Keyboard Tester
Check every key, test rollover & ghosting (NKRO), catch stuck keys, and debug keybinds — all in your browser.
US ANSI tenkeyless layout shown. Keys not on the diagram (numpad, media keys…) still count and are listed below. Hover a key to see its press count.
While the tester is active, keydown events are intercepted (preventDefault) so nothing scrolls, types or navigates. Escape hatches: press Esc twice quickly to release your keyboard, and F5 / F11 / F12 are never blocked. Everything runs locally — no key data ever leaves your browser.
How to test your keyboard
- Every-key check: press each key once. It flashes bright red while held and stays dimly marked once tested — any key that never lights up is dead.
- Rollover (NKRO) test: press and hold as many keys as you can — palms welcome. Held right now is your live count and max at once is your record. Try gaming combos like Shift+W+A+Space+Ctrl.
- Ghosting test: hold 3–4 close-together letters (e.g. Q+W+E, then add R). If a key you're physically holding never lights up, it's being blocked; if a key you're not touching lights up, that's a ghost.
- Stuck-key check: release everything — the held list should empty instantly. Anything that lingers (flagged after 8 s) has a stuck switch or a missed key-up.
- Keybind debugging: the last-event readout shows event.key, event.code, the legacy keyCode, and left/right location — handy when configuring game binds, AutoHotkey or remappers.
Ghosting vs. NKRO in 30 seconds
Rollover is how many simultaneous keys your keyboard can report. Basic office boards guarantee 2 (2KRO), most USB boards do 6 keys + modifiers (6KRO), and NKRO boards report every key independently.
Ghosting comes from the key matrix: without a diode per key, three pressed keys forming an “L” in the wiring grid can look electrically identical to four — so the board either invents a phantom press (a ghost) or, far more commonly, blocks the extra key so your real input is dropped mid-fight. “Anti-ghosting” marketing usually means selective blocking around WASD; true NKRO means nothing is ever dropped. This tester shows both failure modes directly: blocked keys never light up, ghosts light up on their own.
FAQ
What is key rollover (NKRO)?
Rollover is how many keys your keyboard can register at the same time. A 2KRO board guarantees any 2 keys, 6KRO guarantees any 6, and NKRO (n-key rollover) means every key registers independently no matter how many you hold. Gaming keyboards advertise NKRO so combos like Shift+W+A+Space never drop an input.
What is keyboard ghosting?
Keyboards wire keys in a grid (matrix). On cheap boards without per-key diodes, holding three keys that form an L-shape in the matrix can make the electronics see a phantom fourth key you never pressed — a ghost. To avoid sending ghosts, most boards instead block (jam) the extra key, so your real keypress is silently dropped. Anti-ghosting and NKRO designs fix this with diodes.
Why does the count stop around 6 keys?
Many keyboards run in the USB boot-protocol mode, which reports at most 6 regular keys plus modifiers (Shift, Ctrl, Alt, Win) at once. Some boards need a special NKRO mode or a driver toggle to go beyond 6. If you hit exactly 6 plus modifiers, that's the protocol limit, not a broken keyboard.
Why don't Fn or some media keys show up?
The Fn key is handled inside the keyboard's own hardware and never reaches the operating system, so no software can see it. Media keys, macro keys and some laptop specials may be intercepted by the OS or drivers before the browser gets an event. The Windows key registers, but the OS may still open the Start menu when you release it.
How do I find a stuck or broken key?
Press every key once — any key that never lights up on the diagram is dead. A stuck key shows the opposite symptom: it appears in the held-keys list (or stays bright red) even after you let go, or shows up as held the moment the tester starts. Keys held longer than 8 seconds are flagged as possibly stuck.