KeyboardTest is a free, single-purpose tool: a full-size on-screen keyboard that lights each key as you press it. It’s built for anyone diagnosing a keyboard — a gamer checking rollover before a tournament, a buyer testing a second-hand board, a laptop owner whose E key just died, or a developer who needs the exact code/key/keyCode triple a keystroke produces.

What the tester shows

• Per-key state — amber while held, shaded once tested, red when a key is held long enough to look stuck.
• The raw event — event.code, event.key, event.keyCode, event.which and event location for every keystroke, the same values a developer would read in DevTools.
• Rollover counters — live held-count and the maximum simultaneous presses your board managed, plus a held-keys strip so you can see exactly which of your pressed keys were reported.
• A press history — the last 40 key events as chips, so a key that flickers in and out leaves a trail.
• ANSI and ISO layouts — including the L-shaped ISO Enter and the extra <> key beside left Shift.

How the detection works

Everything runs in your browser. The page listens for the standard keydown/keyup events the OS delivers and maps each event.code to a keycap — that’s why it can show the physical key position regardless of what character your layout prints. Nothing is sent anywhere: there is no backend, no account, and your key presses are never logged by us.

One deliberate design choice: the tester only intercepts keys that would otherwise scroll the page or open browser UI — F-keys, arrows, Tab, Space — and only while the tester is focused or your pointer is over it. Ctrl/⌘ shortcuts always pass through.

Who maintains it

KeyboardTest is maintained by a small independent team that builds focused utility sites. Found a key that behaves strangely, a layout we should add, or a bug in the detection? Contact us — hardware-quirk reports get answered first.