HTTP 417 Expectation Failed means the server cannot meet the expectation specified in the request's Expect header. This most commonly occurs when a server does not support the Expect: 100-continue mechanism.
Status
417 Expectation FailedExample
Request
POST /upload HTTP/1.1
Host: www.example.com
User-Agent: Mozilla/5.0
Accept: text/html
Expect: 100-continue
Content-Length: 1048576Response
HTTP/1.1 417 Expectation Failed
Content-Type: text/html; charset=utf-8
<!doctype html>
<html>
<body>
<h1>417 Expectation Failed</h1>
<p>The server cannot meet the conditions specified in your request.</p>
</body>
</html>How to Troubleshoot
1
Remove the Expect header
Send the request without the Expect header.
curl -H 'Expect:' -X POST -d @file.dat https://example.com/upload
2
Check proxy compatibility
Some proxies strip or reject the Expect header. Test against the origin directly to isolate the issue.
Common Causes
Server does not support Expect: 100-continue
highThe client sent Expect: 100-continue but the server or proxy does not support interim responses.
Related Status Codes
References
| Specification | Section |
|---|---|
| HTTP Semantics | RFC 9110 §15.5.18 |
Frequently Asked Questions
This reference was compiled from official RFCs, protocol specifications, and hands-on troubleshooting experience. AI tools were used primarily for formatting and organizing the content on the page.