Input Diagnostic
Keyboard Test
Verify every key on your keyboard, detect dead keys, and test your N-Key Rollover (KRO) capacity in real-time.
Interactive Matrix Tester
⚠️ OS Limitations: The "Fn" key and certain system-level shortcuts (like Windows Key + L or Mac Command + Q) are intercepted by your Operating System and cannot be detected by any web browser.
Understanding Keyboard Ghosting and KRO
When gaming or typing exceptionally fast, you may press multiple keys simultaneously. A cheap or poorly designed keyboard matrix might fail to register some of these keys, or worse, register a key you never pressed. This phenomenon is known as Keyboard Ghosting.
N-Key Rollover (KRO) defines the maximum number of keys your keyboard can register at the exact same time. Standard office keyboards typically feature 2-Key or 3-Key Rollover (2KRO / 3KRO), meaning pressing 4 keys at once will result in dropped inputs. High-end mechanical gaming keyboards feature NKRO (N-Key Rollover), allowing you to press every single key on the board simultaneously without losing a single input.
This diagnostic tool captures the raw keydown and keyup events directly from your browser engine. It maps the physical scancodes (e.g., KeyW, Space) rather than localized layouts, ensuring accuracy across QWERTY, AZERTY, and custom keyboard setups.
FAQ & Limitations
Why is the "Fn" (Function) key not lighting up?
The "Fn" key is a hardware-level modifier. It does not send a scancode to the operating system or the browser. It only alters the signal of other keys internally within the keyboard's own microcontroller.
Why did my screen capture tool or start menu open?
Certain keys like the Windows Key, Print Screen, or system-level combinations (Ctrl+Alt+Del) are intercepted by the operating system before the browser can stop them. They will usually register in the tool, but they may also trigger their system function.