CloudKit vs RxDB

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.

RxDB is a NoSQL database for JavaScript that runs inside an application and keeps data locally on the client. It supports offline operation, including applications that run entirely without a backend. When synchronization is needed, its Sync Engine connects to backends including RxServer, GraphQL, Firebase, Supabase, MongoDB, NATS, HTTP, CouchDB, WebRTC, Appwrite, Google Drive, and Microsoft OneDrive. Observable queries update as stored data changes. RxDB runs in browsers, mobile apps, desktop applications, and servers, with storage options including LocalStorage, IndexedDB, OPFS, SQLite, Node.js Filesystem, Expo Filesystem, MongoDB, and FoundationDB, among others. Collections use JSON Schema with validation and migration support. An encryption plugin protects locally stored documents with a password in browsers, React Native, and Node.js. The free tier is under Apache 2.0 and allows up to 13 open collections in parallel. Free users get community support through GitHub and Discord; Enterprise includes an SLA with a 24-hour first response. Pro costs $99 a month billed annually, and Pro Plus costs $239 a month billed annually.