DevToolsmith

HTTP 417 Expectation Failed

HTTP 417 Expectation Failed means the server can’t meet the requirement in the Expect header. The request contains an error or can’t be fulfilled. Retrying unchanged won’t help.

Class
4xx Client error
Standard
RFC 9110
Cacheable by default
No
Safe to retry
No
Go constant
http.StatusExpectationFailed

What HTTP 417 means

The only defined expectation is Expect: 100-continue. Some servers and proxies don’t support it and reply 417. Older .NET HttpClient and PHP curl requests often run into this with certain proxies.

How to fix a 417 error

  • Disable the header: curl -H "Expect:", or ServicePointManager.Expect100Continue = false in .NET Framework.

Retrying

No. Fix the request first; sending it again unchanged will get the same response.

Example response

HTTP/1.1 417 Expectation Failed
Date: Wed, 21 Oct 2026 10:30:00 GMT
Content-Type: application/json

How to return 417

Node.js (Express)
res.status(417).json({ error: 'Expectation Failed' });
Python (FastAPI)
from fastapi import HTTPException

raise HTTPException(status_code=417, detail="Expectation Failed")
Go (net/http)
http.Error(w, http.StatusText(http.StatusExpectationFailed), http.StatusExpectationFailed)
nginx
location /private/ {
    return 417;
}

Related status codes

Other 4xx status codes

400 Bad Request · 401 Unauthorized · 402 Payment Required · 403 Forbidden · 404 Not Found · 405 Method Not Allowed · 406 Not Acceptable · 407 Proxy Authentication Required · 408 Request Timeout · 409 Conflict · 410 Gone · 411 Length Required · 412 Precondition Failed · 413 Content Too Large · 414 URI Too Long · 415 Unsupported Media Type · 416 Range Not Satisfiable · 418 I’m a Teapot · 421 Misdirected Request · 422 Unprocessable Content · 423 Locked · 424 Failed Dependency · 425 Too Early · 426 Upgrade Required · 428 Precondition Required · 429 Too Many Requests · 431 Request Header Fields Too Large · 444 No Response · 451 Unavailable For Legal Reasons · 499 Client Closed Request

See the full list of HTTP status codes.

Sources

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Frequently asked questions

What does HTTP 417 Expectation Failed mean?

HTTP 417 Expectation Failed means the server can’t meet the requirement in the Expect header. The only defined expectation is Expect: 100-continue. Some servers and proxies don’t support it and reply 417. Older .NET HttpClient and PHP curl requests often run into this with certain proxies.

How do I fix HTTP 417?

Disable the header: curl -H "Expect:", or ServicePointManager.Expect100Continue = false in .NET Framework.