It checks the three things that go wrong at the start of a video call, in three tabs:
- Camera: a live preview with a device picker, and the numbers the browser actually gets from the camera: resolution, aspect ratio, megapixels, the frame rate the camera is set to and the rate measured from the frames that arrive, and the largest size the camera reports. A resolution test asks the camera for 360p, 480p, 720p, 1080p, 1440p and 4K in turn and records what it really delivers. A lighting check reads the frame once a second and says whether it is too dark, washed out, clipped or tinted. You can mirror the preview and save a PNG snapshot.
- Microphone: a level meter in dBFS with a held peak, an estimate of the room's noise floor, how far speech rises above it, and a five-second record and play back so you hear what others will hear.
- Speakers: a short tone on the left, the right or both channels, to check that headphones are the right way round and that sound comes out at all.
How the permission flow works
Nothing starts until you press Start camera or Start microphone; the browser then asks for permission. If you refuse, the tool says so and explains where to allow it (the icon in the address bar, or on macOS and Windows the system privacy settings, which can block a browser even when the site is allowed). If no device is found, or another app is using it, you get that message instead of a black box. Device names appear in the picker only after the first permission, because browsers hide them until then.
The video and sound stay on your device. Nothing is uploaded or recorded unless you press Save snapshot (a PNG made in the page) or the five-second playback (kept in memory and discarded when you leave). Leaving a tab switches its device off.
Reading the camera numbers
The resolution is what the camera is sending now. The tool asks for 1280 × 720 by default, so a camera stuck at 640 × 480 is an older or lower-end device, or another app holds it at that size. The resolution test asks for each size exactly. Where the browser supports it, it asks for the camera's own modes rather than a picture scaled down by the browser, so a 720p row that says "Delivered exactly" means the sensor really outputs that size. A 4K row that says "Refused" is normal for most laptop cameras; video calls rarely send more than 720p or 1080p anyway, whatever the camera can do.
Frame rate shows the rate the camera was set to and the rate measured from frames that actually arrive (in browsers that can report frames). In dim light many webcams lower the frame rate to expose each frame longer, so a camera set to 30 fps may deliver 15: add light and the measured rate rises.
The lighting check shrinks a frame to 96 × 54 pixels and averages it: brightness, the share of pure-white and pure-black pixels, and the average colour. Its thresholds are rules of thumb for a face in front of a camera; a red wall or a blue screen behind you will look like a colour cast to it.
Reading the microphone numbers
Levels are in dBFS, decibels below the loudest value the microphone can record: 0 dBFS is the top, −6 is half the amplitude. For normal speech, peaks between about −20 and −6 dBFS are comfortable; peaks touching 0 dBFS clip and distort. The noise floor is the level of the quiet moments between words (the 10th percentile of recent readings): a quiet room sits around −60 dBFS or lower, a laptop fan or traffic around −45. Speech above noise is the difference between your loudest speech and that floor; 30 dB or more sounds clean. If the floor reads as digital silence, the input is muted or a noise gate is closing it.
The processing switch turns the browser's echo cancellation, noise suppression and automatic gain on or off, as most call apps use them. Compare both: if the raw microphone hums, the suppression is doing a lot of work and the voice may sound watery.
Speakers and headphones
The tones last a second and a half at a moderate level; still, lower the volume first. The left tone must be heard only on the left, the right only on the right. A tone on both sides when you chose one means the output is mono or the headset is set to a mono mode; nothing on one side means a broken cable or driver. The 100 Hz tone checks small laptop speakers, which may barely reproduce it. Before an interview, run the whole check in the same room and with the same headset you will use; testing a webcam and microphone before an interview has a short checklist, and the voice recorder records longer takes.
