411 Length Required

Meaning & Description

Common Causes

• Missing Content-Length header on a request that contains a body.
• Using Transfer-Encoding: chunked on an endpoint that requires a fixed content length.
• A strict server configuration (like Nginx or HAProxy) rejecting body-less POST requests without a length header.

How to fix a 411 error

1. Check your HTTP client to ensure it automatically calculates and appends the Content-Length header.
2. If sending an empty body, explicitly set `Content-Length: 0`.
3. Verify that intermediate load balancers or proxies are not stripping the header.

Browser & SEO Behaviour

Code Examples

HTTP/1.1 411 Length Required
Content-Type: text/plain
Connection: close

Content-Length header is missing.

app.post("/upload", (req, res) => {
  if (!req.headers["content-length"]) {
    return res.status(411).send("Content-Length header is required.");
  }
  // Process upload...
});

from fastapi import FastAPI, Request, HTTPException

app = FastAPI()

@app.post("/submit")
async def submit_data(request: Request):
    if "content-length" not in request.headers:
        raise HTTPException(status_code=411, detail="Length Required")
    return {"message": "Success"}

func handler(w http.ResponseWriter, r *http.Request) {
    if r.ContentLength == -1 {
        http.Error(w, "Length Required", http.StatusLengthRequired)
        return
    }
    w.WriteHeader(http.StatusOK)
}

[HttpPost("data")]
public IActionResult PostData()
{
    if (!Request.Headers.ContainsKey("Content-Length"))
    {
        return StatusCode(411, "Content-Length header missing");
    }
    return Ok();
}

# Adding Content-Length explicitly for an empty POST
curl -X POST -H "Content-Length: 0" https://api.example.com/trigger

Raw HTTP Response Example

HTTP/1.1 411 Length Required
Date: Wed, 21 Oct 2026 07:28:00 GMT
Content-Type: text/plain; charset=utf-8
Content-Length: 42

Request must include Content-Length header

Real-world Examples

Frequently Asked Questions

Developer Tips

• Always ensure your HTTP client library is up to date, as modern libraries handle Content-Length calculation automatically.
• If proxying requests, be careful not to strip Content-Length headers unless you are deliberately switching to chunked transfer encoding.
• For API endpoints that only trigger actions and do not need a payload, accept POSTs with `Content-Length: 0` gracefully.

Interview Questions

These are questions you might face in a backend or API design interview that touch on HTTP 411.