F-Key & Modifier Tester
Test F1 to F12 and the modifiers — and see which keys a browser can never receive.
Click the pad first so it has keyboard focus. Dashed keys are ones the system usually takes.
How this test works
Each function and modifier key is drawn and lights when it registers, matched on physical key position. The value here is mostly in what the page admits it cannot do. The Fn key is the clearest case: it is handled entirely inside the keyboard's own controller, which turns Fn plus F3 into a brightness command before the operating system is involved, so Fn itself has no key code and no browser will ever report it. F11 and F12 are claimed by the browser for fullscreen and developer tools. On many laptops the whole function row defaults to media controls, so a plain press sends volume rather than F5. All of those are marked reserved and excluded from the failure count, because a tester that scores them as broken keys is how people end up replacing a keyboard that works.
What the results mean
- Function keys tested
- Distinct positions in the F row and the modifiers that registered a press.
- Reserved by the system
- F11, F12 and similar. Taken by the browser before the page sees them — not faults.
- Stuck keys
- A press with no release. A real fault, and the only one this page asserts.
- Fn
- Absent by design. It never becomes an event, so it cannot appear here at all.
Common problems and fixes
- F11 and F12 do nothing on this page
- They are doing something — fullscreen and developer tools respectively. The browser takes them first, which is why they are drawn as reserved.
- Pressing F5 changes my volume instead
- The laptop's function row is in media mode. Hold Fn to send the F-key, or switch the default in the firmware settings, usually called Function Key Behaviour or Fn Lock.
- The Fn key never lights up
- It never will, on any site. Fn is resolved inside the keyboard controller and produces no event for a browser to receive.
Frequently asked questions
Why can no website test the Fn key?
Because it is not a key in the sense the operating system understands. The keyboard's own controller interprets Fn plus another key and emits the resulting command, so Fn alone never generates a key code. There is nothing for a browser to receive.
Why do my function keys control brightness instead of acting as F1 to F12?
The laptop's firmware defaults the row to media and hardware controls. Most machines expose a Fn Lock toggle or a firmware setting, often called Function Key Behaviour, to reverse it.
Are untested keys a sign my keyboard is failing?
No, and treating them that way is the main error these tools make. About a dozen keys never reach a web page under normal settings. Only a stuck key — pressed with no release — is a fault this page can see.