How to test touch coverage
Open this page on the phone, tablet or touch laptop you want to check. Wipe away moisture and dirt, then place one finger inside the grid and sweep slowly across each row and column. Cells count as covered only when the browser sends an event whose Pointer Events type is touch. The colored trail shows the path that arrived at the page, while the percentage summarizes how many grid cells received at least one touch. Use several deliberate passes around the edges and corners instead of racing through once.
Next, place two or more fingers down at the same time. Each active touch receives a numbered marker and its own trail color. Fingers now is the current number of browser-reported touch pointers, and Peak at once remembers the largest simultaneous count since Clear. Lift every finger before starting another attempt. If a line repeatedly breaks at the same location or a region remains uncovered after slow, careful passes, repeat the test after cleaning the surface and removing an interfering case or protector if the device maker says that is safe.
Touch, mouse and pen are kept separate
This page uses standard Pointer Events and reads each event’s pointerType. Only pointerType “touch” paints coverage cells and changes the finger counters. A mouse drag is drawn in gray as a desktop preview so you can confirm that the page is interactive, but it is explicitly labelled Mouse and cannot produce a touchscreen pass. A pen is also labelled separately because stylus response does not prove that finger sensing works. Browser capability information such as navigator.maxTouchPoints is shown only as a hint; the page trusts the input type of events actually delivered during this session.
Some operating systems convert certain gestures into scrolling, navigation or mouse-like input before a web page receives them. The browser may also reserve its toolbar, the home indicator, system edges or a gesture area. Those regions cannot be certified by a test running inside one tab. Fullscreen can expose more of the page, but it cannot take control of protected operating-system areas.
How to read the grid and trails
A continuous trail means the page received a sequence of pointer positions along that path. It does not measure the physical accuracy of every sensor electrode, and a coarse browser sampling rate can make a fast stroke look less smooth. Grid coverage means at least one touch event arrived in a cell; it does not automatically declare that cell healthy. Compare slow and moderate strokes, repeat a suspicious path in both directions, and try normal device orientation as well as the orientation in which the problem occurs.
For example, if a keyboard key near the lower-right corner sometimes misses, sweep a finger slowly across that corner several times. If the trail breaks at the same place while neighboring cells fill, note the location and repeat after restarting the browser. As a second example, place three fingers down and move them independently. If Peak at once reaches three, the browser reported three simultaneous contacts during that attempt; it does not promise the device supports the same count in every app or gesture.
Troubleshooting and limitations
Use Clear between controlled attempts so old trails do not hide a new dropout. If the page reports no touch capability on a non-touch computer, that is expected: a mouse can preview the drawing surface but cannot test a digitizer. If a touch device sends no touch events, check whether the browser or operating system is intercepting the gesture, then try the device maker’s supported diagnostics. Avoid pressing hard; this tool needs ordinary touch only. Do not use a browser observation as a reason to open or repair hardware yourself.
This tool does not diagnose ghost touches automatically, measure pressure or latency, calibrate coordinates, repair the digitizer, or inspect touch outside the browser. It records no server-side result and gives no pass/fail badge because missed events have no coordinates for the page to observe. A visible gap is a clue to repeat, not proof of hardware failure. Cases, moisture, charging accessories, software, browser behavior and screen protectors can affect what you observe.
Frequently asked questions
Why does the mouse draw but not increase coverage? The gray mouse preview confirms the canvas and pointer-event path, while keeping mouse input out of touch conclusions. Can I test every edge? Fullscreen may increase the available area, but browser and operating-system gesture regions remain outside the page’s authority. What does Peak at once mean? It is the most simultaneous touch pointers the browser delivered since Clear, not a manufacturer specification. Why can a dead zone stay white? A page cannot receive an event from a location that did not register, so an unpainted region is something to repeat carefully rather than an automatic verdict. Is anything uploaded? No; trails, counters and coverage exist in this page and reset when you choose Clear or leave. What should I do with a consistent problem? Record the conditions in your own words and consult the device maker’s support guidance or a qualified repair service.
Need to inspect the display image instead?
This test checks input delivered to the page, not pixel color or marks. Open the screen test.