Testing starts when this page opens. Choose ANSI, ISO or JIS and Mac or Windows labels, then inspect every key, repeat behavior, suspicious double typing, browser-observed rollover, CPS and event timing.
Keystrokes are processed locally and are never sent to Jemdo. Do not type passwords while testing.
No. It can show the simultaneous key events it received, but operating-system and browser shortcuts may hide some combinations.
No. A web page can report event cadence and browser scheduling delay, but it cannot isolate the keyboard scan, USB polling, operating-system queue and display latency into a true hardware measurement.
It means two key-down events arrived unusually close together after a release. Repeated warnings on the same key can indicate a worn or dirty switch; one warning may simply be a fast intentional tap.
Only a short local event log is held in memory for the visible test. Nothing is uploaded, and Reset removes it.
macOS may handle media and brightness actions before the browser. Try the enhanced F-key capture button, which uses fullscreen Keyboard Lock where supported, or hold Fn or Globe while pressing the key. You can also enable standard function keys in macOS Keyboard settings. Fn itself may still remain invisible because macOS does not always send it to web pages.