411 Length Required means the server refuses to accept the request without a defined Content-Length. The client may repeat the request with a valid Content-Length header that gives the size of the body.
It happens with POST and PUT requests that send their body with chunked transfer encoding to a server that does not accept it, and with requests that have no body and no Content-Length: 0. Some large services, Google among them, answer an empty POST without Content-Length with 411.
Example response
HTTP
HTTP/1.1 411 Length Required
Date: Fri, 06 Nov 2026 10:15:32 GMT
Content-Type: text/html; charset=UTF-8
Content-Length: 66
Connection: close
<p>POST requests require a <code>Content-length</code> header.</p>SEO and redirect checking
Crawlers fetch pages with GET, which has no body, so 411 has no SEO impact. In a redirect check it can appear when you use POST: when a 307 or 308 is followed, the request body and its length must be sent again.
Common causes and use cases
- An HTTP client sends a
POSTwithout a body and withoutContent-Length: 0. - A streaming upload uses
Transfer-Encoding: chunked, and the server or a proxy requires a length. - A proxy removes or rewrites the
Content-Lengthheader.