HTTP 100 Continue vs 425 Too Early
HTTP 100 (Continue) is a 1xx Informational response, while 425 (Too Early) is a 4xx Client Error response. 100 indicates that the server has received the request headers and the client should proceed to send the request body. This lets the client know it can continue with the request or abort if the headers were rejected. In contrast, 425 means that the server is unwilling to risk processing a request that might be replayed. Used with TLS 1.3 early data (0-RTT).
Description
The server has received the request headers and the client should proceed to send the request body. This lets the client know it can continue with the request or abort if the headers were rejected.
When You See It
When a client sends an Expect: 100-continue header, the server responds with 100 before the client sends the body.
How to Fix
This is an interim response — no fix needed. The client should continue sending the request body.
Description
The server is unwilling to risk processing a request that might be replayed. Used with TLS 1.3 early data (0-RTT).
When You See It
When a server rejects a request sent as TLS 1.3 early data due to replay risk.
How to Fix
Retry the request after the TLS handshake completes.
Key Differences
100 is a 1xx Informational response, while 425 is a 4xx Client Error response.
HTTP 100: The server has received the request headers and the client should proceed to send the request body. This lets the client know it can continue with the request or abort if the headers were rejected.
HTTP 425: The server is unwilling to risk processing a request that might be replayed. Used with TLS 1.3 early data (0-RTT).
You encounter 100 when when a client sends an Expect: 100-continue header, the server responds with 100 before the client sends the body.
You encounter 425 when when a server rejects a request sent as TLS 1.3 early data due to replay risk.
When to Use Which
For 100 (Continue): This is an interim response — no fix needed. The client should continue sending the request body. For 425 (Too Early): Retry the request after the TLS handshake completes.