411 - Length Required
HTTP 411 Length Required means the server requires a defined Content-Length for this request.
Last reviewed: April 16, 2026|Source-backed guidance under our editorial policy
Start Here
Use the closest compare guide, playbook, or adjacent error page to narrow the decision faster before you start changing production systems.
This page is part of the Error Reference library. Learn more about the project or report a correction.
What Does Length Required Mean?
The server rejects this body-bearing request before processing because message length is not explicitly provided in the form this endpoint requires.
Common Causes
- -Client sends chunked body without Content-Length, but upstream requires fixed length for request signing logic.
- -Gateway policy enforces Content-Length on POST and PUT for quota accounting and rejects missing header.
- -Upload service pre-allocates buffers from declared length, so absent Content-Length fails early validation.
How to Fix Length Required
- 1Send an accurate
Content-Lengthfor body-bearing requests when endpoint policy requires it. - 2Ensure transport layers do not drop or rewrite length metadata during retries and proxy hops.
- 3If streaming is required, verify server and intermediaries support the chosen framing model consistently.
Step-by-Step Diagnosis for Length Required
- 1Capture raw request bytes and verify
Content-Lengthheader presence, format, and numeric accuracy. - 2Compare client framing behavior with gateway/origin rules for body-bearing methods.
- 3Inspect intermediaries for transfer transformations that invalidate or remove declared length.
- 4Retest with a small deterministic payload and validated
Content-Lengthcalculation.
Message Framing and Length Integrity
- -Verify header length matches actual payload byte count (example: UTF-8 body counted as characters instead of bytes causes mismatch).
- -Check request-building libraries for late body mutations after length is computed (example: middleware appends JSON field post-serialization).
Proxy and Transfer-Encoding Compatibility
- -Trace proxy behavior that strips
Content-Lengthduring replay or buffering (example: edge retry path removes length header on POST). - -Audit
Transfer-EncodingversusContent-Lengthhandling consistency (example: origin requires fixed length, intermediary converts to chunked stream).
Implementation Examples
curl -i -X POST https://api.example.com/v1/resource -H "Content-Type: application/json" -d "{"sample":true}"
# Response:
# HTTP/1.1 411 Length Required
# {"error":"Length Required","code":"411"}const response = await fetch('https://api.example.com/v1/resource', {
method: 'POST',
headers: { 'Content-Type': 'application/json', 'Accept': 'application/json' },
body: JSON.stringify({ sample: true })
});
if (response.status === 411) {
console.error('Handle 411 Length Required');
}import requests
response = requests.post(
'https://api.example.com/v1/resource',
headers={'Accept': 'application/json', 'Content-Type': 'application/json'},
json={'sample': True}
)
if response.status_code == 411:
print('Handle 411 Length Required')Seen in Production
Custom client sends streamed POST without explicit length
Frequency: common
Example: Internal integration built on raw sockets omits Content-Length, and origin policy rejects request with 411.
Fix: Buffer payload before send or switch to a client library that calculates and sets Content-Length automatically.
Retry path through one proxy strips framing metadata
Frequency: rare
Example: Direct traffic succeeds, but failover path removes Content-Length on retried POST and triggers 411 only during incident mode.
Fix: Align proxy retry configuration across regions and test raw header preservation in failover drills.
Debugging Tools
- -Raw header capture with byte-size breakdown
- -Gateway/proxy header-limit rejection logs
- -Browser cookie inspection tools
- -Header-budget regression tests in CI
How to Verify the Fix
- -Repeat the request and confirm 411 is cleared when length metadata is valid and preserved.
- -Validate body framing behavior across direct, proxied, and retried request paths.
- -Monitor parser errors for residual length/framing mismatches after rollout.
How to Prevent Recurrence
- -Use client libraries that consistently set Content-Length for buffered payloads.
- -Add gateway regression tests for framing and Content-Length preservation.
- -Alert on spikes in length-related request parsing failures.
Pro Tip
- -serialize payload once, freeze the byte buffer, and compute
Content-Lengthfrom that immutable buffer to avoid race-condition mismatches.
Official References
Provider Context
This guidance is specific to HTTP services. Always validate implementation details against official provider documentation before deploying to production.