Resizer

A native macOS app that resizes any application's window to exact pixel dimensions. Works with any app — and when a browser (Chrome, Safari, Edge, Arc, Brave) is the target, it also offers viewport-accurate sizing.

No extensions, no dependencies — just a lightweight native Swift app.

Install

Option A: Download the installer

1. Download Resizer-1.0.pkg from the latest release
2. Double-click to install (installs to /Applications)
3. Drag Resizer to your Dock for easy access

Option B: Build from source

git clone https://github.com/danbgordon/resizer.git
cd resizer
chmod +x build.sh
./build.sh

First Launch

1. Right-click → Open the first time to bypass Gatekeeper
2. Grant Accessibility permission when prompted — this is the only permission needed for window resizing, and it works for all apps

How to Use

1. Click on the window you want to resize
2. Launch Resizer from the Dock
3. Pick a size from the dropdown and click Resize
4. Done — the window resizes and the app exits

If the target is a browser, viewport options are also shown (e.g., "1280 × 1024 (viewport)").

Custom Sizes

Sizes are stored in ~/.config/resizer/sizes.conf (created automatically on first launch). Edit this file to add your own presets:

# Resizer — custom sizes
# Format: width,height or width,height,name (one per line)
# Lines starting with # are ignored, blank lines are skipped
1280,1024
1920,1080,Full HD
1440,900,Recording
3840,2160,4K

Changes take effect the next time you launch the app.

Window vs Viewport Mode

• Window mode — sets the full window frame (including title bar, tabs, address bar) to the target dimensions. Available for any app.
• Viewport mode — sets the web content area to the exact target dimensions, automatically compensating for the browser's UI chrome. Only available for supported browsers.

Supported browsers for viewport mode: Google Chrome, Chrome Canary, Chromium, Brave, Microsoft Edge, Arc, Safari.

Chrome viewport setup: Enable View → Developer → Allow JavaScript from Apple Events (one-time setting). Viewport mode also requires a regular web page in the active tab — not a chrome:// internal page.

Permissions

Action	Permission	When prompted
Resize any window	Accessibility	Once, on first launch
Browser viewport mode	Automation (per browser)	Once per browser, only if you use viewport mode

Resizer explains each permission before macOS prompts you.

Deployment (Fleet, Jamf, etc.)

1. Download or build Resizer-1.0.pkg
2. Deploy via MDM to /Applications
3. Optionally pre-approve Accessibility via a PPPC profile for com.danbgordon.resizer

How It Works

Resizer is a native Swift app that:

1. Detects the previously-active app using lsappinfo (skips Finder, Dock, and other launchers)
2. Reads sizes from ~/.config/resizer/sizes.conf (falls back to built-in defaults if missing)
3. Shows a size picker (with viewport options for browsers)
4. Resizes the window using the macOS Accessibility API (AXUIElement)
5. For viewport mode: measures the actual viewport via JavaScript, calculates the browser chrome overhead, and adjusts the window to compensate
6. Keeps the window on its current screen (multi-monitor aware)

Troubleshooting

"App is damaged and can't be opened" → Right-click the app → Open → click "Open" in the dialog. This is Gatekeeper; it only happens once.

Wrong app detected → Make sure you click on the target window before launching Resizer. If you launched from Finder, the app skips Finder and detects the next most recent app.

Window doesn't fit on my screen → 1920×1080 requires at least a 1920px-wide display. Add a smaller preset to your config file.

Viewport mode isn't offered → Viewport mode only appears when the target app is a supported browser.

Viewport falls back to window size → Make sure the active tab has a regular web page (not chrome://settings or similar). For Chrome, enable View → Developer → Allow JavaScript from Apple Events.