Guide
Why a USB Keyboard Stops at Six Keys
A USB keyboard's basic report has room for six keys plus modifiers, so a seventh key vanishes. How 6KRO and…
Key Rollover Test (NKRO)
Measures how many keys your keyboard can register at once. Membrane boards usually stop at six; n-key rollover boards keep going.
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In short
Key Rollover Test (NKRO) is a free online tool on inputtesthub.com that measures how many keys your keyboard can register at once. Membrane boards usually stop at six; n-key rollover boards keep going. It needs no account, no download and no payment, and there is no daily usage limit. Everything is processed inside your own browser, so the data you paste is never uploaded to a server.
How to use the Key Rollover Test (NKRO)
- The test starts on its own — no button to press and nothing to install.
- Follow the prompt in the test panel and watch the readings update live.
- Press Reset to start over with a clean slate.
About the Key Rollover Test (NKRO)
The Key Rollover Test (NKRO) measures how many keys your keyboard can register at once. Membrane boards usually stop at six; n-key rollover boards keep going. It runs as plain JavaScript inside the page, which means there is no upload step, no queue and no size limit imposed by a server — the only limit is your own device.
What people use it for
- Checking whether a keyboard really has the n-key rollover its box claims.
- Working out why a game misses inputs when you hold several keys.
Details
| Typical membrane board | 2 to 6 keys |
|---|---|
| USB boot protocol limit | 6 keys plus modifiers |
| True NKRO | every key at once |
Hold keys down with as many fingers as you can and watch the "most at once" figure. Modifiers such as Shift and Ctrl are handled separately in the USB protocol and usually do not count against the limit.
Explained in our guides
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How to Test a Keyboard Properly
A key that seems dead is usually not a broken switch. Test in the right order — registration, rollover…
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Why a Key Does Not Register
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Frequently asked questions
I can only get six keys. Is my keyboard bad?
Six plus modifiers is the limit of the USB boot protocol, which many keyboards use by default for BIOS compatibility. Some boards have a key combination or a switch to enable full NKRO — check the manual. Others genuinely cap at six.
Why do some combinations fail earlier than others?
That is ghosting rather than rollover. Cheap keyboards share wires across a matrix, so certain three-key combinations become ambiguous and the keyboard drops one. Which combinations fail depends on the matrix layout.
Does the browser limit this?
The browser reports every key it receives, so the ceiling you find here is the keyboard's and the USB protocol's, not the browser's.
Does the Key Rollover Test (NKRO) cost anything?
No charge and no sign-up. There is no free tier to run out of because there is no paid tier — inputtesthub.com is funded by advertising rather than by metering the tool.
Is what I paste into the Key Rollover Test (NKRO) stored?
No. The Key Rollover Test (NKRO) runs entirely in your browser using JavaScript. Nothing is transmitted, logged or stored, which you can verify yourself in the Network tab of your browser's developer tools.
What do people use the Key Rollover Test (NKRO) for most?
In practice it gets used for three things: checking whether a keyboard really has the n-key rollover its box claims. Working out why a game misses inputs when you hold several keys. It is built for exactly those cases rather than being a general-purpose tool with this bolted on.
Is there anything to watch out for?
Hold keys down with as many fingers as you can and watch the "most at once" figure. Modifiers such as Shift and Ctrl are handled separately in the USB protocol and usually do not count against the limit.
Which values should I know?
Typical membrane board is 2 to 6 keys. USB boot protocol limit is 6 keys plus modifiers. True NKRO is every key at once. These are printed on the page itself, so you do not have to take them on trust.
Does the Key Rollover Test (NKRO) need an app or a driver?
No installation, no extension and no driver. The Key Rollover Test (NKRO) uses the browser's own device APIs and begins as soon as the page loads, so there is nothing to press first. Press Reset at any point to start over with a clean slate.
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