Mist

A tiling window manager for macOS, built from the ground up as a modern, open, well-typed alternative to yabai / aerospace.

Status: functional. Scan → reconcile → tile → apply works against real windows. The float rule action applies, and hotkeys (focus_left/right/up/down, toggle_float) are wired through a CGEventTap. Config hot-reloads live.

Parsed and accepted, but not acted on: the monitor, workspace and layout rule actions run and write to the workspace and display stores, but nothing reads those stores, so they have no effect. always_on_top is recorded on the window model and never applied to the real window. animate and animation are parsed and have no effect.

One rough edge worth knowing: hotkey actions are raw strings, so a name Mist does not recognise — including a typo — binds successfully and then never fires, with only a debug line to say so.

Runtime needs Accessibility + Input Monitoring grants; the pure middleware is unit-verified.

Why

The existing options are either closed-source, abandoned, or sprawling C. Mist is:

• Open source — still free, still MIT-licensed.
• Type-safe — Swift enums/structs instead of stringly-typed config handling.
• Boring on purpose — the config is a file, mirrors are explicit, and complexity is actively fought.

Architecture

Two targets:

• MistCore — all logic, no AppKit. Parses config, computes layout, runs the engine, owns the events. Unit-testable headlessly.
• Mist — the macOS menu-bar app. Owns the accessibility connection and renders windows into the grid the engine computes.

Directory layout under Sources/MistCore/:

Accessibility/  Permission trust + monitor, window discovery (AX scan).
Animations/     Motion curves + reduce-motion support.
Core/           AppCoordinator, EventBus, Logger, MistError.
Configuration/  TOML parser, config loader/mapper, LayoutName.
Displays/       Display model + CG display-frame provider.
Hotkeys/        Hotkey model + parser + conflict-checking manager.
LayoutEngine/   BSP/stack/horizontal/vertical/monocle/floating.
Rules/          Rule, conditions, actions.
WindowManager/  Window model + manager, AX control (move/resize/focus), tiler, geometry.
Workspaces/     Workspace model + layout sharing.

Building

Requirements: macOS 14+, Swift 5.9+, Command Line Tools.

swift build            # debug
./Scripts/build-app.sh # assembles build/Mist.app (ad-hoc signed)

Tests

swift test is the target. Note: running the suite locally currently needs a full Xcode install (the CLI-only swift test lacks the testing backend in some CLT builds). The logic is verified headlessly via the release of a self-check harness; restore the suite once a normal toolchain is available.

Configuration

Config lives at ~/Library/Application Support/Mist/mist.toml (TOML, hot-reloaded). See Support/mist.toml for a commented example covering layout, gaps, hotkeys, and per-app rules.

Distribution

Mist ships as a real .app bundle (the repo is SwiftPM, no .xcodeproj) that the build script assembles from the compiled binary. Grab it with:

git clone <repo-url> && cd Mist
./Scripts/build-app.sh --release   # produces build/Mist.app
cp -R build/Mist.app /Applications/

No Homebrew, no casks — just clone, build, and drag it into /Applications.

Signing: ad-hoc by default. For public distribution set MIST_SIGNING_IDENTITY to a Developer ID and notarize (codesign --deep --options runtime).