Measures download and upload throughput plus connection latency. The test talks directly to Cloudflare speed nodes — no third parties, and no personal data is uploaded.
The test transfers several payload sizes and times them, then takes a stable value to reduce jitter. Do not stream or download while testing; Wi-Fi and mobile networks usually differ a lot, which is normal.
If the result is far below your plan, try another node or another device to rule out your router, cable or the device itself.