A keyboard tester shows, key by key, exactly what your keyboard sends to the computer — invaluable when QA-testing a new mechanical board, diagnosing a key that "sometimes doesn't work," or checking a used keyboard before you rely on it. Press any key and this tool lights up the matching key on an on-screen layout.

It reads each key by its physical position (the browser's event.code), so it identifies the exact key regardless of your layout or language. A rollover counter shows how many keys register at once — the quick way to test n-key rollover (NKRO) and find out whether your board drops inputs during the fast, multi-key combinations that gaming and touch-typing demand.

It also surfaces flaky switches: if a single press registers twice (chatter, a debounce failure) or a key won't light at all, you've found the fault. Everything runs locally in the browser — no install, nothing sent anywhere.