// Use when working with ANY data persistence, database, storage, CloudKit, migration, or serialization. Covers SwiftData, Core Data, GRDB, SQLite, CloudKit sync, file storage, Codable, migrations.
| name | axiom-data |
| description | Use when working with ANY data persistence, database, storage, CloudKit, migration, or serialization. Covers SwiftData, Core Data, GRDB, SQLite, CloudKit sync, file storage, Codable, migrations. |
| license | MIT |
You MUST use this skill for ANY data persistence, database, storage, CloudKit, or serialization work.
Use this skill when working with:
| Symptom / Task | Reference |
|---|---|
| SwiftData @Model, @Query, ModelContext | See skills/swiftdata.md |
| SwiftData schema migration, VersionedSchema | See skills/swiftdata-migration.md |
| SwiftData migration crashes, data loss | See skills/swiftdata-migration-diag.md |
| Migrating from Realm to SwiftData | See skills/realm-migration-ref.md |
| SwiftData vs SQLiteData decision | See skills/sqlitedata-migration.md |
| GRDB queries, ValueObservation, DatabaseMigrator | See skills/grdb.md |
| GRDB performance, indexes, EXPLAIN QUERY PLAN, cursors | See skills/grdb-performance.md |
| Full-text search (FTS5) in GRDB or SQLiteData | See skills/sqlite-fts-ref.md |
| GRDB shared across app + widget/extension (App Group) | See skills/grdb-app-groups.md |
| SQLiteData @Table, CRUD, SyncEngine | See skills/sqlitedata.md |
| SQLiteData advanced patterns, CTEs, views | See skills/sqlitedata-ref.md |
| Core Data stack, relationships, concurrency | See skills/core-data.md |
| Core Data migration crashes, thread errors | See skills/core-data-diag.md |
| ANY schema migration safety | See skills/database-migration.md |
| Codable, JSON encoding/decoding | See skills/codable.md |
| Cloud sync architecture, offline-first | See skills/cloud-sync.md |
| CloudKit, CKSyncEngine, CKRecord | See skills/cloudkit-ref.md |
| iCloud Drive, ubiquitous containers | See skills/icloud-drive-ref.md |
| Cloud sync errors, conflict resolution | See skills/cloud-sync-diag.md |
| Storage strategy, where to store data | See skills/storage.md |
| Storage issues, files disappeared | See skills/storage-diag.md |
| Storage management, disk pressure | See skills/storage-management-ref.md |
| Keychain / secure credential storage | See axiom-security (skills/keychain.md) |
| Keychain errors (errSecDuplicateItem) | See axiom-security (skills/keychain-diag.md) |
| Keychain API reference | See axiom-security (skills/keychain-ref.md) |
| Encryption / signing / key management | See axiom-security (skills/cryptokit.md) |
| CryptoKit API reference | See axiom-security (skills/cryptokit-ref.md) |
| File protection, NSFileProtection | See axiom-security (skills/file-protection-ref.md) |
| tvOS data persistence (no local storage) | See axiom-swift (skills/tvos.md) |
| tvOS + CloudKit SyncEngine | See skills/sqlitedata.md |
Core Data audit → Launch core-data-auditor agent or /axiom:audit core-data (safety violations, architectural gaps — migration options, thread-confinement, N+1 queries, merge policies, context isolation)
Codable audit → Launch codable-auditor agent or /axiom:audit codable (safety violations, semantic gaps — try? swallowing errors, JSONSerialization, date handling, silent field drops, wrapper-hidden fallbacks, cross-file strategy drift, enum future-case crashes)
iCloud audit → Launch icloud-auditor agent or /axiom:audit icloud (entitlement checks, file coordination, incomplete CKError matrix coverage, missing account-change observation, polling vs CKSubscriptions, SwiftData + CloudKit unsupported features, compound risks like uncoordinated I/O across extensions)
Storage audit → Launch storage-auditor agent or /axiom:audit storage (wrong file locations, missing backup exclusions, sensitive data on disk vs Keychain, missing App Group containers, unbounded cache growth, orphan files, compound risks like user data in tmp/ + critical content)
Database schema audit → Launch database-schema-auditor agent or /axiom:audit database-schema (unsafe ALTER TABLE, DROP operations, missing idempotency, FK constraints declared but not enforced, incomplete upgrade paths, compound risks like INSERT OR REPLACE on FK-referenced tables)
GRDB performance audit → Launch grdb-performance-auditor agent or /axiom:audit grdb-performance (raw SQL string interpolation, missing FK indexes in raw SQL, missing PRAGMA optimize for raw-GRDB apps, journal mode mismatch for app-group DBs, missing observesSuspensionNotifications for shared DBs, prefix-redundant indexes in raw SQL, legacy Record subclass)
SwiftData audit → Launch swiftdata-auditor agent or /axiom:audit swiftdata (struct models, missing schema registration, array relationships without defaults, background context misuse, N+1 patterns, stale predicates, CloudKit conformance gaps, compound risks like struct model + array relationship)
skills/swiftdata.md, skills/swiftdata-migration.mdskills/core-data.md, skills/core-data-diag.mdskills/grdb.md
3a. GRDB perf, slow query, schema design for perf? → skills/grdb-performance.md
3b. FTS5 (full-text search, any layer)? → skills/sqlite-fts-ref.md
3c. DB shared across app + extension/widget/Live Activity? → skills/grdb-app-groups.mdskills/sqlitedata.md, skills/sqlitedata-ref.mdskills/database-migration.md (ALWAYS — prevents data loss)skills/realm-migration-ref.mdskills/sqlitedata-migration.mdskills/cloud-sync.mdskills/cloudkit-ref.mdskills/icloud-drive-ref.mdskills/cloud-sync-diag.mdskills/codable.mdskills/storage.md, skills/storage-diag.md, skills/storage-management-ref.mdskills/sqlitedata.md (CloudKit SyncEngine)/skill axiom-concurrency/skill axiom-ai| Thought | Reality |
|---|---|
| "Just adding a column, no migration needed" | Schema changes without migration crash users. database-migration prevents data loss. |
| "I'll handle the migration manually" | Manual migrations miss edge cases. database-migration covers rollback and testing. |
| "Simple query, I don't need the skill" | Query patterns prevent N+1 and thread-safety issues. The skill has copy-paste solutions. |
| "CloudKit sync is straightforward" | CloudKit has 15+ failure modes. cloud-sync-diag diagnoses them systematically. |
| "I know Codable well enough" | Codable has silent data loss traps (try? swallows errors). codable skill prevents production bugs. |
| "I'll use local storage on tvOS" | tvOS has NO persistent local storage. System deletes Caches at any time. See axiom-swift (skills/tvos.md) for the iCloud-first pattern. |
| "UserDefaults is fine for this token" | UserDefaults is unencrypted, backed up to iCloud, and visible to MDM profiles. One audit catches it. keychain stores tokens securely. |
| "I'll encrypt it myself with CommonCrypto" | CryptoKit replaced CommonCrypto's buffer-management nightmares with one-line APIs. cryptokit prevents misuse. |
ALWAYS read skills/database-migration.md when adding/modifying database columns.
This prevents:
User: "I need to add a column to my SwiftData model"
→ Read: skills/database-migration.md (critical - prevents data loss)
User: "How do I query SwiftData with complex filters?"
→ Read: skills/swiftdata.md
User: "CloudKit sync isn't working"
→ Read: skills/cloud-sync-diag.md
User: "Should I use SwiftData or SQLiteData?"
→ Read: skills/sqlitedata-migration.md
User: "Check my Core Data code for safety issues"
→ Launch: core-data-auditor agent
User: "Scan for Codable anti-patterns before release"
→ Launch: codable-auditor agent
User: "Audit my iCloud sync implementation"
→ Launch: icloud-auditor agent
User: "Check if my files are stored in the right locations"
→ Launch: storage-auditor agent
User: "Audit my database migrations for safety"
→ Launch: database-schema-auditor agent
User: "How do I make my GRDB queries faster?"
→ Read: skills/grdb-performance.md
User: "Add search to my GRDB-backed app" / "Add search to SQLiteData app"
→ Read: skills/sqlite-fts-ref.md
User: "My widget needs to read the same database as the app"
→ Read: skills/grdb-app-groups.md
User: "My widget shows stale data from the database"
→ Read: skills/grdb-app-groups.md
User: "Audit my GRDB code for performance issues"
→ Launch: grdb-performance-auditor agent
User: "Check my SwiftData models for issues"
→ Launch: swiftdata-auditor agent
User: "How do I persist data on tvOS?"
→ Invoke: See axiom-swift (skills/tvos.md) + Read: skills/sqlitedata.md
User: "My tvOS app loses data between launches" → Invoke: See axiom-swift (skills/tvos.md)
User: "How do I store an auth token securely?" → Invoke: See axiom-security (skills/keychain.md)
User: "errSecDuplicateItem but I checked and the item doesn't exist" → Invoke: See axiom-security (skills/keychain-diag.md)
User: "How do I encrypt data with AES in Swift?" → Invoke: See axiom-security (skills/cryptokit.md)
User: "I need to sign data with the Secure Enclave" → Invoke: See axiom-security (skills/cryptokit.md)
User: "What's ML-KEM and should I use it?" → Invoke: See axiom-security (skills/cryptokit.md)
Use when the user mentions GRDB performance review, slow GRDB queries, app-group database setup audit, or pre-release GRDB scan.
Use when writing ANY async code, actors, threads, or seeing ANY concurrency error. Covers Swift 6 concurrency, @MainActor, Sendable, data races, async/await patterns.
Use when integrating ANY iOS system feature - Siri, Shortcuts, widgets, IAP, localization, privacy, alarms, calendar, reminders, contacts, background tasks, push notifications, timers. Covers App Intents, WidgetKit, StoreKit, EventKit, Contacts.
Use when app feels slow, memory grows, battery drains, or diagnosing ANY performance issue. Covers memory leaks, profiling, Instruments workflows, retain cycles, performance optimization.
Use when storing credentials securely, encrypting data, implementing passkeys, code signing, or managing certificates and provisioning profiles.
Use when building, fixing, or improving ANY SwiftUI UI — views, navigation, layout, animations, performance, architecture, gestures, debugging, iOS 26 features.