How this test works
Make slow, overlapping passes across the grid, then tap any empty cells directly. Each tracked press or move inside the grid paints the cell at its reported position. The page doesn't join those positions into a continuous trail, so a fast swipe can leave gaps. A filled cell means input reached this page at a point within it, not that every part of that cell was tested. Numbered markers follow the tracked pointers; cancellation or loss of window focus can also remove them.
The browser reports presses, movement, and releases as pointerdown, pointermove, and pointerup events; older browsers use a touch-and-mouse event fallback. Active counts the pointers currently tracked. Max at once is the highest count since you loaded the page or selected Reset grid. Last type is the browser's type label for the most recent press; Last position is the latest processed press or move, measured from the viewport's top-left corner in CSS pixels. Cells painted is the rounded percentage of grid cells that have filled in. Viewport shows the browser content area's dimensions, while Screen uses the screen dimensions reported by the browser. Both use CSS pixels rather than physical panel pixels. Fullscreen distinguishes browser full screen from the viewport-only overlay described below.
This is an input check, not a hardware diagnosis. A touch-sensing fault and a dead pixel are different problems: a screen can display an image in an area where touch doesn't respond. If the image itself looks wrong, try the dead pixel test. This page doesn't read the digitizer's internal state, measure touch pressure or latency, or repair hardware. For a persistent gap, use the retesting steps below before deciding what to do next.
Frequently asked questions
Does an unpainted cell mean the screen is broken?
Not on its own. Sweep over it slowly, then try a direct tap. Clean the glass and dry your hands; remove gloves, and check whether a screen protector is damaged or lifting. If practical, retest without the protector. Restart the device and try the same area in another app. A repeatable unresponsive area is worth asking the device maker or a repair service about, but this grid can't tell you which part needs repair.
What does Max at once tell me?
It is the largest number of pointers this page has tracked together since you loaded it or selected Reset grid. Add fingers one at a time and keep them on the grid. Use only fingers if you want to compare touch input, since mouse and pen pointers also count. The number depends on the input that reaches the page through the device, operating system, and browser; it is not a measured hardware limit. If a marker disappears while your finger is still down, repeat the gesture. Browser cancellation, system gestures, and loss of focus can end tracking too.
Can I test a touch screen with a mouse?
Hold the mouse button to paint. This lets you try the page without a touch screen, but says nothing about finger-touch response. Last type shows the browser's label for the most recent press, not a list of every active input. A pen may use a different sensing system too, so repeat a pen check with your finger if that is the input you're troubleshooting.
Can this test show ghost touches?
Ghost touch is the name for apparent touch input you didn't make. Set the device on a table, select Reset grid, and watch for new paint or markers. Keep your hands and other pointing devices clear. The page can show unexpected input that reaches the grid, but a mark alone doesn't identify its cause. If it keeps happening, dry the screen and repeat with the charger unplugged, then compare with another app. This helps you describe the problem if you need support.
What does the expanded grid cover?
Expand touch grid moves the grid into an overlay and asks the browser for full screen, giving you more room to check near the edges. If the request is unavailable or refused, the overlay fills the viewport instead; browser bars and system-controlled areas can remain out of reach. Fullscreen reports on for browser full screen and overlay for the fallback. Entering or leaving this view clears the painted cells, but keeps Max at once. Tap the grid to show the exit button, or press Esc on a keyboard.
