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…
Modifier Key Test
Tests Shift, Ctrl, Alt, Meta, Caps Lock, Tab and Escape, telling the left and right versions of each apart.
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The test starts automatically — follow the prompts above.
In short
Modifier Key Test is a free online tool on inputtesthub.com that tests Shift, Ctrl, Alt, Meta, Caps Lock, Tab and Escape, telling the left and right versions of each apart. 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 Modifier Key Test
- 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 Modifier Key Test
The Modifier Key Test tests Shift, Ctrl, Alt, Meta, Caps Lock, Tab and Escape, telling the left and right versions of each apart. 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
- Finding out whether it is the left or right Shift that has failed.
- Checking Caps Lock after remapping it to Ctrl.
Left and right modifiers send different codes, which is why a shortcut can work with one hand and not the other. This test shows you exactly which one is arriving.
Explained in our guides
All guidesFrequently asked questions
Why does a key light up in the wrong place?
The test reads the physical key position, not the printed letter, so a non-QWERTY layout will light the key that sits in that position on a US keyboard. That is correct behaviour — it means the test works the same on AZERTY, QWERTZ and Dvorak.
Some keys do nothing at all. Is my keyboard broken?
Not necessarily. Browsers keep a few combinations for themselves — F11, F12, Ctrl+W, Ctrl+T, Cmd+Q, Alt+Tab and the Windows key among them — and act on those instead of passing them to the page. Media keys, Fn-layer keys and macro keys usually never reach the browser either.
Is anything I type recorded?
No. The test runs entirely in your browser tab, keeps only which keys were pressed, and forgets even that when you close or reload the page. Nothing is sent to a server.
Do I need an account to use the Modifier Key Test?
There is no cost and no cap. The Modifier Key Test is not a demo of a paid product, so nothing is held back or watermarked.
Does anything I enter leave my computer?
No. The Modifier Key Test runs entirely in your browser using JavaScript. Because the work happens locally, the page also keeps working if your connection drops, and closing the tab is all it takes to discard everything.
What problem does the Modifier Key Test solve?
Typical uses: finding out whether it is the left or right Shift that has failed. Checking Caps Lock after remapping it to Ctrl. It is built for exactly those cases rather than being a general-purpose tool with this bolted on.
What do people usually get wrong here?
Left and right modifiers send different codes, which is why a shortcut can work with one hand and not the other. This test shows you exactly which one is arriving.
Why does the test start on its own?
No installation, no extension and no driver. The Modifier Key Test 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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