Keyboard test
Press every key. Keys light while held and stay marked once seen; double-typing and stuck keys are flagged.
Isolation: —
Click the board or Start capturing, then press keys. To leave, use Stop capturing or hold Esc for one second.
Key marks:corner mark — reported at least oncesolid — held nowdashed frame — release not reportedhatched — sends no events
An input method (IME) is active and hides key codes. Switch it off while testing.
- Held now
- —
- Most at once
- —
- Presses
- —
- Chatter
- —
Result
Waiting for input
Loading the instrument…
This keyboard test lights every key you press on an ANSI, ISO, JIS or ABNT2 layout and flags the common faults: keys that type twice (a re-press within 30 ms without auto-repeat), keys that never register, and keys stuck down for more than 10 seconds. Press every key once; 50 presses give a verdict.
How to read the readings
| Reading | Pass | Marginal | Fault |
|---|---|---|---|
| Chatter (re-press < 30 ms or press < 5 ms) | 0 | 1–2 | 3 or more |
| Stuck | — | — | held over 10 s |
| Most at once | as many as the board promises | — | — |
What a browser cannot measure
- Fn never reaches the browser; its cap is hatched.
- The OS keeps Win, Alt+Tab and Ctrl+Alt+Del. In Chrome, “Capture system keys” takes some of them back in full screen.
- macOS sends no key-up for keys released while Cmd is held; they are marked unknown.
- Keyboard polling rate and latency cannot be measured from key events.
Fixing the fault
Windows
- Turn off Filter Keys (Settings → Accessibility → Keyboard).
- Clean under the keycap; on hot-swap boards, reseat or replace the switch.
macOS
- Check Accessibility → Keyboard → Slow Keys is off.
- Clean under the keycap or replace the switch.
Linux
evtestshows whether the key reaches the kernel.
Questions
Why does the Fn key not light up?
Fn is handled inside the keyboard and never reaches the computer as a key event.
Why does a key type twice?
The switch bounces: it reports a second press within a few milliseconds. Cleaning can help; otherwise replace the switch.
Why are some keys marked unknown on a Mac?
macOS does not report releasing a key while Cmd is held. Those keys are reset when Cmd is released and marked as unknown.
Method and algorithm version
Algorithm version 1 (2026-10). Keys are identified by KeyboardEvent.code; legends come from navigator.keyboard.getLayoutMap() in Chromium, otherwise from the layout default of the page language.