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.