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Double Typing Test

Type normally and this page measures the gap between repeat presses of the same key in milliseconds. Anything faster than a human can tap is switch chatter.

Flag gaps under

Start typing

Anywhere on this page. Real sentences for at least a minute give the most reliable result.

Presses

Chatter events

Chatter rate

0.0%

Sample

Thin

How Chatter Detection Works

A keyboard that types double letters almost always has one bouncing switch. Mechanical switches close a physical contact, and a worn or dirty contact does not close cleanly — it makes and breaks several times within a few milliseconds. The keyboard's controller is supposed to filter that out with a debounce window, typically five milliseconds. When a switch degrades far enough that its bounce outlasts the debounce window, the controller reports two presses for one push. That is chatter.

This page finds it by timing. Every keydown is stamped with a high-resolution timestamp, and for each key we measure the gap to that same key's previous press. Human limits give us a clean cutoff: the fastest deliberate double-tap of one finger lands around 80 to 100 milliseconds, and even a trained drum-roll with two fingers on one key rarely goes below 50. So a gap of 30 milliseconds or less on the same key is not something you did. It is the hardware.

Type for at least a minute of normal text before you trust the result. Chatter is intermittent by nature — a switch that fails one press in fifty will not show up in a dozen keystrokes, and a short sample can just as easily produce a false clean bill of health as a false alarm. The counter tells you when there is enough data.

The threshold is adjustable because different situations need different strictness. 10ms is the conservative setting — a hit at that gap is unambiguous hardware failure with no plausible human explanation. 30ms is the default and the right general-purpose choice. 50ms catches marginal switches that are starting to go, at the cost of occasionally flagging a genuine fast double-tap, so read those hits alongside what you were actually typing.

Two honest limitations. Auto-repeat from a held key is excluded — the browser marks those events and we skip them — so holding a key down will never register as chatter, correctly. And browsers deliberately coarsen their high-resolution timestamps to make fingerprinting harder: Firefox rounds to whole milliseconds without cross-origin isolation, Chrome to roughly a tenth of one. That is fine for a 30-millisecond threshold and meaningless below about two, so do not read significance into a reported gap of 1ms versus 2ms.

If the report comes back clean but your keyboard still misbehaves, the fault is probably elsewhere. Keys that fire continuously belong in the stuck key test; keys that drop out under load belong in the ghosting test; and a general sweep for dead keys is what the full keyboard test is for.

Key Capabilities & Features

Millisecond-resolution timing

Uses high-resolution event timestamps rather than whole-millisecond clocks, so short bounces are visible.

Per-key report

Names the offending key, how many times it chattered, and its worst gap — so you know which switch to replace.

Three thresholds

10ms for certainty, 30ms for everyday use, 50ms to catch a switch that is starting to fail.

Auto-repeat excluded

Holding a key down produces a stream of events. Those are filtered out, so they cannot fake a result.

Sample-size warning

Tells you when you have typed enough for the result to mean anything, instead of declaring a clean board after six keystrokes.

Works on any keyboard

Mechanical, membrane, laptop or external — chatter is measured from the events, not the switch type.

How to Perform This Test

Click once on the page so the browser tab has keyboard focus.:
Leave the threshold at 30ms for a first run.:
Type normally for at least a minute — real sentences, not random mashing. A paragraph of anything you know by heart works well.:
Deliberately use the key you suspect. If your E doubles, type words full of Es.:
Read the per-key table. One key with several hits is a failing switch; scattered single hits across many keys usually means you were typing quickly.:
Drop the threshold to 10ms to confirm. Hits that survive at 10ms have no human explanation at all.:

Troubleshooting Common Hardware Issues

No hits at all after a minute of typing: good news — your switches are debouncing correctly. If letters still double, suspect software rather than hardware.
Hits on every key you touch: the threshold may be too generous for your typing speed. Drop to 10ms and see which survive.
Reported gaps of exactly 1ms or 0ms: your browser is rounding timestamps for privacy. The hit is still real; the precise number is not.
Holding a key produces no hits: correct. Auto-repeat is excluded because it is the operating system repeating, not the switch bouncing.
The same key chatters here but not in a text editor: some applications apply their own input filtering. This page reports raw events, which is what you want for diagnosis.
Every key on the board chatters at once: check for remapping software, a macro layer, a KVM switch or remote-desktop software. Twenty switches do not fail simultaneously.
Chatter only appears when the keyboard warms up: a known failure mode. Thermal expansion moves a marginal contact just enough. It will get worse — replace the switch.

Reading the Gap: What Each Range Means

The number that matters is the gap between two presses of the same key. Here is how to interpret it.

Gap	Verdict	What to do
Under 5ms	Definite chatter	Inside the debounce window itself. The switch is failing badly — replace it.
5 – 15ms	Almost certainly chatter	No human produces this. Clean or replace the switch.
15 – 30ms	Chatter	Well below any deliberate tap. Worth acting on, especially if one key dominates.
30 – 50ms	Suspicious	Possible with a two-finger roll on one key. Check what you were typing.
50 – 100ms	Probably you	A fast deliberate double-tap lives here. Not flagged by default.
Over 100ms	Normal typing	Ordinary double letters like the two Ls in "hello".

Pay attention to concentration as well as count. Twenty hits spread evenly across twenty different keys usually means you were typing fast and the threshold is set generously. Twenty hits on one key means that switch is broken. The per-key table above sorts by count for exactly this reason.

Fixing a Key That Types Double Letters

Chatter is a hardware fault, but it is one of the more fixable ones. Work down this list — the first two steps resolve a good proportion of cases and cost nothing.

Blow it out. Pull the keycap and use compressed air at the switch from a couple of angles, then retest. Dust and skin debris between the contacts is the single most common cause, and it is genuinely often this simple.
Clean the contacts with isopropyl alcohol. A few drops of 99% IPA into the switch, then work it fifty times with the stem to scrub the contacts. Let it dry fully before powering on. This revives a lot of switches that air alone will not.
Swap the switch. On a hot-swap board, pull the old switch with a puller and press in a new one — a two-minute job with no soldering. On a soldered board it needs desoldering, which is a bigger commitment but still cheaper than a new keyboard.
Raise the debounce time in firmware. If your board runs QMK or VIA, increasing DEBOUNCE from 5ms to 10 or 15ms will mask most chatter at the cost of a small amount of latency. This is a workaround rather than a repair, but it is the right answer when the switch is soldered and you are not ready to open the board.
Check for software doubling first if every key is affected. Chatter on one or two keys is hardware. Chatter across the whole board at once is almost never twenty simultaneous switch failures — look at a remapping tool, a macro layer, a virtual KVM, or remote-desktop software echoing your input.

On a membrane keyboard, chatter usually means the rubber dome has torn or the conductive trace has worn through, and there is no practical repair for a single key. Those boards are replaced rather than fixed.

One last diagnostic worth doing before you buy anything: plug the keyboard into a different computer and run this test again. Chatter that follows the keyboard is the keyboard. Chatter that stays behind on the original machine is software.

Frequently Asked Questions

Why is my keyboard typing double letters?

One switch is chattering. The physical contact inside it is not closing cleanly, so it makes and breaks several times in a few milliseconds and the keyboard reports two presses for one push. Type on this page for a minute and the per-key table will name the key doing it.

What is key chatter?

Chatter, or bounce, is a switch registering multiple presses from a single push. All keyboards bounce slightly; the controller filters it with a debounce window of around five milliseconds. Chatter is what happens when a worn or dirty switch bounces for longer than that window.

How do I know it is the keyboard and not my typing?

By the gap. The fastest deliberate double-tap of one key is about 80 to 100 milliseconds. This test flags gaps under 30 by default and you can tighten it to 10, which is physically impossible for a human. Anything caught at 10ms is the hardware.

Can key chatter be fixed?

Often, yes. Compressed air into the switch fixes many cases, and flushing the contacts with 99% isopropyl alcohol fixes more. If neither works, a hot-swap board takes a new switch in about two minutes. On QMK or VIA firmware you can also raise the debounce time as a workaround.

How long should I type before trusting the result?

At least a minute of ordinary text, and longer if the problem is intermittent. A switch that fails one press in fifty will not appear in a handful of keystrokes. The page tells you when the sample is large enough.

Why does the test say 0ms or 1ms for a gap?

Browsers round their high-resolution timestamps to limit fingerprinting — Firefox to a whole millisecond, Chrome to about a tenth. The detection is unaffected at a 30ms threshold, but do not read meaning into the difference between a reported 1ms and 2ms.

Does this test work for membrane and laptop keyboards?

Yes — it measures the events, so any keyboard works. The repair options are narrower: a membrane sheet or a laptop butterfly switch cannot practically be replaced for one key, so a confirmed chatter there usually means replacing the keyboard or using firmware-level debounce if available.

Could double letters be a software problem instead?

Yes, and there is a clean tell: hardware chatter affects one or two keys, while software doubling affects all of them. If every key doubles, look at remapping tools, macro software, a KVM switch, or remote-desktop software echoing your keystrokes.

Keyboard Layouts

Hardware Diagnostics

Individual Key Tests

Speed & Sound