`type` keyword requires that the data is of certain type (or some of types). Its value can be a string (the allowed type) or an array of strings (multiple allowed types).
Most other keywords apply only to a particular type of data. If the data is of different type, the keyword will not apply and the data will be considered valid.
## Keywords for numbers
### `maximum` / `minimum` and `exclusiveMaximum` / `exclusiveMinimum`
The value of keyword `maximum` (`minimum`) should be a number. This value is the maximum (minimum) allowed value for the data to be valid.
Draft-04: The value of keyword `exclusiveMaximum` (`exclusiveMinimum`) should be a boolean value. These keyword cannot be used without `maximum` (`minimum`). If this keyword value is equal to `true`, the data should not be equal to the value in `maximum` (`minimum`) keyword to be valid.
Draft-06/07: The value of keyword `exclusiveMaximum` (`exclusiveMinimum`) should be a number. This value is the exclusive maximum (minimum) allowed value for the data to be valid (the data equal to this keyword value is invalid).
The value of the keyword should be a number. The data to be valid should be a multiple of the keyword value (i.e. the result of division of the data on the value should be integer).
The value of the keywords should be a number. The data to be valid should have length satisfying this rule. Unicode pairs are counted as a single character.
The value of keyword `formatMaximum` (`formatMinimum`) should be a string. This value is the maximum (minimum) allowed value for the data to be valid as determined by `format` keyword.
The value of keyword `formatExclusiveMaximum` (`formatExclusiveMinimum`) should be a boolean value. These keyword cannot be used without `formatMaximum` (`formatMinimum`). If this keyword value is equal to `true`, the data to be valid should not be equal to the value in `formatMaximum` (`formatMinimum`) keyword.
The value of the keyword should be an object or an array of objects.
If the keyword value is an object, then for the data array to be valid each item of the array should be valid according to the schema in this value. In this case the "additionalItems" keyword is ignored.
If the keyword value is an array, then items with indices less than the number of items in the keyword should be valid according to the schemas with the same indices. Whether additional items are valid will depend on "additionalItems" keyword.
The value of the keyword should be a boolean or an object.
If "items" keyword is not present or it is an object, "additionalItems" keyword is ignored regardless of its value.
If "items" keyword is an array and data array has not more items than the length of "items" keyword value, "additionalItems" keyword is also ignored.
If the length of data array is bigger than the length of "items" keyword value than the result of the validation depends on the value of "additionalItems" keyword:
- an object: data is valid if all additional items (i.e. items with indices greater or equal than "items" keyword value length) are valid according to the schema in "additionalItems" keyword.
The value of the keywords should be a number. The data object to be valid should have not more (less) properties than the keyword value.
__Example__
_schema_: `{ "maxProperties": 2 }`
_valid_: `{}`, `{"a": 1}`, `{"a": "1", "b": 2}`, any non-object
_invalid_: `{"a": 1, "b": 2, "c": 3}`
### `required`
The value of the keyword should be an array of unique strings. The data object to be valid should contain all properties with names equal to the elements in the keyword value.
The value of the keyword should be a map with keys equal to data object properties. Each value in the map should be a JSON Schema. For data object to be valid the corresponding values in data object properties should be valid according to these schemas.
The value of this keyword should be a map where keys should be regular expressions and the values should be JSON Schemas. For data object to be valid the values in data object properties that match regular expression(s) should be valid according to the corresponding schema(s).
When the value in data object property matches multiple regular expressions it should be valid according to all the schemas for all matched regular expressions.
If the value is `false` the data object to be valid should not have "additional properties" (i.e. properties other than those used in "properties" keyword and those that match patterns in "patternProperties" keyword).
If the value is a schema for the data object to be valid the values in all "additional properties" should be valid according to this schema.
The value of the keyword is a map with keys equal to data object properties. Each value in the map should be either an array of unique property names ("property dependency") or a JSON Schema ("schema dependency").
For property dependency, if the data object contains a property that is a key in the keyword value, then to be valid the data object should also contain all properties from the array of properties.
For schema dependency, if the data object contains a property that is a key in the keyword value, then to be valid the data object itself (NOT the property value) should be valid according to the schema.
The value of this keyword should be an array of strings, each string being a regular expression. For data object to be valid each regular expression in this array should match at least one property name in the data object.
If the array contains multiple regular expressions, more than one expression can match the same property name.
The same can be achieved with `enum` keyword using the array with one item. But `const` keyword is more than just a syntax sugar for `enum`. In combination with the [$data reference](https://github.com/epoberezkin/ajv#data-reference) it allows to define equality relations between different parts of the data. This cannot be achieved with `enum` keyword even with `$data` reference because `$data` cannot be used in place of one item - it can only be used in place of the whole array in `enum` keyword.
The value of the keyword should be an array of JSON Schemas. The data is valid if it matches exactly one JSON Schema from this array. Validators have to validate data against all schemas to establish validity according to this keyword.
The value of the keyword should be an array of JSON Schemas. The data is valid if it is valid according to one or more JSON Schemas in this array. Validators only need to validate data against schemas in order until the first schema matches (or until all schemas have been tried). For this reason validating against this keyword is faster than against "oneOf" keyword in most cases.
If the data is valid against the sub-schema in `if` keyword, then the validation result is equal to the result of data validation against the sub-schema in `then` keyword (if `then` is absent, the validation succeeds).
If the data is invalid against the sub-schema in `if` keyword, then the validation result is equal to the result of data validation against the sub-schema in `else` keyword (if `else` is absent, the validation succeeds).
