Unsupported Media Type

4xx · Client Error

Overview

415 Unsupported Media Type means the server rejected the request because the body's format (Content-Type) is not one it supports. For example, sending XML or text/plain to an endpoint that only accepts JSON triggers it.

Where 406 Not Acceptable is about failed negotiation of the response (what the server produces), 415 is about the format of the request body (what the client sends).

When it happens

Sending XML or form-data to a JSON API
The Content-Type header is missing or does not match the actual body
Using a Content-Encoding (e.g. an unusual compression) the server does not support

Request / Response example

Request

POST /api/users HTTP/1.1
Host: api.example.com
Content-Type: text/xml

<user><name>Kim</name></user>

Response

HTTP/1.1 415 Unsupported Media Type
Accept-Post: application/json
Content-Type: application/json

{"error":"unsupported_media_type","expected":"application/json"}

In code

app.post('/api/users', (req, res) => {
  if (!req.is('application/json')) {
    return res.status(415)
      .set('Accept-Post', 'application/json')
      .json({ error: 'unsupported_media_type' });
  }
  // ...
});

curl -X POST https://api.example.com/api/users \
  -H 'Content-Type: application/json' \
  -d '{"name":"Kim"}'

Common causes

A wrong or missing Content-Type header
Sending the body in a format the endpoint does not accept
Using an unsupported Content-Encoding (compression)

How to fix

Set the exact Content-Type the endpoint expects (e.g. application/json)
Convert the body to a format the server supports before sending
Check the allowed formats in the response's Accept-Post header or the API docs

Notes

A common mistake is forgetting Content-Type: application/json when POSTing JSON via fetch — verify the header is set first.
A bad parameter like charset or boundary can also trigger 415, so inspect the entire Content-Type value.