/JSONScript/jsonscript-js) - the interpreter for [JSONScript](http://www.jsonscript.org) - scripted processing of existing endpoints and services
- [osprey-method-handler](https://github.com/mulesoft-labs/osprey-method-handler) - Express middleware for validating requests and responses based on a RAML method object, used in [osprey](https://github.com/mulesoft/osprey) - validating API proxy generated from a RAML definition
- [har-validator](https://github.com/ahmadnassri/har-validator) - HTTP Archive (HAR) validator
- [jsoneditor](https://github.com/josdejong/jsoneditor) - a web-based tool to view, edit, format, and validate JSON http://jsoneditoronline.org
- [JSON Schema Lint](https://github.com/nickcmaynard/jsonschemalint) - a web tool to validate JSON/YAML document against a single JSON Schema http://jsonschemalint.com
- [objection](https://github.com/vincit/objection.js) - SQL-friendly ORM for Node.js
- [table](https://github.com/gajus/table) - formats data into a string table
- [ripple-lib](https://github.com/ripple/ripple-lib) - a JavaScript API for interacting with [Ripple](https://ripple.com) in Node.js and the browser
- [restbase](https://github.com/wikimedia/restbase) - distributed storage with REST API & dispatcher for backend services built to provide a low-latency & high-throughput API for Wikipedia / Wikimedia content
- [hippie-swagger](https://github.com/CacheControl/hippie-swagger) - [Hippie](https://github.com/vesln/hippie) wrapper that provides end to end API testing with swagger validation
- [react-form-controlled](https://github.com/seeden/react-form-controlled) - React controlled form components with validation
- [rabbitmq-schema](https://github.com/tjmehta/rabbitmq-schema) - a schema definition module for RabbitMQ graphs and messages
- [@query/schema](https://www.npmjs.com/package/@query/schema) - stream filtering with a URI-safe query syntax parsing to JSON Schema
- [chai-ajv-json-schema](https://github.com/peon374/chai-ajv-json-schema) - chai plugin to us JSON Schema with expect in mocha tests
- [grunt-jsonschema-ajv](https://github.com/SignpostMarv/grunt-jsonschema-ajv) - Grunt plugin for validating files against JSON Schema
- [extract-text-webpack-plugin](https://github.com/webpack-contrib/extract-text-webpack-plugin) - extract text from bundle into a file
- [electron-builder](https://github.com/electron-userland/electron-builder) - a solution to package and build a ready for distribution Electron app
- [addons-linter](https://github.com/mozilla/addons-linter) - Mozilla Add-ons Linter
- [gh-pages-generator](https://github.com/epoberezkin/gh-pages-generator) - multi-page site generator converting markdown files to GitHub pages
- [ESLint](https://github.com/eslint/eslint) - the pluggable linting utility for JavaScript and JSX


## Tests

```
npm install
git submodule update --init
npm test
```

## Contributing

All validation functions are generated using doT templates in [dot](https://github.com/ajv-validator/ajv/tree/master/lib/dot) folder. Templates are precompiled so doT is not a run-time dependency.

`npm run build` - compiles templates to [dotjs](https://github.com/ajv-validator/ajv/tree/master/lib/dotjs) folder.

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

Please see [Contributing guidelines](https://github.com/ajv-validator/ajv/blob/master/CONTRIBUTING.md)


## Changes history

See https://github.com/ajv-validator/ajv/releases

__Please note__: [Changes in version 7.0.0-beta](https://github.com/ajv-validator/ajv/releases/tag/v7.0.0-beta.0)

[Version 6.0.0](https://github.com/ajv-validator/ajv/releases/tag/v6.0.0).

## Code of conduct

Please review and follow the [Code of conduct](https://github.com/ajv-validator/ajv/blob/master/CODE_OF_CONDUCT.md).

Please report any unacceptable behaviour to ajv.validator@gmail.com - it will be reviewed by the project team.


## Open-source software support

Ajv is a part of [Tidelift subscription](https://tidelift.com/subscription/pkg/npm-ajv?utm_source=npm-ajv&utm_medium=referral&utm_campaign=readme) - it provides a centralised support to open-source software users, in addition to the support provided by software maintainers.


## License

[MIT](https://github.com/ajv-validator/ajv/blob/master/LICENSE)