All HTTP status codes

HTTP 100 Continue

Informational

The server received the request headers and the client should proceed to send the request body. Used with the Expect: 100-continue header on large uploads.

Defined in RFC 9110

Common causes

  • Client sent an Expect: 100-continue header before a large upload
  • Reverse proxy negotiating a request body transfer

How to fix it

  1. Nothing to fix — proceed with sending the body

  2. If uploads stall, check whether a proxy strips or mishandles the Expect header

Related status codes

101 Switching Protocols

The server agrees to switch to the protocol the client requested in the Upgrade header — most commonly seen when establishing a WebSocket connection.

417 Expectation Failed

The server can't meet the requirements of the Expect header (almost always Expect: 100-continue).

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