CloudKit vs Realm

CloudKit is Apple’s service for storing structured app and user data in iCloud and synchronizing it across devices and the web. Data is organized in containers with public, private, and shared databases, and synchronization is bidirectional across iOS, iPadOS, macOS, tvOS, watchOS, visionOS, and web apps. CloudKit supports Swift, Objective-C, and JavaScript. Apple Developer Program membership includes up to 1PB of free storage for each app. CloudKit Console lets developers manage containers and schemas, inspect test data, and review telemetry, logs, and alerts. Fields in private databases can be configured for encryption in storage and while travelling to the application. Public databases use World, Authenticated, and Creator roles. Separate sandbox and production environments are provided; production schemas can only be changed in a forward-compatible manner. Automation supports integration tests from Xcode or a CI system, and CKTool JS can be embedded in developer tools. CloudKit JS adds CloudKit support to web apps. A free plan is listed at free, while pricing is from $99/yr. Incoming traffic is throttled by limits and controls that may change over time.

Realm is an object database for local data persistence in mobile and edge applications. It runs directly on phones, tablets, and wearables, and presents data as objects that developers can query in code without an ORM. The database supports relationships, generics, and vectorization. Its documentation describes apps continuing to work through weak signal, offline periods, or outages. Listed SDKs include Java, Swift, Objective-C, JavaScript, and .NET; the JavaScript implementation supports React Native on iOS and Android, as well as Node.js and Electron on Windows, macOS, and Linux. Realm Swift supports encryption in transit and at rest. Realm Studio can open and edit local and synced Realms and administer Realm Object Server instances. Former Device Sync connected data across users, devices, and a backend in real time, but MongoDB announced deprecation of Device Sync and Realm SDKs in September 2024. Realm is free and open source under Apache License 2.0.