How to test for chatter
Type normally for a minute so every key gets used, then pick any key that has typed double and press it 20 to 30 times at your usual speed. Each press of a key is compared with the previous press of the same key. A gap below the threshold (40 ms unless you change it) is flagged: people can’t press one key twice that fast, so the second press came from the switch.
The histogram shows every repeat under 100 ms in 5 ms steps, with bars under the threshold in red. A healthy keyboard leaves the left side empty; chatter shows up as a cluster at 5–30 ms. The table lists every key you pressed at least twice with its fastest repeat, so a key that only chatters now and then still stands out.
Changing the threshold
40 ms suits most keyboards. Lower it to 20–30 ms if you’re a fast typist and fast double letters get flagged, or raise it to 60 ms to catch a switch that bounces slowly. Changing it re-checks all the presses so far.
Fixing it
Cleaning is the first step: pull the keycap, blow compressed air around the switch, and press it many times. Laptops and low-profile boards shouldn’t be sprayed with liquid; a technician can open them.
Debounce is the next lever. In QMK firmware it’s the DEBOUNCE setting in the keyboard’s config.h, 5 ms by default; building the firmware with 10–15 ms hides most chatter at the cost of a few milliseconds of delay. VIA doesn’t expose debounce; Vial and QMK do, Vial without rebuilding the firmware, and some manufacturers’ own apps have a debounce or “anti-chatter” option. On hot-swap boards, replacing the one switch is cheap and permanent.
If the keyboard is under warranty, don’t open it: send the tester’s report, which lists each key and its fastest gap.
Reading a repeat gap
The table in the tester shows each key’s fastest repeat. This is what those numbers usually mean.
| Fastest repeat | Likely cause |
|---|---|
| under 10 ms | The contacts bounce and the debounce time is too short to hide it. Almost always the switch or its firmware setting. |
| 10–40 ms | A worn, dirty or oxidised switch that opens and closes again during one press. The classic chatter a detector should flag. |
| 40–80 ms | A grey zone: very fast double taps land here too. Suspect chatter only if it happens when you pressed once. |
| over 80 ms | A second press by your finger. Not chatter. |