CloudKit Reference

CloudKit reference for database-backed iCloud storage, sync, and sharing. Covers the three modern sync approaches (SwiftData + CloudKit, CKSyncEngine, raw CloudKit), the two record-sharing models, and conflict resolution.

For file/document iCloud (a ubiquitous container) see icloud-drive-ref — a different problem. For sync failures and conflict debugging, see cloud-sync-diag.

When to Use This Reference

Use this reference when you're:

• Choosing between SwiftData + CloudKit, CKSyncEngine, and raw CloudKit APIs
• Syncing structured records (with relationships) across a user's devices
• Sharing records or an entire zone with other iCloud users (collaboration)
• Deciding between root-record and zone-wide sharing
• Resolving save conflicts (CKError.serverRecordChanged, save policies)
• Setting up custom zones, subscriptions, and change tracking
• Monitoring CloudKit error rates and quota in the Console

Example Prompts

Questions you can ask Claude that will draw from this reference:

• "Should I use SwiftData + CloudKit or CKSyncEngine for my app?"
• "How do I share a record with another iCloud user?"
• "Should I use root-record (CKShare(rootRecord:)) or zone-wide (CKShare(recordZoneID:)) sharing?"
• "I shared my data but the person I invited sees a blank/empty list — why?"
• "How do I share an entire CloudKit zone?"
• "How do I handle CKError.serverRecordChanged conflicts?"
• "How do I fetch only the changes since my last sync?"

What's Covered

Sync Approaches

• SwiftData + CloudKit — ModelConfiguration(cloudKitDatabase:); private-DB only, no @Attribute(.unique)
• CKSyncEngine — automatic fetch/upload for custom persistence (SQLite/GRDB/JSON)
• Raw CloudKit — CKContainer, CKDatabase, CKRecord, CKRecordZone, CKModifyRecordsOperation

Databases & Scopes

• Private / Public / Shared scopes — access, SwiftData support, use case
• privateCloudDatabase, publicCloudDatabase, sharedCloudDatabase

Zones & Change Tracking

• Custom zones vs the default zone; CKRecordZone
• CKFetchDatabaseChangesOperation, CKFetchRecordZoneChangesOperation, server change tokens

Subscriptions

• CKSubscription (query / zone / database), silent push, CKModifySubscriptionsOperation

Sharing

• Root-record (hierarchical) – CKShare(rootRecord:); shares a record plus its parent-linked descendants
• Zone-wide – CKShare(recordZoneID:); shares every record in the zone, for apps that read by enumerating the whole zone
• The decision: an enumerate-the-zone app needs zone-wide, or the invitee sees an empty data set (root-record only shares the rooted hierarchy)
• UICloudSharingController, participant permissions, CKAcceptSharesOperation, the CKRecordNameZoneWideShare constant

Conflict Resolution

• Save policies (.ifServerRecordUnchanged), CKError.serverRecordChanged, server/client record merge

Monitoring

• CloudKit Console — error rate, latency percentiles, quota usage, alerts

Key Patterns

SwiftData + CloudKit (the easy path)

let container = try ModelContainer(
    for: Task.self,
    configurations: ModelConfiguration(
        cloudKitDatabase: .private("iCloud.com.example.app")
    )
)

Choosing a sharing model

// Hierarchical: share one record and its parent-linked children.
let share = CKShare(rootRecord: rootRecord)

// Zone-wide: share the whole zone. Use this when the app reads by
// enumerating the zone rather than walking a root hierarchy — with
// root-record sharing, such an app exposes a blank data set to the invitee.
let zoneShare = CKShare(recordZoneID: customZone.zoneID)

Documentation Scope

This page documents the cloudkit-ref skill — database-backed CloudKit (records, sync, sharing). The comprehensive patterns and code live in the skill, which Claude loads automatically.

• For an automated audit of an existing CloudKit/iCloud integration, run the icloud-auditor
• For file/document iCloud rather than record sync, see icloud-drive-ref

Related

• swiftdata – SwiftData models that sync via ModelConfiguration(cloudKitDatabase:)
• cloud-sync-diag – diagnose sync failures and conflict errors when CloudKit misbehaves
• icloud-drive-ref – file/document iCloud sync, distinct from record sync
• storage – choosing CloudKit vs iCloud Drive vs local storage
• icloud-auditor – automated scan for entitlement, CKError-coverage, and account-change gaps

Resources

Docs: /cloudkit, /cloudkit/ckshare, /cloudkit/cksyncengine, /cloudkit/ckrecordzone