Frame Skipping Test
This frame skipping test lights up one grid cell per screen refresh, synced to your browser's real
render cycle via requestAnimationFrame — not a timer, so it tracks your display's
actual v-sync. Photograph the moving block with a slow camera shutter and the resulting streak of
light shows you, directly, whether every refresh your monitor is supposed to draw actually made it
to the panel.
How to Run the Frame Skipping Test
- Tap Start test. The page goes fullscreen (where your browser supports it) and the grid takes over the whole screen.
- Open your phone's camera app and switch to Pro or Manual mode, then set the shutter speed to around 1/10s. Most stock camera apps hide this behind a "Pro" toggle; third-party manual-camera apps expose it directly.
- Hold the camera steady, fill the frame with the display, and take the photo. A tripod or resting the phone against something steady removes hand-shake as a variable.
- Tap anywhere on the grid to exit the test when you're done.
How to Read Your Photo (Trail vs. Gaps)
Because the block advances exactly one cell per render, a long exposure captures it as a continuous streak — a short line of lit cells with no dark break in the middle. An unbroken trail means your monitor displayed every frame the browser rendered. A dark gap in the middle of the trail — a cell that should be lit but isn't — means a frame was skipped between two exposures.
How many cells you should expect to see lit in one exposure depends on your shutter speed and your monitor's refresh rate:
| Refresh rate | Cells lit at 1/10s exposure |
|---|---|
| 60 Hz | 6 |
| 90 Hz | 9 |
| 120 Hz | 12 |
| 144 Hz | ~14 |
| 165 Hz | ~17 |
| 240 Hz | 24 |
If your photo shows noticeably fewer lit cells than the table predicts for your refresh rate — and the gaps are irregular rather than evenly spaced — that's a real dropped-frame signature, not just camera timing noise.
Why Monitors Skip Frames
Whatever a monitor frame skipping test turns up, the mechanism is usually the same: something in the chain between your GPU and the panel misses a beat. The usual suspects: a cable or adapter that can't sustain the bandwidth your resolution and refresh rate need, a GPU driver that mis-paces frame delivery, a laptop throttling its GPU to save battery, a USB-C dock adding timing jitter, or a monitor picture mode (motion interpolation, overdrive) that reprocesses each frame instead of showing it directly. Background CPU load — screen recorders, antivirus scans, too many browser tabs — can also delay a frame past its refresh window.
Adjusting the Grid for Your Camera and Screen
Tap the gear icon in the corner of the test (or the Grid settings button on this page) to open the settings sheet:
- Grid columns / rows — more cells make each lit block smaller and the trail finer-grained, which is useful on a high-resolution photo taken up close. Fewer cells make the block bigger and easier to photograph from a distance or on a lower-resolution camera.
- Block color — bright green is the default because most camera sensors resolve it cleanly against black without clipping to white the way pure red or blue can. If your photos come out overexposed on the lit cell, try a dimmer or different color.
Frame Skipping Test FAQ
Why is my monitor dropping frames?
The most common causes are a GPU that can't render fast enough to keep up with your refresh rate, a cable or adapter that can't carry the full bandwidth for your resolution and refresh rate combination, or a compositor/OS scheduling hiccup that misses a vertical sync window. Background CPU load (recording software, browser tabs, antivirus scans) can also push a frame late enough that the display shows the previous one twice.
Why is my monitor skipping frames?
"Skipping" and "dropping" describe the same symptom: a frame that should have appeared on screen doesn't, so the previous frame holds for an extra refresh. It shows up as micro-stutter even when your reported FPS counter looks fine, because an FPS counter counts frames rendered, not frames actually displayed without a repeat.
What causes frame skipping?
Frame skipping happens whenever the chain from GPU to panel misses a beat: a dropped or corrupted signal over a marginal HDMI/DisplayPort cable, a laptop silently throttling the GPU to save power, a USB-C dock or hub adding timing jitter, driver-level frame pacing bugs, or the display itself being set to an interpolation or overdrive mode that reprocesses frames instead of showing them directly.
How do I fix frame skipping?
Try a known-good cable rated for your resolution and refresh rate first — it's the most common fix. Then update your GPU driver, set the monitor's picture mode to its lowest-latency/direct mode (turn off motion interpolation), plug directly into a GPU port instead of through a hub, and disable any OS-level display scaling or mixed-refresh-rate setup that can force a compositor to recomposite frames.
How do I check my monitor's refresh rate?
On Windows, go to Settings → System → Display → Advanced display, and read the "Refresh rate" field for your monitor. On macOS, open System Settings → Displays → Advanced and check the Refresh Rate dropdown. Either one works as a quick monitor frame rate test and tells you what the OS is driving the panel at — this frame skipping test then tells you whether every one of those refreshes is actually reaching the screen.
Why does my monitor stutter?
Stutter is what dropped or skipped frames feel like in motion — a brief hitch even though your average frame rate looks smooth. It's caused by inconsistent frame timing rather than a low frame rate itself, which is why a game can report 100+ FPS and still feel stuttery: a handful of late or repeated frames per second is enough to be visible.
