Probo

macOS menu bar utility that rewrites each mouse-wheel notch to a fixed line step. Trackpad input, momentum, and gesture phases pass through untouched.

Features

• Fixed step per notch: Slow (2 lines) or Medium (3 lines)
• Option-key precision drops to 1 line per notch
• Terminal heuristic emits 1 line per notch in terminal apps, configured step when Option is held
• Natural scroll-direction toggle
• Mouse button 4 maps to the macOS Look Up gesture
• Optional sleep-prevention assertion while enabled; display sleep, lid close, and manual sleep still fire
• Launch at login via SMAppService
• Pass-through for continuous, phased, diagonal, and zero-delta events

Settings live in a single window opened from the menu bar icon.

Requirements

• macOS 15+
• Apple silicon (arm64)
• Accessibility permission

Install

Download the signed arm64 archive from Releases and drop Probo.app into /Applications.

First launch routes through the menu bar icon. Enabling Probo or selecting Request Access opens System Settings > Privacy & Security > Accessibility; the event tap installs as soon as macOS reports the grant.

Build

Requires Xcode command-line tools. Local builds codesign with a self-minted identity created on first run.

scripts/dev/run.sh

Writes build/Probo.app and relaunches it. Set PROBO_CODESIGN_IDENTITY=- for ad-hoc signing.

Architecture

AppKit owns the menu bar item, status menu, settings window, and settings controls over a native Swift rewrite core. The event-tap callback reads raw CGEvent fields, applies the terminal heuristic, asks the core for a rewrite decision, and synthesizes a replacement scroll event when needed. Hot path is allocation-free.

Layer	Path	Role
App	probo/Sources/App	Lifecycle, controller wiring
Core	probo/Sources/Core	Pure rewrite hot path
Events	probo/Sources/Events	Event tap, scroll synthesis
Configuration	probo/Sources/Configuration	Settings model, persistence
System	probo/Sources/System	Accessibility, frontmost app, sleep, login
UI	probo/Sources/UI	Status menu and settings controls
Tools	probo/Tools	Probes, diagnostics

Development

No SwiftPM manifest, no Xcode project. Shell scripts drive every workflow.

Script	Purpose
swift-format format -i -r probo/Sources probo/Tests	Format sources and tests
scripts/test.sh	Build and run BDD-style Swift tests
scripts/build.sh	Build and codesign the bundle (shared with CI)
scripts/dev/run.sh	Build and relaunch Probo.app
scripts/dev/lsp.sh	Generate compile_commands.json for SourceKit-LSP
scripts/dev/setup-codesign.sh	Create local signing identity
scripts/profiling/hot-path.sh	Hot-path micro profiles or xctrace recordings
scripts/ci/mint-identity.sh	Emit p12 and passphrase for CI signing secrets

Re-run scripts/dev/lsp.sh after source-layout or compiler-flag changes so the IDE matches the shell build.

Release

CI runs on every push and pull request. CD publishes a rolling latest GitHub release with a signed arm64 archive after CI passes on main.

Release signing reads PROBO_RELEASE_P12_BASE64 and PROBO_RELEASE_P12_PASSWORD. Missing either falls back to an ad-hoc signature with a warning.

License

MIT