Every time I needed to check whether my microphone actually worked before a call, or whether a key on a used keyboard was dead, I ended up on some sketchy "free online tester" that wanted an account, showed six ad banners, and — the worst part — happily streamed my webcam to a server I knew nothing about.
So I built the thing I actually wanted: TestOnDevice — 118+ device tests that run 100% in the browser. No installs, no account, and nothing you record ever leaves your machine.
Here's what I learned building it.
The core constraint: the network is off-limits
The single rule that shaped the whole project: no device data touches a server. No webcam frames, no audio buffers, no keystrokes, no sensor readings.
