FocusBlur

A native macOS menu-bar app that blurs all background windows, keeping only the focused window sharp — similar to Monocle.

Requirements: macOS 26 (Tahoe) or later, Swift 6+

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Building manually

1. Clone the repository

git clone <repo-url>
cd <repo>

2. Build a release binary

swift build -c release

The compiled binary lands at:

.build/release/FocusBlur

3. Create the .app bundle

mkdir -p FocusBlur.app/Contents/MacOS
mkdir -p FocusBlur.app/Contents/Resources

cp .build/release/FocusBlur FocusBlur.app/Contents/MacOS/
chmod +x FocusBlur.app/Contents/MacOS/FocusBlur

4. Write Info.plist

cat > FocusBlur.app/Contents/Info.plist << 'EOF'
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <key>CFBundleExecutable</key><string>FocusBlur</string>
    <key>CFBundleIdentifier</key><string>com.local.FocusBlur</string>
    <key>CFBundleName</key><string>FocusBlur</string>
    <key>CFBundlePackageType</key><string>APPL</string>
    <key>CFBundleShortVersionString</key><string>1.0</string>
    <key>NSPrincipalClass</key><string>NSApplication</string>
    <key>NSHighResolutionCapable</key><true/>
    <key>LSUIElement</key><true/>
    <key>NSAccessibilityUsageDescription</key>
    <string>FocusBlur needs Accessibility access to detect which window is focused.</string>
</dict>
</plist>
EOF

5. Ad-hoc codesign

codesign --sign - --force --deep FocusBlur.app

6. Install and run

cp -r FocusBlur.app /Applications/
open /Applications/FocusBlur.app

Updating an existing install (rebuild + redeploy in one step)

swift build -c release && \
  pkill -x FocusBlur; sleep 0.3; \
  cp .build/release/FocusBlur /Applications/FocusBlur.app/Contents/MacOS/FocusBlur && \
  codesign --sign - --force --deep /Applications/FocusBlur.app && \
  open /Applications/FocusBlur.app

---

First launch

macOS will prompt for Accessibility permission — this is required to detect which window is focused. Go to:

System Settings → Privacy & Security → Accessibility → enable FocusBlur

The blur activates automatically within one second of granting permission. No Screen Recording permission is needed.

---

How it works

• Window detection — AXUIElement Accessibility API tracks the frontmost window via AXObserver notifications (event-driven, ~0.1% CPU idle)
• Blur overlay — stacked NSVisualEffectView layers with simultaneous alpha control; multiple passes compound to produce a heavy opaque blur without private APIs or Screen Recording
• Overlay positioning — the overlay window sits at .normal level and is placed just below the focused window via order(.below, relativeTo: windowID); the focused window occludes the blur naturally
• Auto-focus fallback — when the frontmost app has no visible windows (all minimized), CGWindowListCopyWindowInfo finds the topmost visible window of the next app on screen and anchors to that instead
• Mouse wiggle — rapid back-and-forth shake (3+ direction reversals in 600 ms) toggles the blur on/off

---

Project structure

.
├── Package.swift
├── README.md
├── .gitignore
└── Sources/FocusBlur/
    ├── FocusBlurApp.swift          # @main, AppDelegate, menu bar setup
    ├── Models/
    │   └── AppSettings.swift       # Persisted user settings
    ├── Services/
    │   ├── BlurOverlayWindow.swift # NSWindow subclass — stacked blur layers
    │   ├── WindowManager.swift     # AX tracking, overlay lifecycle
    │   └── MouseShakeDetector.swift
    └── Views/
        └── ContentView.swift       # Liquid glass settings panel