Hardware Tester
Keyboard ghosting & N-key rollover tester
Press any key to light it up. Hold multiple keys at once to measure your keyboard's N-Key Rollover and detect ghosting. Everything runs locally in your browser.
Press any keys— hold multiple keys at once to test your keyboard's N-Key Rollover. Keys light green when held and turn gray when released (tested).
What is N-Key Rollover?
N-Key Rollover (NKRO) determines how many keys your keyboard can register simultaneously. A keyboard with full NKRO can register every key at once — no matter how many you press.
Ghostingoccurs when a keyboard without full NKRO registers key presses you didn't make, or fails to register keys you did press. This happens because cheaper keyboard circuits use a matrix layout that can't distinguish certain 3-key combinations.
Most standard keyboards support 6-key rollover (6KRO) — they can detect up to 6 keys at once. Gaming and mechanical keyboards often advertise full NKRO or 10+ key rollover.
How to test your keyboard for ghosting
- Click the keyboard area above to focus it (your browser needs keyboard focus to detect key presses).
- Press any key — it should light up green. When you release it, it turns gray to show it was tested.
- Hold multiple keys at once— the "Keys Held Now" counter shows how many are currently pressed. The "Max Rollover" counter tracks the highest number of simultaneous keys your keyboard registered.
- Check for ghosting— if a key lights up that you didn't press, or a key you pressed doesn't light up, your keyboard has ghosting.
NKRO vs 6KRO — what's the difference?
6KRO (6-Key Rollover)is the standard for most USB keyboards. The USB HID protocol can report up to 6 simultaneous regular key presses plus modifier keys (Shift, Ctrl, Alt, Win). If you hold 7+ keys, some won't register.
NKRO (N-Key Rollover) means the keyboard can register every key simultaneously — whether you press 6, 10, or all 104 keys. This is common in gaming keyboards and mechanical keyboards that use a separate diode for each switch.
For everyday typing, 6KRO is more than enough. But for gaming (holding WASD plus ability keys plus modifiers) and fast typing tests, NKRO ensures no keystrokes are ever lost.
Frequently asked questions
- What is keyboard ghosting?
- Keyboard ghosting occurs when pressing three or more keys at the same time causes the keyboard to register a key press that didn't actually happen, or fails to register a key that was pressed. This happens on keyboards with limited key rollover because the electrical matrix that scans key presses can't distinguish certain combinations.
- What is N-Key Rollover (NKRO)?
- N-Key Rollover (NKRO) is a keyboard feature that allows the keyboard to register every key press simultaneously, no matter how many keys are held down at once. A keyboard with full NKRO can handle all keys at the same time. Most standard keyboards support 6-key rollover (6KRO), meaning they can only register up to 6 simultaneous key presses.
- How do I test my keyboard for ghosting?
- Press and hold multiple keys at the same time using this tool. Each key you press should light up green. If a key lights up that you didn't press, or a key you pressed doesn't light up, that indicates ghosting. Try holding 6+ keys at once — if they all register, your keyboard likely has full NKRO.
- Does this tool install any software on my computer?
- No. This keyboard tester runs entirely in your web browser using JavaScript. It uses the standard Keyboard API (keydown and keyup events) to detect key presses. No software is downloaded, installed, or run outside your browser.
- Why does my keyboard only register 6 keys at once?
- Most non-gaming keyboards use a USB HID protocol that limits them to 6 simultaneous key presses (plus modifier keys like Shift, Ctrl, and Alt). This is called 6KRO. Gaming keyboards and mechanical keyboards with NKRO use a different protocol that can report more simultaneous presses. Some keyboards have a toggle switch or software setting to switch between 6KRO and NKRO modes.
- Which keys are most affected by ghosting?
- Ghosting typically affects keys that share the same row and column in the keyboard's scan matrix. Common ghosting combinations include W+X+S (which can produce a phantom D press), and certain arrow key combinations. The exact combinations depend on your keyboard's internal wiring.