Key chatter test

Key chatter — also called switch bounce or double-typing — occurs when a single physical tap on a key produces two or more discrete key presses. Inside a mechanical switch, two springy metal leaves press together to complete an electrical circuit. When the leaves strike each other, or when finger pressure fluctuates slightly near the actuation point, the metal contacts can rebound open for a few milliseconds before settling closed again.

This tester uses the browser's high-resolution monotonic clock (performance.now()) to measure the exact elapsed time in milliseconds between consecutive physical keydown events on the same key code. Any event where event.repeat === true is discarded, and a key cannot trigger a second measurement until its intervening keyup event has fired. Whenever the interval between two taps on the same key is less than or equal to your selected threshold (default 40 ms), the press is flagged as a chatter bounce.

To test a suspect key reliably, tap it 40 to 60 times at a relaxed, natural rhythm — roughly three to four taps per second — and vary your finger strike slightly (center press, off-center press, light tap, and slow release). Compare the shortest recorded interval against these practical ranges:

Worked example: if you tap a key at 5 taps per second, the average cycle time is 1000 ms ÷ 5 = 200 ms between presses. If the table suddenly records a 14 ms shortest interval, your finger did not move fourteen times faster for one tap — the switch contacts reopened and reclosed inside a single keystroke.

1. Rule out wireless interference and USB hubs: Dropped keyup packets on a congested 2.4 GHz dongle or unpowered USB hub can make keys repeat or stutter. Plug the keyboard directly into a rear motherboard USB port with a known-good data cable and retest.
2. Clean the switch with compressed air and 99% IPA: Unplug the keyboard, pull the keycap, depress the switch stem, and blow out dust with short bursts of compressed air. For unsealed mechanical switches, a single drop of 99% isopropyl alcohol (never 70% rubbing alcohol or household lubricants) worked in by pressing the stem 30 times can flush thin oxidation off the contact leaves. Let the switch dry completely for 15 minutes before reconnecting power.
3. Swap switches on a hot-swap PCB: If your board has hot-swap sockets, pull the chattering switch (for example on KeyE) and trade it with a rarely used key such as ScrollLock or Pause. While the switch is out, check that both metal pins are straight and that the hot-swap socket leaves underneath are not splayed apart. If the chatter moves to ScrollLock, the switch itself is worn; if KeyE keeps chattering with a fresh switch, inspect the PCB socket solder joints.
4. Increase firmware debounce time: Most keyboards set a hardware debounce window of 5 ms. Gaming software that lowers debounce to 1 ms or 2 ms frequently exposes normal mechanical contact bounce. In QMK (#define DEBOUNCE 10), ZMK (debounce-press-ms and debounce-release-ms), or your manufacturer's utility, raise the debounce window to 10 ms or 12 ms. On analog Hall-effect boards, widen the rapid-trigger release deadzone by 0.15 mm – 0.25 mm.

Need to check whether a key registers at all or stays stuck down? Use the visual keyboard tester or the keyboard rollover test. To learn how switch internals affect contact bounce, read keyboard switch types explained and keyboard not working fixes. Once your switches are clean, measure your speed on the typing test or check your score math with the WPM calculator.