axiom-data
Use when working with ANY data persistence, database, storage, CloudKit, migration, or serialization in an Apple app. Covers SwiftData, Core Data, GRDB, SQLite, Realm, CloudKit sync, file storage, Codable, migrations.
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Install
Works with every agent the skills CLI supports.
npx skills add https://github.com/charleswiltgen/axiom --skill axiom-data- 01
Install
Run the command in your project. The CLI asks which agents to install for.
- 02
Describe the task
Ask your agent for something this skill covers. It loads axiom-data automatically when relevant.
- 03
Review the result
The agent follows the SKILL.md steps, scripts and references bundled with the skill.
SKILL.md
The instructions your agent reads when the skill is triggered.
Data & Persistence
You MUST use this skill for ANY data persistence, database, storage, CloudKit, or serialization work.
<!-- AXIOM_AUDITOR_INLINE_BEGIN — auto-maintained by scripts/build-inlined-auditors.ts; do not hand-edit --><!-- AXIOM_AUDITOR_INLINE_END -->Can't launch Axiom agents? Where this router sends you to an agent, follow its procedure inline. Over MCP,
axiom_get_agentreturns it; elsewhere, read its file below, which needs only file search and read.Available here:
skills/codable-auditor.md,skills/core-data-auditor.md,skills/database-schema-auditor.md,skills/grdb-performance-auditor.md,skills/icloud-auditor.md,skills/storage-auditor.md,skills/swiftdata-auditor.md.For any other agent, over MCP
axiom_get_agentreturns it too; run its xclog, xcsym and xcprof steps with theaxiom_xclog_*,axiom_xcsym_*andaxiom_xcprof_*tools. Elsewhere, search Axiom's skills forskills/<agent>.md; if there is none, do that work yourself with this suite's skills, using any Axiom tool on yourPATH.
When to Use
Use this skill when working with:
- Databases (SwiftData, Core Data, GRDB, SQLiteData)
- Schema migrations
- CloudKit sync
- File storage (iCloud Drive, local storage)
- Data serialization (Codable, JSON)
- Storage strategy decisions
- Keychain / secure credential storage
- Encryption, signing, key management (CryptoKit)
Quick Reference
| Symptom / Task | Reference |
|---|---|
SwiftData @Model, @Query, ModelContext, sectioned queries / ResultsObserver / @Attribute(.codable) / dynamic compound predicates (OS27) | 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, upsert, ValueObservation, DatabaseMigrator, encryption | See skills/grdb.md |
| GRDB performance, indexes, EXPLAIN QUERY PLAN, cursors, observation not firing | See skills/grdb-performance.md |
| Full-text search (FTS5) in GRDB or SQLiteData | See skills/sqlite-fts-ref.md |
| Storing or querying JSON inside a SQLite column (JSON1, JSONB) | See skills/sql-json-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 |
@Shared / @SharedReader, appStorage or fileStorage persistence, custom SharedKey, isLoading / loadError on @FetchAll | See skills/swift-sharing.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 guaranteed-persistent local storage) | See axiom-swift (skills/tvos.md) |
| tvOS + CloudKit SyncEngine | See skills/sqlitedata.md |
Automated Scanning
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, INSERT OR REPLACE misused as upsert, observation on WITHOUT ROWID tables, WITHOUT ROWID upsert bugs)
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)
Decision Tree
- SwiftData? →
skills/swiftdata.md,skills/swiftdata-migration.md - Core Data? →
skills/core-data.md,skills/core-data-diag.md - GRDB? →
skills/grdb.md3a. GRDB perf, slow query, schema design for perf? →skills/grdb-performance.md3b. FTS5 (full-text search, any layer)? →skills/sqlite-fts-ref.md3c. DB shared across app + extension/widget/Live Activity? →skills/grdb-app-groups.md - SQLiteData? →
skills/sqlitedata.md,skills/sqlitedata-ref.md4a.@Shared/@SharedReader, or the loading/error state behind@FetchAll? →skills/swift-sharing.md - ANY schema migration? →
skills/database-migration.md(ALWAYS — prevents data loss) - Realm migration? →
skills/realm-migration-ref.md - SwiftData vs SQLiteData? →
skills/sqlitedata-migration.md - Cloud sync architecture? →
skills/cloud-sync.md - CloudKit? →
skills/cloudkit-ref.md - iCloud Drive? →
skills/icloud-drive-ref.md - Cloud sync errors? →
skills/cloud-sync-diag.md - Codable/JSON serialization? →
skills/codable.md - File storage strategy? →
skills/storage.md,skills/storage-diag.md,skills/storage-management-ref.md - File protection? → See axiom-security (skills/file-protection-ref.md)
- Keychain / storing tokens, passwords, secrets securely? → See axiom-security (skills/keychain.md), See axiom-security (skills/keychain-diag.md), See axiom-security (skills/keychain-ref.md)
- SecItem errors (errSecDuplicateItem, errSecItemNotFound, errSecInteractionNotAllowed)? → See axiom-security (skills/keychain-diag.md)
- Encryption, signing, Secure Enclave, CryptoKit? → See axiom-security (skills/cryptokit.md), See axiom-security (skills/cryptokit-ref.md)
- Quantum-secure cryptography, HPKE, ML-KEM? → See axiom-security (skills/cryptokit.md)
- Want Core Data safety scan? → core-data-auditor (Agent)
- Want Codable anti-pattern scan? → codable-auditor (Agent)
- Want iCloud sync audit? → icloud-auditor (Agent)
- Want storage location audit? → storage-auditor (Agent)
- Want database schema/migration safety scan? → database-schema-auditor (Agent) 23a. Want GRDB performance/app-group scan? → grdb-performance-auditor (Agent)
- Want SwiftData code audit? → swiftdata-auditor (Agent)
- tvOS data persistence? → See axiom-swift (skills/tvos.md) (CRITICAL: every local directory is purgeable between launches, so iCloud is the source of truth) +
skills/sqlitedata.md(CloudKit SyncEngine) - SwiftData @MainActor / background context threading? →
/skill axiom-concurrency - Structured data generation with Foundation Models? →
/skill axiom-ai
Sync patterns
- HealthKit anchored/observer queries as a generalizable change-tracking pattern → See axiom-health (skills/sync-and-background.md)
Anti-Rationalization
| 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 has the safe additive patterns and both migration paths to test. |
| "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. |
| "@Shared is just @AppStorage with extra steps" | Mutation goes through $shared.withLock; the plain setter is deprecated, and below Sharing 2.8 on Swift 6.3 it is a compile error wherever a SwiftUI binding is chained into shared state. swift-sharing has the migration. |
| "I'll use local storage on tvOS" | No local directory on tvOS is guaranteed to survive between launches — the system purges them, Caches first. 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. |
Critical Pattern: Migrations
ALWAYS read skills/database-migration.md when adding/modifying database columns.
This prevents:
- "FOREIGN KEY constraint failed" errors
- "no such column" crashes
- Data loss from unsafe migrations
Example Invocations
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: "How do I persist a setting to UserDefaults and observe it everywhere?"
→ Read: skills/swift-sharing.md
User: "Why is my @FetchAll empty — is it loading or did it fail?"
→ Read: skills/swift-sharing.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)
FAQ
What does the axiom-data skill do?
Use when working with ANY data persistence, database, storage, CloudKit, migration, or serialization in an Apple app. Covers SwiftData, Core Data, GRDB, SQLite, Realm, CloudKit sync, file storage, Codable, migrations.
How do I install axiom-data?
Run npx skills add https://github.com/charleswiltgen/axiom --skill axiom-data in your project. The skills CLI detects the agents you use and copies the skill into the right folder. For Claude Code you can also place the skill folder at ~/.claude/skills/axiom-data/ (personal) or .claude/skills/axiom-data/ (project).
Which AI agents can use axiom-data?
Any agent that supports the open Agent Skills format (a folder with a SKILL.md file), including Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, Windsurf, Cline, OpenCode and more.
Is axiom-data safe to install?
No partner security audit is available yet. Skills can run commands and scripts, so read the SKILL.md and any bundled files before installing.
Who maintains axiom-data?
It is published by charleswiltgen in charleswiltgen/axiom. It has 1,306 recorded installs.
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