# parameters-unique

Source: https://apigenie.pl/docs/linter/openapi/rules/parameters-unique

Check parameters of operations and path items and warn if they have duplicate
parameters.

## Rule Details

If an operation or a path item defines multiple parameters with the same
location and name, this signals an error.

This `parameters-unique` rule checks parameters of every path item and every
operation in OpenAPI schema and warns if any of them has parameters with the
same name and location.

## Configuration

None.

## Examples

**Good**. Parameters are unique.

```yaml
paths:
  /users/{id}:
    get:
      parameters:
        - name: id
          in: path
          description: The ID of the user to retrieve.
          required: true
          schema:
            type: string
        - name: with-relations
          in: query
          description: If true, also returns related resources.
          required: false
          schema:
            type: boolean
```

**Good**. While parameter names are identical, their locations are not.

```yaml
paths:
  /users/{id}:
    get:
      parameters:
        - name: id
          in: path
          description: The ID of the user to retrieve.
          required: true
          schema:
            type: string
        - name: id
          in: query
          description: Controversial, but still OK.
          required: false
          schema:
            type: boolean
```

**Bad**. Duplicate parameter definitions lead to confusion, which most likely
is an error.

```yaml
paths:
  /users/{id}:
    get:
      parameters:
        - name: id
          in: path
          description: The ID of the user to retrieve.
          required: true
          schema:
            type: string
        - name: id
          in: path
          description: The ID of the user to retrieve.
          required: true
          schema:
            type: boolean
```

## When Not to Use It

We recommend to always enable this rule.

## Automatic fixes

When invoked with `--fix`, this rule removes a later duplicate only when its
complete source definition is structurally identical to the first definition.
Conflicting duplicate parameters remain manual.

## Compatibility

This rule is compatible with all OpenAPI 3.x versions.