411 Error

A 411 Length Required error is a webserver’s code for:

“You didn't tell me how large this upload is, and I refuse to accept it blind.”

A 411 Length Required error occurs when the server refuses to accept a request without a defined Content-Length header.

When uploading files or sending data via POST or PUT requests, webservers rely on the Content-Length header to know exactly how many bytes to read and how much buffer space to allocate. If this header is missing, the server sends a 411 response to protect itself from buffer overruns.

Determining why

Standard web browsers automatically calculate and send Content-Length headers when submitting forms. This error is almost always encountered by developers writing custom API scripts, curl commands, or automated web scrapers that omit length headers during chunked uploads.

Steps you could possibly take:

  • If you are a website visitor - Ensure your browser is up to date and try disabling aggressive browser extensions that intercept or strip network headers.
  • If you are a developer or API client:
    • Add a valid Content-Length header specifying the size of the request body in octets (bytes).
    • If using curl, avoid raw socket streaming without length parameters or supply -H "Content-Length: ...".
    • If using chunked transfer encoding, verify whether the destination server or reverse proxy supports HTTP/1.1 chunked requests without an explicit length.

Source: RFC 9110 Section 15.5.12 (HTTP Semantics)