The 1xx class indicates the server has received the request headers and the client should proceed. Bodies are not returned. Most clients handle these automatically.
Table of 1xx Codes
| Code | Name | Summary |
|---|---|---|
| 100 | Continue | Client may send the request body. |
| 101 | Switching Protocols | Protocol upgrade agreed (e.g., HTTP → WebSocket). |
| 102 | Processing | Server has accepted the request, still working (WebDAV). |
| 103 | Early Hints | Hints for preload before final response (RFC 8297). |
100 Continue
Used with Expect: 100-continue. Lets large uploads avoid sending a body if the server will reject the request.
101 Switching Protocols
Returned when Upgrade: is negotiated (e.g., Upgrade: websocket). Control moves to the new protocol.
102 Processing
WebDAV: indicates the server is still processing. Rare on public websites.
103 Early Hints
Carries Link: rel=preload headers so the client can fetch critical assets sooner. Final 2xx/3xx/4xx/5xx follows.
CDN note: some CDNs pass 103 through; ensure it doesn’t break cache keys or TLS early data.