What is the difference between 406 and 415?
406 is about the response: the server cannot produce a type the client accepts. 415 is about the request: the server cannot consume the Content-Type the client sent.
HTTP 406 NOT ACCEPTABLE
No representation matches the Accept headers the client sent. 406 belongs to the 4xx client error class and is defined in RFC 9110.
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About HTTP 406
What Does HTTP 406 Not Acceptable Mean?
No representation matches the Accept headers the client sent. The code is registered with IANA and defined in RFC 9110.
Client error: the request has a problem, so it cannot be fulfilled as sent. Every code from 400 to 499 shares that general meaning, so a client that does not recognise 406 must treat it like 400.
When Do You See a 406 Response?
406 Not Acceptable is the result of proactive content negotiation failing: the client's Accept, Accept-Language, or Accept-Encoding headers ruled out every representation the server can produce. A typical case is an API client sending Accept: application/xml to a JSON-only service. Some web application firewalls also misuse 406 to block requests they dislike, which can be confusing because nothing about the Accept headers is wrong.
How Do You Fix a 406?
Clients should loosen their Accept header, for example add */*;q=0.1, or request a type the server documents. Servers can list the available representations in the body. Many servers simply ignore Accept and send their default representation with a 200, which RFC 9110 allows and is usually friendlier. If a WAF is the source, check its logs for the rule that fired.
What Does a 406 Response Look Like?
HTTP/1.1 406 Not Acceptable
Content-Type: application/json
Vary: Accept406 is not cacheable by default: a browser or CDN stores it only when Cache-Control or Expires explicitly allows it.
To inspect a real one without sending it anywhere:
- Copy the response headers from your browser Network tab, or from
curl -i. - Paste them into the Header decoder to see every header explained.
- Check caching in the Cache lane.
Which Status Codes Are Related to 406?
- 415 Unsupported Media Type: The server does not accept this Content-Type or Content-Encoding.
- 300 Multiple Choices: Several representations are available and the client may choose.
- 400 Bad Request: The request is malformed: bad syntax, invalid framing, or an unreadable body.
Browse every code on the HTTP status codes page.
What Other Lanes Are in the Reference Section?
- HTTP status codes: Every IANA-registered status code, with a page per code.
- MIME types: File extensions to Content-Type, searchable both ways, plus a Content-Type parser.
- HTTP methods: GET, POST, PUT, PATCH, DELETE and the rest: safe, idempotent, cacheable.
Elsewhere in 2http: Header decoder, Cookie decoder, Cache-Control decoder, CORS checker, User-agent parser, and all eleven lanes on the 2http home page. Part of the 2suite.io privacy-first ecosystem.
Frequently Asked Questions
Must a server return 406 when Accept does not match?
No. It may instead send its default representation with 200. Many servers do, because a usable response is usually better than an error.
Is HTTP 406 an error?
Yes. 406 is a client error response: the problem is in the request, so repeating it unchanged will usually fail again.
Is a 406 response cacheable by default?
No. Caches store a 406 only when Cache-Control or Expires explicitly allows it.
How Can You Verify That Nothing Leaves This Browser?
You do not have to take our word that your headers stay here. Developer tools show every request a page makes, so you can watch this page work and confirm that nothing is sent. The check takes under a minute.
- Open your browser developer tools with
F12, orCmd+Option+Ion a Mac, and select the Network tab. - Reload the page and let it finish. You will see the page's own files, its web fonts, and one anonymous page-view request. Nothing has been typed yet, so none of them can contain your headers.
- Click the clear icon in the Network tab so that the log is empty.
- Paste real headers into any lane and read the result.
- Look at the Network tab again. It is still empty. For extra proof, turn on offline mode after the page loads and every lane keeps working.
Only two things can add a line to that log, and neither carries your headers. Submitting the feedback form sends the vote and comment you typed. Typing characters in a script the page has not displayed yet, such as Cyrillic or Greek, can make the browser fetch the matching font file, and that request names only the font.
2http never sends a request on your behalf: the request builder writes code for you to run, and the meta inspector reads source you paste instead of fetching a URL. The production site also sends a Content-Security-Policy header that tells your browser to refuse connections to anywhere except this site and the anonymous analytics endpoint.