What is input lag?
Input lag can refer to different intervals. Physical actuation, a device report, a browser event, an animation callback and visible light have different endpoints. Name them before comparing numbers.
The browser tools start after an event reaches the page. They cannot see the first physical actuation or panel light output. The mouse latency test and keyboard latency test answer a narrower question than an external camera or photodiode test.
What are you comparing: two browser settings, a device specification or a game response? Use the same method in both runs. Network input delay in an online game follows another route and cannot be isolated by this local browser timing.
How to run an input lag test
For mouse input, click the target when it appears and allow the two-animation-frame sample to finish before another press. The tool records from event timestamp to second callback; it does not directly observe visible light.
For keyboard input, press A once per ready sample and release it. Other codes and automatic repeats are excluded. Twenty accepted samples complete the run; an early manual finish must be labelled with its actual count.
Compare median, p95 and spread together. A scheduling interruption can affect one value. Keep browser, connection, display settings and foreground state fixed, then repeat after one controlled change.
Need an automatic key-repeat rate instead? The keyboard repeat rate test measures intervals between repeat=true events during a hold. It measures neither physical polling nor event-to-frame latency.
Keep a refresh-rate observation beside any timing comparison. The monitor refresh rate test checks browser frame callbacks, not a game's frame time or complete display response.
Input lag, input delay and input latency compared
The value describes the page's recorded interval. A change across two otherwise matched browser runs needs repeating; it cannot identify which hidden hardware stage changed.
Does one run have a long tail? Compare p95 and spread, not only median. Frame scheduling and foreground activity affect the callback boundary. Non-overlapping summaries alone are not statistical proof of a physical device improvement.
At a nominal 60 Hz, one frame period is about 16.7 ms; at 120 Hz it is about 8.3 ms. Those are arithmetic periods, not milliseconds saved on every click. Actual callbacks and workload determine this browser's observed run.
The part of input lag a browser cannot see
The page cannot measure switch actuation, controller firmware, USB transport or physical panel response. It uses event timestamps and animation callbacks. Describe those endpoints instead of calling the result complete sensor-to-photon delay.
Timer precision and browser workload limit small comparisons. A one-millisecond change is not automatically a hardware fact, even when medians differ. Repeat the setup and record spread before assigning a cause.
Network input delay lies outside this local sample. An online game adds simulation, rendering and network paths that this browser page does not run. Do not use its number to diagnose server latency or the game's complete response chain.
How to reduce input lag
If browser settings repeatedly change the event-to-frame distribution under matched conditions, keep that observation and test the application separately. This method does not promise the same gain in a game engine.
If median and tail remain high, investigate local frame scheduling and workload before assigning blame to a keyboard or mouse. Display timing is one comparison, not a diagnosis of device report rate.
For physical input-to-light, use a method that observes actuation and display output. For online-game delay, use the game's own frame and network tools. The next test must match the endpoints you need.
Symptom table
| Symptom | Likely layer | Next action |
|---|---|---|
| Values much higher than reviews | Rendering pipeline is included | Compare configurations, not published figures |
| Wide spread between samples | Background load or frame pacing | Close other tabs and repeat in the foreground |
| No change after a mouse upgrade | Refresh rate dominates the total | Compare 60 Hz against a higher refresh mode |
Common questions
Can a browser measure real input lag?
A page measures the interval from event timestamp to animation callbacks. That is a browser observation, not complete physical input-to-light delay. It cannot see actuation, raw reports or panel light, so keep those endpoints separate.
Why is my browser latency result so much higher than a review?
A review may use another app and external hardware that observes physical motion and light. This page starts at a delivered event and ends at a callback. Different endpoints produce different numbers; neither alone validates the other or proves which hidden stage caused the difference.
Does a higher refresh rate reduce input lag?
A higher rate shortens nominal frame periods without promising fixed savings for every input. At 60 Hz a period is about 16.7 ms; at 120 Hz about 8.3 ms. Compare the observed browser runs under matched conditions and test the target app separately.
What is the difference between input lag and input delay?
Input lag and input delay are used for different endpoints, from device reporting to display response or network delay. Define the start and end before comparing values. This guide's tools cannot measure an online game's whole network path or physical key-to-photon response.