# Allow header > Lists the HTTP methods supported by the target resource, on a 405 Method Not Allowed or a 2xx OPTIONS response. Source: https://apiguide.dev/headers/allow Direction: response Registered: yes Defined in: RFC 9110, Section 10.2.1 Updated: 2026-07-09 ## What is the Allow header? The `Allow` response header lists the set of HTTP methods supported by a resource. It is required on any `405 Method Not Allowed` response, and is equally standard on a successful `OPTIONS` response, where it's the primary way a client discovers what a resource supports. ## API Usage & Best Practices * **Always send on 405**: When rejecting a request due to an unsupported method, always include `Allow: GET, POST, HEAD` (matching the supported methods for that path). * **Also send on OPTIONS**: A `200 OK` response to `OPTIONS` should carry the same header so clients can probe supported methods without triggering an error. * **Do not include trailing commas**: The methods should be comma-separated, like `GET, POST, PUT`. ## Examples ```http HTTP/1.1 405 Method Not Allowed Allow: GET, HEAD Content-Type: application/problem+json ```