If-None-Match
Request headers
Asks for the resource only if its ETag differs — this is how a cache revalidates.
| On the wire | If-None-Match: … |
|---|---|
| Category | Request headers |
Headers the browser attaches when it sends to the server.
How to read this
- The first digit of a status code carries the meaning: 4 means the request, 5 means the server.
- 404 means "not there"; 403 means "there, but not for you". Swapping them makes debugging slower.
- Header names are case-insensitive — Content-Type and content-type are the same header.
- Caching and CORS problems usually come down to one header line, visible in the browser’s network tab.
Frequently asked questions
QWhat does HTTP If-None-Match mean?
Asks for the resource only if its ETag differs — this is how a cache revalidates.
QWhat does If-None-Match look like on the wire?
It travels as If-None-Match: …
QWhere does If-None-Match appear?
In request headers.
QWhat group does If-None-Match belong to?
The request headers group; the rest of that group is listed further down.