ReactionMetric.

ReactionMetric measures how fast you respond to a signal, and spends as much effort explaining the number as producing it. In the main test you wait for the panel to turn green and click, tap or press Space, five valid times, with early clicks discarded. Your score is the median of those five, shown alongside your best, worst and a consistency measure, so one lucky click doesn't define the result. The site gives rough reference points, about 250 ms as common in simple visual browser tests and around 200 ms as fast, and says plainly that your display, input device and system all add delay. Percentiles appear only when a comparison group with a similar setup has at least 100 contributed sessions. Other tests cover sound, keyboard, F1-style light starts, clicks per second and double-click diagnostics. No account is needed, history stays in your browser, and trial values are uploaded only if you opt into the anonymous benchmark. The site describes these as browser-observed performance tools, not medical diagnostics.

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