Refresh Rate Test
Measure the refresh rate your browser is actually painting at, and the frame time behind it.
No permissions. Takes about two seconds.
Keep this tab in the foreground for ~2.5 seconds.
This measures how often the browser is painting, which normally equals the display's refresh rate. If a 144 Hz monitor reads 60 here, the usual causes are the OS display setting still at 60 Hz, a cable or port that can't carry the higher rate, a laptop power-saving mode, or the browser capping animation in the background. A slowest frame far above the median means something stuttered during the run -- run it again.
Frequently Asked Questions
My 144 Hz monitor reads 60 Hz here.
The browser paints at whatever rate the operating system is driving the display, so start with the OS display settings -- a new monitor often defaults to 60 Hz until you change it. Other causes: an HDMI cable or port that can't carry 144 Hz at your resolution, laptop battery-saver modes, or a second monitor at 60 Hz that the browser window is partly on.
How is this measured?
The page asks the browser for an animation frame callback repeatedly for about 2.5 seconds and records the time between consecutive frames. The median interval gives the frame time; refresh rate is 1000 divided by that. Results within a few Hz of a standard rate are snapped to it.
Why does it vary between runs?
Anything competing for the main thread -- another tab, an extension, video playing -- can drop frames during the measurement, which shows up as a high "slowest frame". Close other tabs and run it again; a steady display gives the same number every time.