DoubleKey

Stop your Mac keyboard from typing letters twice.
A tiny menu bar app that blocks key chatter. No setup, no per-key tuning, no CPU use.

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Worn keyboards, and especially the MacBook butterfly keyboards from 2015 to 2019, often register one key press as two: you type hello and get heello. This is called key chatter. DoubleKey sits in the menu bar and silently drops the extra press before any app sees it.

It's inspired by Unshaky. The difference: DoubleKey works on every key out of the box, so you don't have to find and set up each faulty key.

Features

• Zero setup. Install, allow Accessibility access once, forget about it.
• Every key covered. No per-key list to maintain.
• Very light. About 220 KB on disk and 12 MB of memory. It does no work between keystrokes: no timers, no polling, no background threads of its own.
• Private. It has no network code. Key presses are never stored, logged or sent anywhere; it only remembers when each key was last released.
• Starts at login by itself.
• Universal. Runs natively on Apple Silicon and Intel Macs, macOS 13 Ventura or later.

Install

Download

1. Get DoubleKey.zip from the latest release, unzip it and move DoubleKey to Applications.

2. The app isn't notarized by Apple, so macOS blocks the first launch. Open it once, then go to System Settings → Privacy & Security, scroll down and click Open Anyway. Or run this instead:

   xattr -dr com.apple.quarantine /Applications/DoubleKey.app

3. When macOS asks, allow Accessibility access in System Settings → Privacy & Security → Accessibility. DoubleKey starts working within 2 seconds; no restart needed.

A keyboard icon appears in the menu bar. It's greyed out while DoubleKey is paused or still waiting for permission.

Build from source

You need the Xcode Command Line Tools (xcode-select --install).

git clone https://github.com/fpvromadm/doublekey.git
cd doublekey
./build.sh install

This builds the app, copies it to /Applications and starts it.

Usage

Click the keyboard icon in the menu bar:

Menu item	What it does
Blocked N double presses	How many presses were dropped since the app started
Enabled	Pause or resume filtering
Threshold	How close two presses must be to count as chatter (20–100 ms, default 40)
Launch at Login	Start DoubleKey when you log in (on by default)
Quit DoubleKey	Stop it

Still getting double letters? Raise the threshold to 50, 60 or 80 ms. Losing letters you meant to type twice? Lower it to 30 ms.

How it works

A key press goes down then up. A chattering switch makes extra contact right after you let go, so the system sees down, up, down, up for a single press.

DoubleKey installs a keyboard event tap and applies one rule:

If a key goes down less than threshold ms after the same key went up, and no other key was pressed in between, drop that press and its release.

Even fast typists take far longer than 40 ms between releasing a key and pressing it again, so real double letters like ll or ee go through. Held keys and auto-repeat are never touched. Modifier keys (⌘ ⌥ ⌃ ⇧) are not filtered.

The whole logic is about 40 lines in Sources/Debouncer.swift, with tests in Tests/main.swift.

Development

./build.sh          # build build/DoubleKey.app
./build.sh test     # run the debounce tests
./build.sh install  # build, copy to /Applications and start

No Xcode project: it's plain swiftc and a shell script.

Keeping the Accessibility permission across rebuilds. macOS ties the permission to the app's code signature. By default build.sh signs ad-hoc, so after each rebuild you need to remove DoubleKey from the Accessibility list and add it again. To avoid that, create a local signing certificate once:

./scripts/make-signing-cert.sh

It creates a self-signed "DoubleKey Local Signing" certificate in your login keychain, trusted for code signing only, and build.sh uses it from then on. You can also set SIGN_ID to any identity you already have.

Releases. Pushing a tag like v1.1 builds the app on GitHub Actions and attaches DoubleKey.zip to a new release.

Uninstall

1. Click the menu bar icon → Quit DoubleKey.

2. Delete /Applications/DoubleKey.app.

3. Remove DoubleKey from System Settings → Privacy & Security → Accessibility and from General → Login Items.

4. Optionally delete its settings:

   defaults delete io.github.fpvromadm.doublekey

License

MIT