What should I use for auth and database in a mobile app?

It depends a lot on your app, but here’s a practical default recommendation:

Good default stack for most mobile apps

• Auth: Firebase Authentication or Auth0
• Database: Firebase Firestore if you want fast mobile-friendly development
  or PostgreSQL if you want a more traditional, scalable backend

When to choose what

Use Firebase Auth + Firestore if:

• You want the fastest setup
• Your app is a startup/MVP
• You want built-in mobile SDKs
• You prefer less backend maintenance
• Your data is document-oriented and not heavily relational

Pros

• Very easy to integrate in iOS/Android/Flutter/React Native
• Handles email/password, phone, Google, Apple, etc.
• Firestore sync/offline support is great for mobile
• Minimal backend work

Cons

• Can get expensive at scale
• Complex relational queries are awkward
• Vendor lock-in is higher

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Use Auth0 + PostgreSQL if:

• You want strong auth features and flexibility
• You expect enterprise/login complexity
• You want a “real backend” with relational data
• You care about portability and structure

Pros

• Very robust auth system
• PostgreSQL is excellent for most app data
• Easier to model complex relationships
• Better long-term flexibility

Cons

• More setup and backend work
• You need to build more of the API layer yourself

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Use Supabase if:

• You want a middle ground
• You like PostgreSQL but want Firebase-like developer experience
• You want auth + database + storage in one platform

Pros

• PostgreSQL underneath
• Built-in auth
• Row-level security is powerful
• Good developer experience

Cons

• Less mature than Firebase/Auth0 in some areas
• Some advanced auth scenarios may still need custom work

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Simple rule of thumb

• MVP / small team / speed: Firebase Auth + Firestore
• Structured app / long-term / complex data: Auth0 (or Supabase Auth) + PostgreSQL
• Want best all-around modern choice: Supabase

My recommendation

If you’re building a typical mobile app today, I’d suggest:

• Auth: Supabase Auth or Firebase Auth
• Database: PostgreSQL via Supabase if possible

That gives you:

• mobile-friendly auth
• a solid database
• easier scaling than Firestore for relational data
• less vendor lock-in than a pure Firebase stack

If you want, I can recommend a stack based on your app type:

• social app
• ecommerce
• marketplace
• chat app
• fitness/tracking app
• SaaS/mobile-first product