What is keyboard chatter?
Chatter is when a single physical press produces two or more registered keystrokes. Mechanical switches close their contacts by bouncing them together; firmware applies a debounce window (typically 5 to 15 ms) to ignore the bounce. When a switch wears out, gets contaminated by dust or oxidation, or the debounce algorithm is too aggressive, the second bounce slips through as a second keypress. The result is words like 'helllo' or 'thee' appearing from a clean single tap. DeviceCheckOnline times the gap between consecutive keydown events and flags anything below the chatter threshold.
How does this tool detect chatter?
The page records every keydown timestamp and computes the delta between consecutive presses of the same key. A normal human double-tap is at least 80 to 120 ms apart; switch chatter typically fires within 5 to 40 ms, well under the speed any finger can repeat. Tap each suspect key two or three dozen times and watch the log. Any interval under roughly 50 ms with no intentional double-tap is almost certainly bounce. The closer the interval to single-digit milliseconds, the more confident the diagnosis.
My E key types 'ee' sometimes. How do I fix it?
First confirm it is chatter and not a sticky key by running the test here. If confirmed, options in order of effort: (1) blow compressed air into the switch, (2) on hot-swap boards pull the switch and clean the contacts with isopropyl alcohol or replace it, (3) on soldered boards, some firmware (QMK, VIA, manufacturer software) lets you raise the per-key debounce time, (4) Windows users can enable Filter Keys as a software workaround, though it adds input lag. A failing switch usually only gets worse.
What's the difference between chatter and a stuck key?
Chatter produces multiple discrete keydown/keyup pairs from one tap — you see 'aa' but each 'a' is a separate event. A stuck key produces one keydown without a matching keyup, so the OS thinks you are holding the key and the autorepeat kicks in, producing 'aaaaaaaaaaa'. Use /keyboard/tester to see whether a held key fills and stays filled (normal) or empties and refills rapidly (chatter) or never empties (stuck). The /keyboard/repeat tool shows the autorepeat behaviour.
Can chatter happen on membrane or laptop keyboards too?
Yes. Although chatter is most associated with mechanical switches, rubber-dome and scissor-switch keyboards can also double-register when the contact dome cracks, a trace corrodes, or liquid residue bridges the membrane layers. Laptop keyboards are harder to service — you typically replace the whole key module or the entire keyboard assembly. Test with an external USB keyboard to confirm the chatter follows the hardware rather than the OS, then decide whether to repair, RMA or replace.
Why does the chatter test require many repeated taps?
Switch failures are often intermittent. A degraded switch may register cleanly nine times and chatter on the tenth, because the bounce profile depends on actuation speed, angle and contact alignment. A short sample misses the failure. Tap each key 30 to 50 times at varied cadence to give the switch enough trials. If the chatter rate is one in twenty or worse, the switch is unreliable and warrants replacement. Pair this with /keyboard/rollover to verify the rest of the matrix is healthy.