MEASUREMENT PROTOCOL

Methodology

ReactionMetric is designed to be transparent about what a browser can and cannot measure.

Short version

Five valid trials. Median is the headline score. Early clicks do not count. Your device and browser add delay, so ReactionMetric shows the timing it observes instead of guessing that delay away.

Protocol

Each session requires five valid trials. After you start, the test waits for a randomized delay. The ready state is committed on an animation frame, then ReactionMetric timestamps the visual-ready event and your response using the same high-resolution monotonic browser clock.

False starts and valid-trial window

If you respond before the signal appears, that round is marked as a false start and excluded. After the signal appears, ReactionMetric accepts browser-observed responses from 100 to 3000 ms. Responses under 100 ms are treated as anticipatory and responses over 3000 ms as lapses; neither counts toward the five valid trials. The 100 ms lower bound follows a common data-cleaning convention in reaction-time research rather than claiming that human physiology has one universal hard cutoff. Examples include a browser-based simple reaction-time study and a visual reaction-time study that excluded responses below 100 ms.

Background tabs

If the page becomes hidden during a waiting or ready phase, the round is invalidated. Browsers throttle background work, so keeping that round would reduce comparability.

What the score means

The displayed milliseconds are browser-observed visual response time. They are not a pure measure of nervous-system latency. Display refresh, input hardware, operating-system scheduling, browser scheduling and system load can all contribute.

No guessed latency correction

ReactionMetric does not apply a fixed subtraction for “browser latency” or claim to know your monitor and mouse hardware delay. Instead, it records coarse environment context and can compare similar setups when enough first-party data exists.

Environment quality

The browser estimates display refresh rate from animation-frame intervals and labels the sampled frame stream as stable or unstable. Where supported, the Long Tasks API is used only as a coarse busy/clear signal for main-thread jank. These are measurement-quality hints, not hardware calibration, and benchmark storage keeps only coarse quality labels rather than detailed device fingerprints.

Benchmark protocol versions

The current public benchmark is task version 2. Version 2 applies the 100–3000 ms valid-trial window and is kept separate from earlier benchmark rows so a protocol change does not silently mix incompatible populations.

Summary statistics

We report mean, median, best, worst and standard deviation. Median is resistant to a single unusually slow trial, while standard deviation helps describe session consistency.