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4xx Client Error

417 Expectation Failed

The server cannot meet the expectation in the request's Expect header. In practice this means that Expect: 100-continue is not supported.

Category
4xx Client Error
Reason phrase
Expectation Failed
Specification
RFC 9110, Section 15.5.18 (opens in a new tab)
Redirect
No
Cacheable by default
No

417 Expectation Failed means that at least one of the servers handling the request cannot meet the expectation given in its Expect header. The only expectation HTTP defines is 100-continue, so in practice a 417 means a server or proxy does not support it.

The fix is usually on the client side: repeat the request without the Expect header and send the body directly. Some HTTP clients do this automatically when they receive 417.

Example response

HTTP
HTTP/1.1 417 Expectation Failed
Date: Fri, 06 Nov 2026 10:15:32 GMT
Connection: close
Content-Length: 0

SEO and redirect checking

No SEO impact, since crawlers do not send Expect headers. In a redirect check, 417 only appears if you add an Expect header to the request.

Common causes and use cases

  • A client, such as curl for larger uploads, sends Expect: 100-continue to a server or proxy that does not support it.
  • An old proxy rejects every Expect header it does not understand.
  • The client sent an expectation value that is not defined.

Related status codes

All HTTP status codes

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