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1xx Informational

100 Continue

The server got the request headers and the client can send the body.

What 100 means

Sent in reply to a request with an Expect: 100-continue header. The client asks first before uploading a large body, and the server says "go ahead". HTTP libraries handle this automatically; you rarely see it.

Common causes

  • The client sent Expect: 100-continue before a large upload (curl does this for bodies over 1 MB).

How to fix it

If you're calling an API

  • Nothing to do: keep sending the body. If an API mishandles it, remove the Expect header (curl: -H 'Expect:').

If you run the server

  • Most servers handle it automatically. Reply 417 if you won't accept the body.

Should you retry?

Not applicable: it's an interim response.

Example response

HTTP
HTTP/1.1 100 Continue

Related headers: Expect.

Defined in: RFC 9110 (HTTP Semantics). 100 is a informational.

HTTP 100 FAQ

What does HTTP 100 mean?

100 Continue: The server got the request headers and the client can send the body. Sent in reply to a request with an Expect: 100-continue header. The client asks first before uploading a large body, and the server says "go ahead". HTTP libraries handle this automatically; you rarely see it.

Is 100 a client or server error?

Neither: 100 is a informational response (1xx). Interim responses: the request was received and processing continues.

How do I fix a 100 error?

Nothing to do: keep sending the body. If an API mishandles it, remove the Expect header (curl: -H 'Expect:').

Should I retry after a 100?

Not applicable: it's an interim response.

Other 1xx status codes

All HTTP status codes