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HTTP/4xx (Client Error)

417 Expectation Failed

The server cannot meet the requirements of the Expect request header.

❓ Why does this happen?

Client (often curl or .NET HttpClient) sends Expect: 100-continue to a proxy that does not support it.

✅ How to fix it

Disable the Expect header, for example: curl -H "Expect:" ...

Return or handle 417 in your stack

// app/api/resource/route.ts
export function GET() {
  return Response.json(
    { error: "Expectation Failed", status: 417 },
    {
      status: 417
    }
  );
}

Live 417 mock endpoint

Point your app, tests, or retry logic at this free public URL to reproduce a real 417 response (CORS enabled, optional ?delay=ms up to 5000).

https://castov.com/api/mock/417

Frequently Asked Questions

What does HTTP Status 417 mean?
The server cannot meet the requirements of the Expect request header.
Why am I getting a 417 status code?
Client (often curl or .NET HttpClient) sends Expect: 100-continue to a proxy that does not support it.
How do I fix a 417 Expectation Failed error?
Disable the Expect header, for example: curl -H "Expect:" ...
How can I test how my app handles a 417 response?
Send a request to https://castov.com/api/mock/417 — it returns a real 417 Expectation Failed response with CORS enabled. Add ?delay=2000 to simulate a slow server.

Other 4xx status codes

400401402403404405406407408409410411412413414415416417418421422423425426428429431451499

Browse the full HTTP status codes directory or troubleshoot terminal errors in the Error Fix Encyclopedia.