HTTP 417 Expectation Failed

What does HTTP 417 mean?

The server cannot meet the requirement in the request’s Expect header. Almost always about Expect: 100-continue, which curl and .NET send before uploading large bodies. Some proxies and old servers reject it.

4xx Client error: The request has a problem the client can fix: wrong URL, missing credentials, bad data or too many requests.

Common causes of a 417 error

• A proxy or server that does not support Expect: 100-continue.
• An HTTP client sending Expect to an endpoint that does not allow it.

How to fix 417 Expectation Failed

• Disable the header in the client: curl -H "Expect:", or in .NET set ServicePointManager.Expect100Continue = false.
• Upgrade or reconfigure the proxy in front of the server.

417 and SEO

No SEO impact: browsers don’t send Expect for page loads.

Example response

HTTP/1.1 417 Expectation Failed

How to return a 417 response

Node.js (Express)

res.status(417).json({ error: 'Expectation Failed' });

PHP

http_response_code(417);

Python (Flask)

return {'error': 'Expectation Failed'}, 417

Go (net/http)

w.WriteHeader(417)

nginx

return 417;

Related status codes

• 100 Continue — The server has received the request headers and the client may send the body.
• 400 Bad Request — The server cannot process the request because it is malformed.
• 413 Content Too Large — The request body is larger than the server allows.

Check which status code a URL returns with the HTTP header checker.