Conditional · Request header

If-None-Match

Send the resource only if its ETag has changed.

What is If-None-Match?

If-None-Match asks the server to return the resource only if its current ETag differs from the one the client cached. Otherwise the server responds with 304 Not Modified and no body.

Typical usage

Sent automatically by browsers when re-requesting a cached resource with an ETag.

Examples

If-None-Match: "33a64df5-e4d42a"

Specification

RFC 9110 §13.1.2

Related headers

ETag

A version identifier for the resource — the backbone of conditional GETs.

If-Modified-Since

Send the resource only if it changed after this date.

Cache-Control

Directives that control caching behavior.

Last-Modified

When the resource was last modified.