Keyboard test (rollover and chatter)

See which keys reach the browser, how many you can hold at once, and keys that register twice too quickly. Runs in your browser.

A physical keyboard is needed. On-screen phone keyboards do not report keys the same way, so results are not meaningful there.

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How to use

Press “Start testing”. While testing, page shortcuts are suspended; Esc stops it.
Choose the JIS or US picture. The lights follow the physical key (the same key in either picture).
Hold several keys to see the largest number held at once.
Set the chatter window (ms). A key pressed again sooner than that after its previous press is logged as a chatter suspect.

Worked example

Example: with a 50 ms window, pressing A at 1,000 ms and again at 1,030 ms (with a release in between) is logged as a 30 ms suspect. A normal re-type 200 ms later is not.

Limits

Keys the OS or browser keeps for itself (for example the Windows key, Alt+Tab, Ctrl+W, Fn keys on many laptops) cannot be seen.
The maximum number held is what the browser received. The keyboard, the connection and the OS can limit it (6-key rollover, shared matrix lines).
A fast legitimate double tap looks like chatter. The log is a hint, not a diagnosis; try a few different windows and repeat.
Auto-repeat events are ignored.

Your inputs and results stay in this browser. Nothing is sent to a server.