? HTTP 411 – Length Required

? Quick Overview

HTTP 411 Length Required is a client error status code indicating that the server refuses to accept the request without a valid Content-Length header.

? Key Concepts

The server requires the Content-Length header.
Common with POST, PUT, or PATCH requests.
Mostly occurs in strict or legacy HTTP servers.
Related to request body size validation.

? Syntax / Theory

When a client sends a request with a body, the server may require the exact size of that body. If the header is missing, the server responds with 411 Length Required.

? Code Example(s)

? View Code Example

// HTTP request missing Content-Length header POST /api/data HTTP/1.1 Host: example.com Content-Type: application/json {"name":"Alex"}

? Live Output / Explanation

Server Response

The server rejects the request and responds with:

? View Response

// Server requires Content-Length header HTTP/1.1 411 Length Required Content-Type: text/plain Length Required

? Interactive Simulator

Toggle the Content-Length header below and "Send" the request to see how the server reacts.

Include Content-Length header?

? Use Cases

Debugging API requests from low-level clients
Working with custom HTTP libraries
Legacy server environments
Understanding strict HTTP compliance

✅ Tips & Best Practices

Let browsers or libraries handle headers automatically.
Always include a request body size when building raw HTTP requests.
Use tools like Postman or curl carefully.

? Try It Yourself

Create a raw HTTP POST request without Content-Length.
Send it to a strict server endpoint.
Add the header manually and compare results.