Keyboard Tester | Check Every Key, Ghosting & N-Key Rollover (NKRO)
Free online keyboard tester. Press any key on your keyboard and watch it light up on the on-screen diagram in real time, so you can spot dead keys and check ghosting / N-key rollover (NKRO). Switch between ANSI (US) and JIS layouts. No sign-up, all data stays in your browser.
What is a keyboard tester?
A keyboard tester lets you verify that every key on a computer or gaming keyboard physically registers a press. As you type, the on-screen diagram lights up the matching key, so dead keys or keys that get stuck can be spotted at a glance. It is handy for checking a brand-new keyboard for defects, inspecting a used keyboard before buying, or confirming everything still works after cleaning or disassembly.
This tool also reports how many keys can be detected at the same time. On many budget keyboards, the internal wiring (the key matrix) has physical limits, and pressing certain combinations of keys can cause some of them to go undetected — a phenomenon called ghosting. This matters most in games that require several keys pressed together at once, such as diagonal movement combined with jump and crouch.
How to use the keyboard tester
- Pick your keyboard layout Choose US layout (ANSI) or JIS layout to match your physical keyboard. The number and position of keys shown will change accordingly.
- Press keys one by one Each key you press turns blue on the diagram, and turns green (tested) once you release it. Keys that never change color are not registering.
- Work through the whole keyboard The "Keys tested" count and percentage increase as you go. A completion message appears once every key has been tested.
- Test key combinations together Press a combination you use often (e.g. WASD + Shift + Space) at the same time and check whether "keys currently held down" matches the number you actually pressed.
- Reset and try again if needed The "Reset test" button clears your tested-key history and the recorded maximum simultaneous count so you can start over.
Tips for getting more out of it
- Laptop keyboards sold in different regions can differ in key count and symbol placement between US and JIS layouts, so pick the layout that matches the labels printed on your actual keys.
- Gaming keyboards advertised as "NKRO" are, in theory, able to register every key pressed at once, but the real limit can depend on the USB connection, hub, or wireless dongle in use — testing it directly is exactly what this tool is for.
- If a key produces no reaction at all, a browser extension or an OS-level shortcut may be intercepting it first. Trying an incognito/private window can help rule that out.
- If a single key press is registered inconsistently or repeats on its own, the physical contact may be worn out (a symptom often called chattering); if cleaning does not fix it, that is a sign the key or keyboard needs replacing.
- When checking a used keyboard before buying, first press every key to confirm 100% coverage, then test the specific combinations you actually rely on for ghosting.
When to use this tool
Inspecting a brand-new keyboard
Press every key right after unboxing to check for dead keys or stuck keys before your return window closes.
Checking a used or thrift-store keyboard
Verify full key coverage and the simultaneous-press limit of a second-hand keyboard right after purchase.
Verifying a gaming keyboard's NKRO claim
Confirm whether the advertised "NKRO" or "N-key rollover" support actually holds up in your real setup, such as through a USB hub or a wireless receiver.
Confirming everything works after cleaning
After removing keycaps to clean underneath, run through every key to make sure it still registers correctly.
Comparing US and JIS layouts
If you are considering switching to an imported keyboard, the diagram makes the differences in symbol keys and key count easy to see at a glance.
Keyboard testing terms
- NKRO (N-Key Rollover)
- The ability of a keyboard to correctly register every key pressed simultaneously, regardless of how many. The "N" implies no practical limit, and it is a common selling point for gaming keyboards.
- Ghosting
- A phenomenon where pressing several keys at once causes some of them to be missed, or a key that was never pressed to be reported as pressed, due to the physical limits of the keyboard's internal wiring.
- Key matrix
- The grid-shaped internal wiring that lets a keyboard detect many keys using relatively few wires. Cheaper keyboards tend to have stricter matrix limits, making them more prone to ghosting.
- Anti-ghosting
- Design measures, such as adding a diode to each key, that reduce or eliminate ghosting. It is one of the main features advertised on gaming keyboards.
- ANSI layout (US layout)
- A keyboard layout with a wide rectangular Enter key and symbol placement following US English conventions. It is the standard in most countries outside Japan.
- JIS layout
- The keyboard layout defined by Japanese Industrial Standard JIS X 6002, with a tall L-shaped Enter key and extra keys such as Zenkaku/Hankaku, Henkan, Muhenkan, and Kana for Japanese text input.
- Chattering
- A fault where worn physical contacts inside a key cause a single press to register as multiple inputs, or stop registering at all. It becomes more common as a keyboard ages.
- KeyboardEvent.code
- A browser-provided identifier for the physical position of the key that was pressed. Unlike the printed character (key), it always refers to the same physical position regardless of keyboard layout or OS language settings.
Frequently asked questions
Side Note — how a jamming problem on typewriters gave us the QWERTY layout
The QWERTY layout used on nearly every modern keyboard was not designed with computers in mind at all. It traces back to the practical typewriters built by Christopher Sholes and his collaborators in the late 19th century. Those machines used mechanical type bars that swung up to strike the paper, and placing frequently paired letters on adjacent keys made the bars collide and jam in mid-air.
To reduce these jams, Sholes deliberately spread out letters that commonly appear together in English — an arrangement that looks inefficient at first glance but was, in fact, a clever workaround for a mechanical constraint. That layout is the direct ancestor of the QWERTY keyboards we still use today. Ironically, a design born to solve a mechanical jamming problem has survived as the keyboard standard well into the electronic era.
The "ghosting" this tool checks for has a completely different cause than the physical jamming of typewriter bars. Modern keyboards use a wiring scheme called a key matrix to detect many keys with relatively few wires, scanning rows and columns electrically. Because of how this wiring works, pressing three specific keys at once can send an electrical signal down an unintended path, causing a fourth key you never touched to register as pressed, or causing one of the keys you actually pressed to go undetected. In a sense, the physical jamming of the past has been replaced by an electrical one.
Features like "anti-ghosting" and "NKRO support" on gaming keyboards exist specifically to prevent this kind of electrical interference, often by adding a diode to every single key. The problem that plagued typewriter engineers more than a century ago — "things jam when you move them together" — has simply changed shape and been handed down to today's keyboard designers.