HTTP 417 Expectation Failed vs 431 Request Header Fields Too Large
Both HTTP 417 (Expectation Failed) and 431 (Request Header Fields Too Large) belong to the 4xx Client Error category. 417 indicates that the server cannot meet the requirements of the Expect header. Meanwhile, 431 means that the server refuses to process the request because an individual header field or all headers collectively are too large.
Description
The server cannot meet the requirements of the Expect header.
When You See It
When the server doesn't support Expect: 100-continue.
How to Fix
Remove the Expect header from your request.
Description
The server refuses to process the request because an individual header field or all headers collectively are too large.
When You See It
When cookies accumulate to an excessive size, or a single header (like Authorization) is too long.
How to Fix
Reduce header sizes. Clear excessive cookies. Use shorter tokens.
Key Differences
HTTP 417: The server cannot meet the requirements of the Expect header.
HTTP 431: The server refuses to process the request because an individual header field or all headers collectively are too large.
You encounter 417 when when the server doesn't support Expect: 100-continue.
You encounter 431 when when cookies accumulate to an excessive size, or a single header (like Authorization) is too long.
When to Use Which
For 417 (Expectation Failed): Remove the Expect header from your request. For 431 (Request Header Fields Too Large): Reduce header sizes. Clear excessive cookies. Use shorter tokens.