Reaction Time Test

1. Click Start to show the red waiting box.
2. A setTimeout schedules a callback after a random delay of 1.5–4 seconds. The callback records performance.now() and requests the green ready state.
3. Activating the box while waiting produces a false start and no score.
4. In the ready state, a click or Enter/Space activation records another performance.now(). The difference is rounded to whole milliseconds.
5. The result shows your score, a title, and your local personal best when browser storage is available. You can screenshot the result card or share the test link.

The timestamp starts before the browser paints the green pixels. This test does not measure the actual moment light reaches your eyes or isolate your nervous system's response.

Results mix your response with display, operating-system, browser, and input delays. Keep the same device, browser, and input hardware when comparing attempts. No fixed latency correction is applied, and no independent accuracy measurement is claimed.

Scores and title thresholds are for entertainment, not medical or laboratory assessment. Titles are site-defined bands, not population percentiles, professional qualifications, or world records.

Your personal best is stored in this browser's local storage when available. It does not sync across browsers or devices and can disappear if site storage is cleared. The site also loads Google Analytics 4, Microsoft Clarity, and Cloudflare Web Analytics; local score storage does not mean the whole site makes no third-party requests. See the Privacy link beside the test.