100 Continue

What does 100 Continue mean?

The server received the request headers and the client should proceed to send the request body. It belongs to the 1xx Informational class, which means the request was received and the process is continuing. These are interim responses you rarely handle directly.

When do APIs return 100?

A client sent an Expect: 100-continue header before uploading a large body, asking the server whether it is worth sending.

How to fix a 100 Continue

Nothing to fix — this is an interim response. Most HTTP libraries handle it transparently and you will rarely see it surface in an API tester.

Reproduce a 100 response

The fastest way to understand a status code is to trigger one and read the full response. Open the API tester and send a request to https://httpbin.org/status/100 — you will see the 100 status along with every response header the server sent. Comparing those headers against a working request is often what reveals the cause.

When you are debugging a real endpoint, check the response headers as carefully as the body, and confirm you are using the right HTTP method for the operation.

Related 1xx status codes