406

Not Acceptable

4xx Client Error

ELI5

I can't give you the data in the format you want. I have the data, but not in XML/JSON/etc. that you asked for.

Server perspective

Use 406 when the client's proactive negotiation constraints leave no representation you are willing to serve.

When to use

•Return 406 when Accept, Accept-Language, or Accept-Encoding excludes every available representation
•Use it when you do not want to fall back to a default representation
•Client requests unsupported response format
•Accept header specifies unavailable content types
•Language negotiation fails
•Encoding negotiation fails

How to respond

•List the available representations or supported values when that helps the client recover
•Keep 406 distinct from 415, which is about the request payload format

Headers to consider

•No status-specific header is required; still send normal HTTP metadata such as Content-Type, caching, or tracing headers when they help the client.

Response body

•Include available representation formats when that helps the client adjust Accept headers.

Server-side pitfalls

•Do not use 406 for unsupported request Content-Type
•Do not send 406 if serving a documented default representation is acceptable for your API
•Request media type unsupported (use 415 Unsupported Media Type)
•Resource doesn't exist (use 404 Not Found)
•Bad request format (use 400 Bad Request)

Examples

Unsupported response format

Request:

GET https://api.example.test/api/data

# Headers
Accept: application/xml

Response:

406 Not Acceptable

# Headers
Content-Type: application/json

# Body
{
  "available": [
    "application/json"
  ]
}

API only supports JSON responses, not XML

References

Related Status Codes

Unsupported Media Type

I don't understand the format of data you sent me. Please send it as JSON, XML, or another format I support.