How Browser-Based Reaction Time Tests Measure Your Speed

A browser reaction test asks users to click once a color changes, timing the gap between the signal and the response. Such tests rely on a random delay before the signal, so the moment cannot be predicted, and clicks made before the signal count as false starts. The timing uses a high-resolution monotonic clock, but browser rendering, display refresh rates, input handling and main-thread work can all add delay beyond what the timer captures. The article recommends averaging several rounds, allowing retries, and comparing results only on the same device, browser and input method. It also cautions against treating browser results as clinical measurements or as precise cross-hardware comparisons.