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HTTP 417 Expectation Failed

Updated Free mock REST & WebSocket APIs

HTTP 417 Expectation Failed — The server can't meet the requirement in the request's Expect header.

Class
4xx Client Error
Defined in
RFC 9110 §15.5.18
Official
Yes (IANA registry)
Cacheable by default
No (unless Cache-Control/Expires say so)
Safe to retry
Not without changing the request

Try it: get a real 417 response

Our test endpoint answers every request with 417 Expectation Failed.

curl -i https://mockfox.dev/api/status/417

Use it in tests, health-check monitors or to see how your client handles a 417. Add ?delay=2000 to slow it down.

What does HTTP 417 mean?

Almost always about Expect: 100-continue: some proxies and older servers don't support it and reply 417. In .NET's HttpClient set ExpectContinue = false; with curl, disable the header with -H "Expect:".

How to fix 417

  1. Visitors: Reload the page, check the address for typos, and clear the site's cookies. If it persists, the site owner needs to fix it.
  2. Developers: Read the response body and server logs for details, fix the request (method, headers, body, credentials) and return a clear error message to clients.

Example 417 response

HTTP/1.1 417 Expectation Failed
Content-Type: application/json

{"status":417,"error":"Expectation Failed"}

4xx Client Error: The request contains an error or can't be fulfilled — fix the request before retrying. See the full list of HTTP status codes.

Related status codes

Related tools

Frequently asked questions

What does HTTP 417 Expectation Failed mean?

The server can't meet the requirement in the request's Expect header.

Is 417 a client or a server error?

417 is a 4xx code, so it signals a problem with the request (as seen by the server). Retrying the identical request usually gives the same result.

Where is 417 defined?

In RFC 9110 §15.5.18. It's listed in the IANA HTTP Status Code Registry.

How can I test how my app handles a 417?

Call https://mockfox.dev/api/status/417 — it responds with 417 to any method, with CORS enabled. Add ?delay=2000 to simulate a slow response.