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HTTP Status Code
406 Not Acceptable
Client ErrorThe server cannot generate a response matching the values in the request Accept headers.
HTTP status code reference, response example, common causes, fixes, and related status codes.
What does HTTP 406 Not Acceptable mean?
HTTP 406 Not Acceptable is a status code sent by a server to indicate the result of an HTTP request.
Status codes help browsers, APIs, apps, and backend systems understand whether a request succeeded, failed, was redirected, or needs additional action.
In practice, HTTP 406 Not Acceptable usually appears when a server responds under specific request, validation, permission, or infrastructure conditions.
Response example
HTTP/1.1 406 Not Acceptable
HTTP example
HTTP/1.1 406 Not Acceptable
Relevant headers
Accept
Accept: application/json
Common causes
- Unsupported response format requested
- Incorrect Accept header
How to fix it
- Adjust the Accept header
- Return a supported content type from the server
Common mistakes
- Assuming the status code alone explains the full backend issue
- Ignoring related response headers that add important context
- Treating temporary errors as permanent failures
- Retrying too aggressively without checking the cause
- Debugging the frontend only when the problem is server-side
How browsers and APIs use it
Browsers, APIs, and backend services use HTTP status codes to understand the outcome of a request. Depending on the status code, an application may render content, retry a request, redirect the user, show an error, or trigger a different flow in the client or server.
Developer note
HTTP 406 is less common than 415, but it can appear when content negotiation fails between client and server.