# Configure linting rules

Configure the rules for API linting in the `redocly.yaml` configuration file.

You can add rules, change their severity, or turn them off completely.
Some rules support additional configuration.

You can also provide per-format or even per-API rule configuration.
Use these approaches when your different types of API, or individual APIs, have different linting requirements.

## Simple rule configuration

The following example shows rules configured in `redocly.yaml` with short syntax using the format `rule-name: {severity}`, where `{severity}` is one of `error`, `warn` or `off`:


```yaml
rules:
  operation-operationId: warn
```

Some rules support additional configuration options. The following example shows the more verbose format where the `severity` setting is added alongside other settings:


```yaml
rules:
  path-excludes-patterns:
    severity: error
    patterns:
      - ^\/fetch
      - ^\/v[0-9]
```

Check the documentation for each rule to see if it supports additional configuration.

## Per-API configuration

You can set different rules for individual APIs by adding a `rules` object under each API in `apis`.


```yaml
rules:
  operation-operationId: error
apis:
  museum:
    root: ./apis/museum.yaml
    rules:
      info-license: warn
  tickets@beta:
    root: ./apis/tickets.yaml
    rules:
      info-license: error
      operation-operationId-url-safe: error
      operation-operationId-unique: error
```

Each API picks up the settings that relate to it and gets linted accordingly.

## Per-API configuration with configurable rules

You can use configurable rules for individual APIs.
In the following example, `UserApi@1` has a configurable rule defined.
This rule applies only to `UserApi@1`.

redocly.yaml
extends:
  - recommended

apis:
  partnerApi@1:
    root: partners.yaml
    rules:
      no-server-trailing-slash: off
      operation-operationId: off

  newsletter@3:
    root: /absolute/path/to/folder/openapi.yaml
    extends:
      - minimal
    rules:
      no-server-trailing-slash: off

  UserApi@1:
    root: users.yaml
    rules:
      no-server-trailing-slash: off
      operation-operationId: warn
      assert/version-semver:
        subject:
          type: Info
          property: version
        assertions:
          pattern: /1.[0-9]\.[0-9]/
        message: API version must be in SemVer format, no major version release

## Resources

- Learn more about [rules and rulesets](/docs/cli/v1/rules).
- Check the list of [built-in rules](/docs/cli/v1/rules/built-in-rules).