HTTP 100 Continue

What Does HTTP 100 Mean?

HTTP 100 Continue is an informational status code indicating that the initial part of a request has been received and the client should continue sending the rest of the request body. The server sends this response to indicate that the request headers have been accepted.

This status code is used with the Expect: 100-continue request header. When a client plans to send a large request body, it first sends the headers with this expectation. The server can then decide whether to accept the request before the client transmits the full body, saving bandwidth if the request would be rejected.

HTTP 100 is transparent to most users and applications. It is handled automatically by HTTP libraries and browsers as part of the protocol handshake.

Common Causes of 100 Continue

The client sends an Expect: 100-continue header with a large request body. The server evaluates the headers before the body is sent. If the headers are acceptable, the server sends 100 Continue.

This typically occurs automatically in HTTP libraries when sending large POST/PUT requests. The client waits for the 100 response before sending the body to avoid wasting bandwidth on requests that would be rejected.

How to Fix 100 Continue

HTTP 100 is handled automatically by HTTP clients and requires no user action. If you're developing an HTTP client library, ensure you handle the 100-continue mechanism correctly by waiting for the server's response before sending large request bodies.

If your server is not sending 100 Continue responses when expected, check that the Expect header handling is properly configured.

Related Status Codes

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