Measures latency the only way a browser can: the Worker sends a handful of small HTTP requests (no-cors HEAD by default, which works against any reachable HTTPS host without CORS headers) and times each round trip with a high-resolution clock, then reports min, median, average, max, jitter and loss. The first probe includes DNS, TCP and TLS setup and is marked; the warm-connection figures exclude it. Switch to cors mode for servers that allow it to see status codes. This is not ICMP ping: numbers include the server's HTTP handling and are a floor for what an app on this page would see. Probes stop when the Worker's time budget is spent.