Window Sweaters treats its README as an instruction set for AI agents, not humans

Window Sweaters draws knitted borders around every window on your Mac. Not a drop shadow, not a highlight ring - actual rendered yarn patterns, with stitch textures and colourways picked by hand for 37 specific apps. Cursor gets one palette, Figma another, Discord its own. Apps outside the curated list borrow colours sampled from their own icons at runtime, softened into a two-colour zigzag, picnic, or twinkle pattern. The whole thing lives in your menu bar as a yarn icon.

The mechanism is worth understanding. It hooks into private macOS window APIs to track focus and position, which is why it needs Accessibility permission and why a system update could quietly break it. Borders disappear during window resizing and reappear when you let go - a known rough edge the author flags honestly. The app targets macOS 13 and later on both Apple Silicon and Intel, but the author is candid that Intel and older macOS versions haven't had the same hands-on testing. It's been tested on Apple Silicon with macOS 26.

Customisation goes deeper than the menu bar controls suggest. A plain text config file at ~/Library/Application Support/Knit Borders/apps.conf lets you assign any hex colour and named pattern to any app by prefix match. You can drop your own PNG stitch charts into the charts folder to replace built-in patterns entirely. There's also an optional shell script hook at startup if you want to drive things from the command line. The config directory still carries the app's original internal name - Knit Borders - so existing settings survive renaming.

The project builds on JankyBorders by Felix Kratz and is released under GPL-3.0. The build process is straightforward: Command Line Tools, Python 3, one shell script, one Python installer. The Makefile exposes a test runner, a catalogue renderer, and a renderer benchmark, which suggests the rendering path has been given real engineering attention rather than being left as a weekend hack.

What makes this interesting beyond the obvious charm is the installation note at the top of the README: the author suggests you can just hand the repo URL to a coding agent and ask it to install the app. That's a small but telling signal about where casual software distribution is heading - the README as an instruction set for an agent rather than a human, with the human as optional intermediary. The app itself is a delightful piece of desktop craft. That framing is the more quietly notable thing.