Key Rollover & Ghosting Tester
Test how many keys your keyboard reports at once, and see which combinations reach the browser.
What is Rollover Tester?
Rollover is how many keys a keyboard can report at the same time, and ghosting is what happens when it cannot: a missing diode in the matrix makes a board report a key nobody pressed, or drop one that was. It matters most in games and for anyone typing chords quickly. This is the test for it, with the caveat that makes it worth trusting: three layers can eat a keystroke before the page sees it, and the page says which.
How it works
Every keydown adds a key to the held set and every keyup removes one, keyed by physical key code rather than by character so the result does not depend on the layout. The page tracks the largest number of simultaneous keys seen, which is the practical measure of what the board reports, and logs each new combination with how often it was seen. Key repeats are ignored — counting them would make every keyboard look unlimited — and keys released while the window is unfocused are cleared rather than left held, because a keyup can be missed entirely.
- Enter your input. Type or paste your input into the field above — the tool responds instantly.
- Review the result. Output updates live as you type. Everything runs entirely in your browser.
- Copy or download. Use the Copy button to grab the result, or Download to save it as a file.
Examples
Realistic sample
Type or paste any realistic input — the tool computes the result locally and instantly.
Common mistakes
Expecting a server round-trip
Nothing is uploaded — every tool in this category runs entirely in your browser.