Firebase (Apple SDK)

Firebase is Google's third-party SDK, not Apple's — it ships from github.com/firebase/firebase-ios-sdk, carries its own release cadence, and depends on a GoogleService-Info.plist you download from the Firebase Console. The deep API reference — install, configuration, the full Auth flows (email/password, anonymous, Sign in with Apple), Firestore CRUD/queries/listeners/transactions, offline persistence, security rules, and the service/manager patterns — lives in references/guide.md. This file is the decision and discipline layer: read it first, open the guide for specifics.

Dials

Set these explicitly at the start; they change what "correct" means.

1. BACKEND — which Firebase products you pull in as SwiftPM products: auth · firestore (document NoSQL, the default data store) · rtdb (Realtime Database, for low-latency presence/streaming) · storage (Cloud Storage for files) · messaging (FCM push) · analytics · crashlytics. Add only the products you use; each is a separate .product(name:, package: "Firebase").
2. AUTH_PROVIDERS — none · email · anonymous · apple (Sign in with Apple via OAuthProvider.appleCredential, requires nonce) · federated (Google/others). Anonymous-then-link is a common upgrade path.
3. FIRESTORE_CACHE — persistent (default; PersistentCacheSettings(), survives launches, serves reads offline) · memory (MemoryCacheSettings(), cleared on relaunch). Set on Firestore.firestore().settings before the first Firestore call.

When to use

Building or reviewing any code that talks to Firebase from an iOS/Swift app — sign-in, Firestore/RTDB reads and writes, real-time listeners, file uploads, push registration, crash reporting, or analytics. If the app uses a different backend (Supabase, CloudKit, a custom API), use that instead — don't run two backends as competing sources of truth.

Core rules