Keyboard, gamepad, mouse, touch screen: every key and button.
Press each key: it lights up while held and stays marked once tested, so a dead key stands out. Below the drawing, the last key in detail (key, code, side) and any key not drawn (numpad, F13…). While the tab is open, keys do nothing else (Tab, F5, Space…), except with ⌘ or Ctrl. Esc is tested on the first press; press it again to go back.
Layout: the software layout (AZERTY, QWERTZ, QWERTY, Dvorak, Colemak) comes from the system in Chrome and Edge, otherwise from the keys you type. No browser tells the hardware layout: it’s assumed from the software layout and your language, and detected for sure when you press a key that only exists on it (the < > key next to left Shift on ISO; ¥ or kana keys on JIS). The drawing follows (ISO: L-shaped Enter, short left Shift; ANSI: wide Enter, long left Shift), or pick ISO or ANSI yourself. The bottom row follows the system (Mac or PC).
Some keys never reach a web page (Fn, Print Screen on some systems, media keys): that’s normal, not a fault.
Mouse: each button lights up; two presses of the same button less than 80 ms apart are a suspect double (a worn switch: a real double-click takes more than 100 ms). The rate while moving is the mouse’s own rate in Chrome; elsewhere it is limited to the screen. Touch: each finger leaves a trail, to see whether the whole screen responds, and how many fingers it reads at once. On the keyboard, held together shows how many keys the keyboard reads at once, and a bounce is a key that types twice.
Plug in or pair a gamepad, then press a button: browsers only show a gamepad after that, for privacy. Buttons light up, triggers fill in, sticks move. On the right, every button and axis. At rest, a stick should stay close to 0: a value that stays beyond about ±0.10 is drift (most games ignore a small dead zone). Vibrate works when the gamepad and the browser allow it (Chrome, Edge).
Free, no account, nothing is sent: it runs in your browser, even offline.