HTTP 100 Continue
Updated Free mock REST & WebSocket APIs
HTTP 100 Continue — The server received the request headers and the client should go ahead and send the body.
- Class
- 1xx Informational
- Defined in
- RFC 9110 §15.2.1
- Official
- Yes (IANA registry)
What does HTTP 100 mean?
Sent in reply to a request carrying Expect: 100-continue, so a client can check that a large upload will be accepted (auth, size limits) before transmitting the body. curl sends that header automatically for POST bodies over 1 MB. If the server would reject the request it answers with a final status such as 401 or 413 instead.
Handling 100
- Visitors: You'll never see this in a browser — it's an interim response handled automatically before the final status.
- Developers: Your HTTP client handles 1xx responses internally; fetch() never exposes them. Inspect them with
curl -vor a packet capture.
Example 100 response
HTTP/1.1 100 Continue
1xx Informational: Interim responses: the request was received and processing continues. See the full list of HTTP status codes.
Related status codes
- 101 Switching ProtocolsThe server agrees to switch to the protocol the client asked for in the Upgrade header.
- 417 Expectation FailedThe server can't meet the requirement in the request's Expect header.
- 413 Content Too LargeThe request body is larger than the server is willing to accept.
Related tools
Frequently asked questions
What does HTTP 100 Continue mean?
The server received the request headers and the client should go ahead and send the body.
Is 100 an error?
No. 100 is an informational interim response; a final status follows.
Where is 100 defined?
In RFC 9110 §15.2.1. It's listed in the IANA HTTP Status Code Registry.