How to use it
- Press Start webcam test and allow camera access. Your picture appears mirrored, as in most video-call apps; untick Mirror to see it the way others do.
- Check the numbers under the picture: the resolution the camera is actually sending, the frames per second, and a brightness reading with a plain-language note if the picture is too dark or has blown-out white areas.
- Ask for a higher resolution from the list to see what your camera can really do, pick another camera if you have more than one, and take a snapshot at full resolution.
What the numbers mean
Resolution. A web page can only ask a camera for a resolution; the browser then picks the closest mode the camera supports. The size shown is what really arrives, read from the video itself, and the page tells you when it differs from what you asked for. When a page asks for no size at all, the browser picks one: Chrome’s test camera came up at 640×480 in our tests even though it can do 4K, so a camera can be capable of more than an app shows.
Frames per second is counted from the frames that actually reach the page over the last two seconds, not taken from the camera’s own claim, which is also listed under “What the browser reports”. If the counted rate is well below the reported one, frames are being lost on the way to the page; closing other camera apps and heavy tabs is the first thing to try.
Brightness is the average luma of a small sample of each frame on a 0 to 255 scale (using the Rec. 709 weights for red, green and blue), plus the share of pixels that are nearly black or nearly pure white. Very dark usually means too little light or a closed privacy shutter; a lot of pure white usually means a bright window or lamp behind you.
If it does not work
- Access blocked: allow the camera from the icon in the address bar or the site settings. On a Mac, the browser also needs permission in System Settings › Privacy & Security › Camera; on Windows, in Settings › Privacy & security › Camera.
- Camera busy: only one app may be able to use the camera at a time on some systems. Close calls, other tabs and camera apps, then try again.
- Black picture: check for a physical shutter or a camera key on the keyboard, and pick the right camera if you have several.
What we tested
On October 15, 2026, in Chromium with its built-in test camera: by default it delivered 640×480 and the page counted 20.0 frames per second against the 20 the track reports; asking for 640×480, 720p, 1080p and 4K delivered exactly those sizes (the test camera supports them all, up to 3840×2160), the counted frame rate matched each time, and every snapshot PNG had the same pixel size as the video. With the camera limited to 720p, choosing 4K showed: “You asked for 3840×2160; the camera delivers 1280×720, the closest it supports.”. The brightness maths gave 128 for a flat mid-grey frame, 182.4 for pure green and half dark, half bright for a black-and-white frame; a blocked permission showed the instructions above; the page fits a 390 px screen.
Sources
- W3C, Media Capture and Streams (camera access and how requested sizes are matched to what a camera supports).
- MDN, the requestVideoFrameCallback() method of video elements (counting frames as they are presented).
Frequently Asked Questions
Built by Derek Giordano · Part of Ultimate Design Tools