100 Continue

What it means

The server has received the request headers and the client should proceed to send the body. It exists for the Expect: 100-continue handshake, which lets clients avoid uploading large bodies the server would reject anyway.

Common causes

• Client sent Expect: 100-continue before uploading a large body
• Some clients (incl. cURL for >1KB bodies) add it automatically

Reproduce it in cURL

curl -v -H "Expect: 100-continue" -d @bigfile.json https://httpbin.org/post

Same request, no terminal: paste this into the cURL converter for native code, or straight into ReqPad on your phone.

How to debug it

Seen mostly with large uploads via cURL or HTTP clients that set Expect: 100-continue automatically.

The fastest way to pin down a 100 is to reproduce the exact request and inspect what actually went over the wire — status, headers, timing and body, without your app code in the way. That is what an API client is for; ReqPad does it from your phone, with every request saved to history.

Related codes

101 Switching Protocols · 102 Processing · 103 Early Hints — or the full reference.