406 Not Acceptable

What it means

HTTP 406 Not Acceptable means the request carried Accept headers describing the content types, languages, or encodings the client is willing to take, and the server has nothing that fits. Rather than send a format the client cannot use, it refuses. In practice most servers ignore the mismatch and send their best guess, so a genuine 406 is uncommon.

When it happens

It happens when an API client demands a specific representation — say Accept: application/xml — from an endpoint that only speaks JSON, or when strict content negotiation rules on the server have no acceptable match for the request.

How to fix it

• Relax or correct the client's Accept headers so they include a format the server can return.
• Check the server's content-negotiation configuration to confirm it offers the representations clients expect.
• For an API, document the media types each endpoint supports so callers ask for the right one.

SEO impact

Rare for indexable pages. Crawlers send permissive Accept headers, so 406 seldom blocks them, but any page that returns it cannot be indexed.