Touch Screen Test
A green cell got a touch or pointer event on a CSS-pixel grid. Grey means that cell was not crossed, not that it is a dead zone. Draw sample lines, log extra events, and count points the browser delivers at once.
Touch grid test
Drag slowly over the whole screen, edges and corners included. A cell turns green only when a touch or pointer event lands in it. The grid is CSS pixels, not the panel's physical pixels. A grey cell you never crossed is not a dead zone. A mouse works too, but it tests the pointer, not the touch layer.
Browsers on iPhone do not allow true full screen, so there the grid fills the browser window. Turn the phone sideways or scroll first to shrink the toolbars, and test the strip behind them separately.
More touch tests
Draw slowly along the guides. The line is built from points the browser delivered. A gap means those samples were far apart in CSS pixels. That can be a fast stroke, dropped samples, or a spot that reported nothing. It is not proof the digitiser is broken.
Biggest jump is the largest gap between two samples in one stroke, in CSS pixels, not device pixels. A fast flick spreads samples further apart. A large gap is not, by itself, a broken digitiser.
Reading the results
What green, grey and the log mean
A green cell received a touch or pointer event. A grey cell did not. If you did not drag across a grey cell, it is not a dead zone. A line gap is a stretch where samples were far apart in CSS pixels. The ghost log lists events the page saw during the hands-off window. A palm, moisture, a charger, or a finger can look the same, and this page cannot tell them apart.
Checking a used phone or tablet
"Screen works perfectly" costs a seller nothing to say. Open this page on the device. Run the fine grid in both orientations and drag slowly so each cell can receive a point. Draw lines along the edges, where replacement screens often miss. Then run the 15 second monitor on a table, once on battery and once plugged in, without touching the glass. Events in that log are what the page saw, not a verdict. For the panel image, use the dead pixel test and, on OLED phones, the burn-in test.
Things to try before a repair
Remove the protector and case, clean and dry the glass, unplug the charger, and reboot. On Android, safe mode can show whether an app is involved. Most phones have no touch recalibration control, and calibration apps do not change the digitiser. If the same cells stay grey after slow passes on a bare, dry screen, or the monitor keeps logging events with nothing on the glass, a repair shop can look at the hardware. This page cannot prove the digitiser is broken, and a green grid cannot say there are no dead zones.
Related tools
- Dead Pixel Test: find dead, stuck and hot pixels on the same screen.
- Burn-In Test: spot image retention on OLED phones and tablets.
- Screen Resolution Test: CSS pixels, device pixel ratio, and the viewport the browser reports.
- Gamepad Tester: test controller buttons, triggers and stick drift.
Frequently asked questions
What does a green cell mean?
A green cell received at least one touch or pointer event. Coalesced samples the browser grouped into one move count too. The grid is CSS pixels, not the panel's physical pixels. A full green grid means every cell got a point. It does not mean the digitiser has no dead zones.
Does a grey cell mean a dead zone?
No. Grey means no event landed in that cell. A cell you never crossed is not a dead zone. A fast swipe can skip cells, so drag slowly and pass over grey cells again. If a cell stays grey when you are sure a finger went through it, the browser still got no point there. That is a clue, not proof the digitiser is broken.
What does the ghost monitor record?
Pointer events this page saw during a hands-off window. They are not a proven hardware fault. A finger, a palm, moisture, or a charger can all produce the same event, and the page cannot tell them apart. The table lists time, event type, and position as a share of the window.
What does the multi-touch count measure?
How many points the browser delivered to the pad at the same time. Max at once is that session record, not the panel's rated count. Browser reports is navigator.maxTouchPoints, which can differ from the digitiser. System gestures can cancel fingers before this page sees them.
How do I leave the full-screen grid?
Tap the X. It stays visible and tappable, including after every cell turns green. Esc leaves too. Closing the test or leaving the page exits full screen and removes the listeners. iPhone browsers often block full screen, so the grid covers the window instead, and the X still closes it.
Why can a drawn line have a gap?
The line joins samples the browser delivered. The biggest jump is the largest gap in that stroke, measured in CSS pixels, not device pixels. A fast flick spreads samples out. A gap that returns in the same place on a slow line is worth another pass. It does not, by itself, mean a broken digitiser.
Can I use a mouse for this test?
Yes. A mouse or trackpad sends pointer events, so cells turn green the same way. That checks this page, not a touch digitiser. Use a finger on the phone or tablet you want to check.