I Built a One File Edge Probe to Tell Me When Time Is Lying

This is also why I lean on a tiny JSON route with simple CORS. For anyone wiring this up, they can add

Access-Control-Allow-Origin: * (or site origin), and Cache-Control: no-store

Also, watch for mixed content (HTTPS page trying to fetch HTTP gateway), either serve the probe from the gateway or expose /time over HTTPS.

Yes, many servers don’t expose Date to browsers (Access-Control-Expose-Headers), so you can’t read it cross-origin. Also, CDNs/proxies can cache or rewrite headers, my goal was a boring, local /time on the same gateway the tech is testing. Another thing was that Date is seconds-resolution, I want ms and a stable JSON shape. I have found Cloudflare trace to be handy in past, but it’s not my box, it may rate-limit, and adds an extra network hop. For the core question "Is it me or the edge box" I wanted the box itself to answer.