HTTP 100 Continue vs 304 Not Modified
HTTP 100 (Continue) is a 1xx Informational response, while 304 (Not Modified) is a 3xx Redirection 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, 304 means that the resource has not been modified since the last request. The client can use its cached copy.
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 resource has not been modified since the last request. The client can use its cached copy.
When You See It
When the browser cache is still valid (If-None-Match / If-Modified-Since headers match).
How to Fix
No fix needed. This saves bandwidth by confirming the cached version is still current.
Key Differences
100 is a 1xx Informational response, while 304 is a 3xx Redirection 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 304: The resource has not been modified since the last request. The client can use its cached copy.
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 304 when when the browser cache is still valid (If-None-Match / If-Modified-Since headers match).
When to Use Which
For 100 (Continue): This is an interim response — no fix needed. The client should continue sending the request body. For 304 (Not Modified): No fix needed. This saves bandwidth by confirming the cached version is still current.