core-data-expert

The Core Data Expert skill provides fast, production-oriented guidance for building correct and performant Core Data stacks on iOS and macOS platforms. It specializes in diagnosing and fixing common Core Data crashes, threading issues, and performance bottlenecks. The skill focuses on practical, actionable advice rather than theoretical concepts, helping developers quickly identify problems and implement robust solutions.

This skill covers the full spectrum of Core Data development including stack setup with proper merge policies, fetch requests with NSFetchedResultsController, context management across view and background contexts, batch operations with persistent history tracking, schema migrations (lightweight, staged, and deferred), and CloudKit synchronization with NSPersistentCloudKitContainer. It emphasizes correct threading patterns using NSManagedObjectID for cross-context communication and provides specific guidance for Swift Concurrency integration with async/await and actors.

The skill is designed for iOS and macOS developers working with Core Data at any level—from those setting up their first persistent stack to experienced engineers debugging complex merge conflicts or optimizing fetch performance. It includes comprehensive references for common error scenarios like cross-context exceptions, migration failures, Sendable compliance issues, and batch operations that don't trigger UI updates. The skill's triage-first approach helps developers quickly route to the right solution based on their specific context, deployment target, and error patterns.