What a full size board has that the others do not
A full size keyboard is the 104-key ANSI layout: the alphanumeric block, a function row across the top, the navigation cluster with Insert, Home, Page Up and the arrow keys, and a 17-key number pad on the right. It is the layout most desktop keyboards ship with and the one most office machines have on the desk.
The extra keys are exactly the ones people forget to test. A keyboard can feel completely fine for a week of typing and still have a dead Numpad 5 or a Page Down that does nothing, because ordinary typing never touches them. That is why this test marks every key it has seen and leaves the rest untested rather than assuming silence means working.
Test the number pad separately
Num Lock decides what the number pad sends. With Num Lock on, Numpad 4 sends the digit 4. With it off, the same physical key sends a left arrow, and some keyboards then report it under a different code entirely. If the pad appears dead, press Num Lock once and try again before concluding anything is broken.
The number pad is also the part of a keyboard most likely to be switched off in firmware on a laptop with a compact layout, where the pad is overlaid on the letter keys and only wakes with Fn.
The keys that will not report, and why that is normal
Print Screen is often intercepted by the operating system or a screenshot utility before the browser sees it. The Windows and Command keys frequently open a system menu instead of reaching the page. Those caps are drawn with a dashed outline here and are never counted as failures, because a browser cannot prove they work.
Everything else on a full size board is fair game, and a board where all 100 reportable keys report in is a board with no dead switches.
What to do with the result
- One key dead, everything else fine: the switch or its solder joint, not the keyboard. On a hot-swap board, swap the switch. On a soldered board or a laptop, it is a repair.
- A whole row or column dead: a matrix fault or a ribbon cable, which on a laptop is usually the connector rather than the keys.
- Nothing reports at all: driver, cable or port before anything else. Try another port and another machine.
- Keys firing twice: switch chatter rather than a dead key, which has its own page.