Not Acceptable

Overview

406 Not Acceptable is returned when the server cannot produce a response in a format required by the request's Accept-family headers — that is, content negotiation failed.

For example, if the client allowed only Accept: application/xml but the server can only produce JSON, no representation satisfies the constraint, so it responds 406.

When it happens

• It is returned when the client's Accept header demands only media types the server cannot produce.
• It can also occur when Accept-Language or Accept-Encoding is so restrictive that the server finds no representation to satisfy it.

Request / Response example

GET /api/report HTTP/1.1
Host: api.example.com
Accept: application/xml

HTTP/1.1 406 Not Acceptable
Content-Type: application/json

{"error":"not_acceptable","supported":["application/json"]}

In code

app.get('/api/report', (req, res) => {
  if (!req.accepts('json'))
    return res.status(406).json({ supported: ['application/json'] });
  res.json(report);
});

Notes

• Many servers pragmatically return a default format (such as JSON) on negotiation failure instead of 406, so 406 is relatively rare.
• When the request body's format is unsupported (an upload-side problem), 415 Unsupported Media Type is correct, not 406.
• Remember the direction: 406 is a failure to negotiate the response format the server produces, while 415 is about the request format the server accepts.

Related status codes

Related headers

Specification