HTTP headers / response header

Last-Modified

Last-Modified: Tue, 10 Jun 2026 18:31:00 GMT

What it does

Timestamp-based cache validator, the simpler sibling of ETag. Pairs with If-Modified-Since.

The gotcha

One-second resolution makes it unreliable for fast-changing resources — prefer ETag when both exist.

Debugging headers on a phone

The fastest way to see what Last-Modified is actually doing is to send the request and read both sides raw — ReqPad shows auto-generated and custom headers for every request, on all six protocols, with history. Related references: status codes · WWW-Authenticate · Content-Encoding · Transfer-Encoding · ETag · Expires · Location

Inspect Last-Modified on a live request.

Build the request, send it, read raw headers and timing — from your iPhone. Free to start.

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