How to use it· 4 steps
- Click the capture box, or Tab to it and press Enter. Keys are read only while it says Capturing.
- Press every key once. Each turns green when it works; one that stays grey did not register.
- Hold several keys together to test rollover, and watch Most at once.
- Press Esc twice, click Stop capturing or click anywhere else to finish. Reset starts over.
Step by step
How to use the keyboard tester
- 1Click the capture box, or Tab to it and press Enter. Keys are read only while it says Capturing.
- 2Press every key once. Each turns green when it works; one that stays grey did not register.
- 3Hold several keys together to test rollover, and watch Most at once.
- 4Press Esc twice, click Stop capturing or click anywhere else to finish. Reset starts over.
What the colours mean
Grey is a key that has not sent anything yet. Green means the key works: the browser received its press or its release. Blue means it is held down right now, which is how a stuck key shows itself — one that stays blue after you let go is still reporting "down". An amber ring marks chatter: a key that registered twice within 50 milliseconds, faster than any finger can press it.
Choose ANSI or ISO to match your keyboard. ANSI is the US layout, with a wide single-row Enter and a long left Shift. ISO is used across the UK and most of Europe: a tall L-shaped Enter, a short left Shift with an extra key beside it, and another extra key next to Enter — which is why an ISO board has 105 keys to ANSI's 104. Japanese JIS boards have more keys again; they are not drawn, but every press still appears in the event panel.
Rollover and ghosting, explained
A keyboard does not wire each key to the computer separately. The switches sit where the rows and columns of a grid cross, and a controller scans that grid many times a second to find which crossings are closed. Hold three keys at three corners of a rectangle in the grid and current can flow round through them, making the fourth corner look pressed as well — a ghost key.
Cheaper keyboards avoid ghosts by refusing to register any key that could create one, called blocking or jamming: the third or fourth key of certain combinations simply does nothing. That is why a game can ignore a jump while you hold forward and sideways. Keyboards with a diode on every switch cannot ghost at all and can report any number of keys at once — N-key rollover, or NKRO.
To test it, hold keys one after another — A, S, D, F, then J, K, L — and watch Most at once. When a key stops lighting up, you have found the limit for that combination; try others, because the limit varies across the grid, and gaming keyboards often guarantee rollover only around WASD. Many USB keyboards report at most six ordinary keys plus the modifiers, because that is all the basic USB boot-keyboard report holds; NKRO boards use a different report, sometimes switched on with a key combination.
key, code and keyCode
The event panel shows exactly what the browser receives. key is the character or action produced, after your operating system's layout and the Shift state are applied: a, A, Enter, ArrowUp. code is the physical position, regardless of layout — the key to the right of Caps Lock is KeyA whether it types a, q on a French AZERTY board, or ф on a Russian one. The drawing is keyed on code for that reason: it is the switch being tested, not the layout.
keyCode and which are older numeric codes, now deprecated, that plenty of games, scripts and tutorials still read: A is 65, Enter 13, Escape 27, Space 32, the left arrow 37. Browsers disagree about them on non-US layouts, which is why they were replaced, but when you are debugging old code they are what it sees.
location tells apart keys that exist twice: 1 is the left Shift, Ctrl, Alt or Windows/Command key, 2 the right one, 3 the numeric keypad and 0 everything else. repeat is true for the automatic repeats sent while a key is held down.
Keys that never reach a web page
Some keys cannot be tested in any browser. Fn is handled inside the keyboard and sends no event of its own — it changes what other keys send. The operating system keeps certain shortcuts for itself, such as Alt+Tab, Ctrl+Alt+Delete and Windows-key combinations on Windows, or ⌘Tab and ⌘Space on a Mac, and media, volume and brightness keys are often consumed by the system before a page sees them.
Three platform quirks are handled so they are not mistaken for faults. On Windows, browsers usually see only the release of Print Screen, which is enough to count it. On a Mac, Caps Lock reports a press when it turns on and a release when it turns off, so it is treated as a toggle, and keys released while ⌘ is held never report their release, so letting go of ⌘ clears them.
Making sense of what you find
A key that stays grey however you press it is not registering: try another USB port, and give a wireless keyboard fresh batteries. A key that works only when pressed hard or dead centre usually has debris under the cap or a worn membrane.
Chatter — double letters while typing — is common on mechanical keyboards as switches age or collect dust. Compressed air sometimes clears it; otherwise the switch needs replacing, which takes minutes on a hot-swap board. If keys light up in the right place but type the wrong characters, the hardware is fine and the operating system's keyboard layout is set wrongly.
Capturing safely
While capturing, the tester stops keys doing their usual jobs, so Tab, Space, the arrows and the function keys can be tested without the page scrolling or focus jumping away. It does this only inside the marked box, and only after you start capture there with a click or Enter — moving onto the box with Tab does not trap the Tab key. Esc twice, Stop capturing or a click elsewhere always gets you out.
Answers
Frequently asked questions
How many keys can my keyboard press at once?
Hold keys one after another and watch Most at once. Some office keyboards manage two or three in certain combinations, basic USB mode allows six plus modifiers, and NKRO keyboards register every key.
Why doesn't the Fn key light up?
Fn is handled inside the keyboard and never sends a key event, so no web page or program can see it. It changes what the other keys send instead.
What is the difference between key and code?
key is the character produced under your layout and Shift state; code is the physical position. On a French keyboard, the key right of Caps Lock has the key value q and the code KeyA.
Why is Tab not moving between links?
Because the tester is capturing, and Tab is being tested rather than used. Press Esc twice or click Stop capturing, and Tab works normally again.
What is keyboard chatter?
A worn or dirty switch reading one press as two, which types double letters. The tester flags any key that registers twice within 50 milliseconds — something a finger cannot do.
Does it record what I type?
No. Key events are shown on screen and go nowhere else — nothing is stored or sent, and Reset clears it all.
Does it work on laptops and phones?
On a laptop, yes, including the built-in keyboard. On a phone or tablet it needs a physical keyboard, because on-screen keyboards do not report key positions.