# schema-format-unknown

Source: https://apigenie.pl/docs/linter/swagger/rules/schema-format-unknown

This rule reports a `format` of a Swagger 2.0 document which is neither in the
[OpenAPI format registry](https://spec.openapis.org/registry/format/) nor
declared in `openapi.custom_formats` of the
[configuration file](/docs/reference/cli/configuration#openapicustom_formats).

## Rule Details

Tools ignore formats they don't know, so a misspelled format (`date_time`,
`uuid4`) silently stops being checked. Formats defined on purpose are declared
in the configuration file:

```yaml
openapi:
  custom_formats:
    - {name: currency-code, type: string}
```

The rule is off in the `recommended` ruleset and a warning in `strict` and
`all`. See [Formats](/docs/reference/cli/formats) for the registry's
formats.

## Configuration

None.

## When Not to Use It

When the documents use many formats of their own and listing them in the
configuration file isn't worth it.