macos-capabilities_skill

Overview

This skill provides expert guidance on macOS platform capabilities, focusing on system integration features like sandboxing, app extensions, menu bar apps, and background execution. It distills practical rules, common pitfalls, and implementation patterns for developers building macOS apps with deep platform integration.

How this skill works

The skill inspects platform constraints and recommended APIs and maps them to concrete implementation choices: entitlements for the App Sandbox, lifecycle and communication models for app extensions and XPC, design patterns for menu bar apps, and appropriate use of launch agents and daemons for background work. It highlights which capabilities require entitlements, which run in-process versus out-of-process, and how to design secure, maintainable integrations.

When to use it

• Adding or auditing entitlements and sandbox rules for a macOS app
• Designing app extensions (Finder, Share, Today widget) or choosing XPC vs in-process APIs
• Building a menu bar app that must be lightweight and responsive
• Implementing background tasks that must survive app termination or run on system boot
• Choosing between launch agents and daemons for user vs system-level background services

Best practices

• Request the minimal entitlements necessary; prefer system-provided APIs over broad file access
• Isolate privileged logic in XPC services when interacting with user data or performing long-running tasks
• Keep menu bar apps responsive by offloading heavy work to background threads or XPC helpers
• Use launch agents for per-user background tasks and daemons for system-wide services; avoid unnecessary persistence
• Design clear communication contracts between app and extensions with versioning and graceful degradation

Example use cases

• Converting a full-featured app to run under the App Sandbox with appropriate file access and network entitlements
• Creating a Finder extension to add custom context-menu actions that communicate with the host app via XPC
• Developing a lightweight menu bar utility that shows quick status and launches the main app when needed
• Implementing a launch agent to perform periodic sync tasks for a user account without keeping the main app running
• Separating crash-prone or privileged subsystems into sandboxed XPC helpers to improve stability and security