> For the complete documentation index, see [llms.txt](https://eazyapi-1.gitbook.io/docs/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://eazyapi-1.gitbook.io/docs/open-api-guide/openapi-extensions.md).

# OpenAPI Extensions

Extensions (also referred to as *specification extensions* or *vendor extensions*) are custom properties that start with `x-`, such as `x-logo`. They can be used to describe extra functionality that is not covered by the standard OpenAPI Specification. Many API-related products that support OpenAPI make use of extensions to document their own attributes, such as Amazon API Gateway, ReDoc, APIMatic and others. Extensions are supported on the root level of the API spec and in the following places:

* `info` section
* `paths` section, individual paths and operations
* operation parameters
* `responses`
* `tags`
* security schemes

The extension value can be a primitive, an array, an object or `null`. If the value is an object or array of objects, the object’s property names do not need to start with `x-`.

### Example

An API that uses Amazon API Gateway custom authorizer might include extensions similar to this:

{% code lineNumbers="true" %}

```yaml
components:
  securitySchemes:
    APIGatewayAuthorizer:
      type: apiKey
      name: Authorization
      in: header
      x-amazon-apigateway-authtype: oauth2
      x-amazon-apigateway-authorizer:
        type: token
        authorizerUri: arn:aws:apigateway:us-east-1:lambda:path/2015-03-31/functions/arn:aws:lambda:us-east-1:account-id:function:function-name/invocations
        authorizerCredentials: arn:aws:iam::account-id:role
        identityValidationExpression: "^x-[a-z]+"
        authorizerResultTtlInSeconds: 60
```

{% endcode %}