- _hostname_: host name according to [RFC1034](http://tools.ietf.org/html/rfc1034#section-3.5).
- _ipv4_: IP address v4.
- _ipv6_: IP address v6.
- _regex_: tests whether a string is a valid regular expression by passing it to RegExp constructor.
- _uuid_: Universally Unique IDentifier according to [RFC4122](http://tools.ietf.org/html/rfc4122).
- _json-pointer_: JSON-pointer according to [RFC6901](https://tools.ietf.org/html/rfc6901).
- _relative-json-pointer_: relative JSON-pointer according to [this draft](http://tools.ietf.org/html/draft-luff-relative-json-pointer-00).
See regular expressions used for format validation and the sources that were used in [formats.ts](https://github.com/ajv-validator/ajv-formats/blob/master/src/formats.ts).
**Please note**: JSON Schema draft-07 also defines formats `iri`, `iri-reference`, `idn-hostname` and `idn-email` for URLs, hostnames and emails with international characters. These formats are available in [ajv-formats-draft2019](https://github.com/luzlab/ajv-formats-draft2019) plugin.
## Keywords to compare values: `formatMaximum` / `formatMinimum` and `formatExclusiveMaximum` / `formatExclusiveMinimum`
These keywords allow to define minimum/maximum constraints when the format keyword defines ordering (`compare` function in format definition).
Rhese keywords are added to ajv instance when ajv-formats is used without options or with option `keywords: true`.
These keywords apply only to strings. If the data is not a string, the validation succeeds.
The value of keywords `formatMaximum`/`formatMinimum` and `formatExclusiveMaximum`/`formatExclusiveMinimum` should be a string or [\$data reference](https://github.com/ajv-validator/ajv/blob/master/docs/validation.md#data-reference). This value is the maximum (minimum) allowed value for the data to be valid as determined by `format` keyword. If `format` keyword is not present schema compilation will throw exception.
When these keyword are added, they also add comparison functions to formats `"date"`, `"time"` and `"date-time"`. User-defined formats also can have comparison functions. See [addFormat](https://github.com/ajv-validator/ajv/blob/master/docs/api.md#api-addformat) method.
Options can be passed via the second parameter. Options value can be
1. The list of format names that will be added to ajv instance:
```javascript
addFormats(ajv, ["date", "time"])
```
**Please note**: when ajv encounters an undefined format it throws exception (unless ajv instance was configured with `strict: false` option). To allow specific undefined formats they have to be passed to ajv instance via `formats` option with `true` value:
```javascript
const ajv = new Ajv((formats: {date: true, time: true})) // to ignore "date" and "time" formats in schemas.
```
2. Format validation mode (default is `"full"`) with optional list of format names and `keywords` option to add additional format comparison keywords:
In `"fast"` mode the following formats are simplified: `"date"`, `"time"`, `"date-time"`, `"uri"`, `"uri-reference"`, `"email"`. For example `"date"`, `"time"` and `"date-time"` do not validate ranges in `"fast"` mode, only string structure, and other formats have simplified regular expressions.