Run a repeatable moving-edge comparison
Begin with the middle speed and dark gray background. Start motion if it is paused, then follow the moving rectangle with your eyes rather than staring at one fixed point. Look for a soft trail, a darker smear, or a bright outline around the trailing edge. Keep a short viewing session and pause whenever you want a break. The reduced-motion preference starts the pattern paused, so motion remains a deliberate choice.
Try the light and mid-gray backgrounds next. Different transitions can reveal different behavior; a result on white against gray does not describe every transition in a game. Increase speed gradually while keeping the background and monitor setting fixed. Use fullscreen to remove nearby page movement, and return with Exit or Escape. On a phone, the fallback expanded view may leave browser controls visible. The object wraps around at the edge, so judge the central part of its travel rather than the wrap point.
Separate trails, blur, and cadence
A persistent trail can be associated with pixel transitions, but this visual comparison does not calculate response time in milliseconds. Bright or dark outlines may become more noticeable with a monitor's aggressive overdrive setting. Compare the display's available response-time modes one at a time and note the tradeoff rather than assuming the fastest labeled mode is always best. These labels are manufacturer settings, not browser measurements.
Eye tracking on a sample-and-hold display also produces perceived motion blur even when individual pixels transition quickly. Judder can come from uneven frame delivery or a low selected cadence. The target control caps drawing cadence within the callbacks the browser provides; it cannot create physical refreshes the panel lacks. A 120 fps target on a 60 Hz path still depends on approximately 60 callbacks per second, and targets that do not divide the browser cadence evenly can have uneven frame spacing.
Use the browser timing readout carefully
The readout averages recent requestAnimationFrame callback intervals while this tool is visible. It reports browser delivery, not a certified monitor refresh rate, and it does not count physical scanouts or measure pixel settling. Tabs, operating-system load, power saving, compositor behavior, and the active display can all affect delivery. Motion stops while the page is hidden or the pattern is offscreen; returning resumes the comparison without accumulating a huge time jump.
If motion stutters, close heavy work, check the selected display and refresh rate, and retry the same controls. Compare the refresh-rate tool for a separate browser timing observation and the FPS comparison for a broader cadence demonstration. If a trail appears only under one overdrive mode or background, record those conditions. Screenshots freeze a rendered image and cannot preserve the panel's temporal behavior. A camera recording introduces its own exposure and sampling, so it is supporting context rather than a response-time measurement.
Example: an overdrive halo versus uneven movement
Suppose a bright fringe appears behind the rectangle only after you select a stronger monitor overdrive mode. Keep the background, speed, and target cadence unchanged and return to the previous mode. If the fringe becomes less visible again, document that tradeoff rather than choosing the fastest label automatically. A distinct bright or dark halo can be an overdrive artifact; this visual check does not quantify overshoot or response time.
Uneven movement is a separate comparison. If the rectangle jumps irregularly without gaining a fringe, hold overdrive fixed and compare the available cadence targets. Browser scheduling and a target that does not divide the delivered callback cadence evenly can affect the spacing of updates. A smoother target does not prove faster pixel transitions. Record the selected target and browser timing readout separately from any trail you see on the physical display.
Frequently asked questions
Does this test measure monitor response time?
No. It renders a moving edge for subjective comparison. Browser timestamps cannot observe physical pixel transitions, so the page does not output a response-time score or a pass/fail verdict.
Why is a 144 fps target not always smooth?
The browser draws only when callbacks arrive. A target that does not divide the available cadence evenly may produce unequal spacing, and a lower-rate display cannot show all requested updates.
What does the callback number mean?
It is a recent average of browser animation callbacks while the pattern is visible. It may differ from physical refresh rate and should be read alongside your operating-system display settings.
Why did motion start paused?
Your system may request reduced motion. The tool respects that preference by starting paused; press Start motion when you choose to inspect the moving pattern.
Should I use maximum overdrive?
Compare available modes at the same speed and background. Strong overdrive may reduce one trail while adding bright or dark overshoot. Choose based on your normal content and display guidance.