415 Unsupported Media Type: the request body format is wrong

415 Unsupported Media Type means the server won’t accept the request body because of its format. You sent form data to an endpoint that expects JSON, forgot the Content-Type header, or used a compression the server can’t decode.

Definition

RFC 9110, section 15.5.16 says the problem can come from the request’s Content-Type, its Content-Encoding, or from the server inspecting the data directly. When an unsupported content coding is the cause, the response should include an Accept-Encoding header listing the codings it does accept. For PATCH, RFC 5789 defines Accept-Patch to list supported patch formats.

Don’t confuse it with 406 Not Acceptable: 415 is about what the client sends, 406 about what it’s willing to receive.

Common causes

• A missing or wrong Content-Type, such as application/x-www-form-urlencoded or text/plain sent to a JSON API. Frameworks such as Spring and ASP.NET Core reject these with 415.
• An upload in a file type the endpoint doesn’t accept.
• A gzip-compressed request body sent to a server that doesn’t decompress requests.
• JavaScript fetch() calls that send JSON.stringify(data) without setting the header, so the body goes out as text/plain.

How to fix it

# curl: declare the JSON body
curl -X POST https://api.example.com/v1/contacts \
  -H 'Content-Type: application/json' \
  -d '{"email":"sara@example.com"}'

// fetch()
fetch('/api/v1/contacts', {
  method: 'POST',
  headers: { 'Content-Type': 'application/json' },
  body: JSON.stringify({ email: 'sara@example.com' })
});

On the server, return a message that names the accepted types so integrators can fix their call quickly.

SEO impact

Crawlers don’t send request bodies, so 415 has no direct effect on indexing. It does turn up in SEO work through APIs: submitting URLs to IndexNow by POST, for instance, needs a JSON body with the right header, which the IndexNow submitter handles for you. If a normal page returns 415 to a GET, it’s a server bug; Google would treat it as a 4xx and drop the page. Check pages with the HTTP status checker.

Example

POST /api/v1/contacts HTTP/1.1
Host: api.example.com
Content-Type: text/plain

email=sara@example.com

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

{"error":"Expected Content-Type: application/json"}

Frequently asked questions