Why would an empty POST get 411?
Some servers require a Content-Length on every POST, even when the body is empty. Sending Content-Length: 0 explicitly satisfies them.
HTTP 411 LENGTH REQUIRED
The server needs a Content-Length header. 411 belongs to the 4xx client error class and is defined in RFC 9110.
Loading the workbench.
About HTTP 411
What Does HTTP 411 Length Required Mean?
The server needs a Content-Length header. 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 411 must treat it like 400.
When Do You See a 411 Response?
411 Length Required means the server insists on a Content-Length header and refuses requests without one. It mostly appears when a client sends a body with chunked transfer encoding to a server or proxy that does not accept it, or sends a POST with no body and no Content-Length. Some older servers and storage APIs reject chunked uploads entirely because they need to know the size up front.
How Do You Fix a 411?
Clients should send a Content-Length header with the exact size of the body in bytes, including Content-Length: 0 on empty POST or PUT requests. Buffer the body first if the library streams it with chunked encoding by default. Remember that Content-Length counts bytes, not characters, so multi-byte UTF-8 text makes it larger than the string length.
What Does a 411 Response Look Like?
HTTP/1.1 411 Length Required
Connection: close
Content-Length: 0411 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 411?
- 413 Content Too Large: The body is bigger than the server accepts. Formerly "Payload Too Large".
- 400 Bad Request: The request is malformed: bad syntax, invalid framing, or an unreadable body.
- 415 Unsupported Media Type: The server does not accept this Content-Type or Content-Encoding.
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
Does HTTP/2 ever return 411?
Rarely. HTTP/2 frames bodies itself, so Content-Length is optional there, but a server or gateway can still demand it before accepting an upload.
Is HTTP 411 an error?
Yes. 411 is a client error response: the problem is in the request, so repeating it unchanged will usually fail again.
Is a 411 response cacheable by default?
No. Caches store a 411 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.