Status codes · 1xx–5xx
1xx: 100 Continue, 101 and 103 Early Hints
Distinguish interim responses, protocol switching and early resource hints.
Understand the concept
An exchange can contain informational responses before its final response. With Expect: 100-continue, a client can wait before sending a large body. A server may return 100 to let transmission proceed or reject early. Actual waiting behaviour depends on the client and its timeout. Receiving 100 does not mean an upload was stored successfully; the final response still decides that.
101 belongs to HTTP/1.1 protocol switching, commonly seen in a classic WebSocket upgrade. Do not transplant that textual upgrade into HTTP/2 or HTTP/3. Those versions use different mechanisms. 102 is a WebDAV-related interim processing response rather than a general application success.
103 can send resource hints while the final document is being prepared. Support and benefit depend on the browser, framework and proxy path. Excessive preloading wastes bandwidth. Treat hints as an optimisation to measure, and record the final response separately from any interim responses.
When examining large uploads, WebSockets and document loading performance.
Counting 103 or 100 as the transaction’s final success.
One topic. Three levels of depth.
Expect: 100-continue
HTTP/1.1 100 ContinueThis only permits body transmission to continue.
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Try it yourself first.
A log shows 103 followed by 500. Was the request successful?
Show the solution and explanation
Final status: 500No. A resource hint does not change the final processing outcome.