Continue
1xx Informational
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The initial part of a request has been received and the client can proceed with the request body.
Description
Sent in response to an Expect: 100-continue header from the client. It signals that the request can proceed without a body being rejected outright. Modern HTTP libraries handle this transparently; you rarely emit it manually.
When to use
Return 100 when your endpoint accepts large uploads and you want the client to defer sending the body until the server has validated the request headers (e.g. authentication, size limits).
Specification
RFC 9110 §15.2.1
Examples
HTTP response
HTTP/1.1 100 Continue
Content-Type: application/json
{"error":"Continue"}Node.js (Express)
res.status(100).json({ error: "Continue" });Go (net/http)
w.WriteHeader(http.StatusContinue)
Python (Flask)
return jsonify({"error": "Continue"}), 100