Conditional · Response header

Last-Modified

When the resource was last modified.

What is Last-Modified?

Last-Modified provides a date-based version of the resource. Prefer ETag when both are available — ETags are more precise and support content-addressed caching.

Typical usage

Set by most static file servers automatically.

Examples

Last-Modified: Wed, 21 Oct 2025 07:28:00 GMT

Specification

RFC 9110 §8.8.2

Related headers

If-Modified-Since

Send the resource only if it changed after this date.

ETag

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

If-None-Match

Send the resource only if its ETag has changed.