Firebase Auth vs Supabase Auth for Solo Developers

Quick Comparison

Firebase Auth Overview

Firebase Auth is Google's authentication service. It supports email/password, phone verification, anonymous auth, and social providers (Google, Apple, Facebook, GitHub, Twitter). The SDKs handle tokens, refresh, and session persistence automatically. You call a function, and the user is authenticated.

The 50,000 MAU free tier means auth is effectively free for early-stage projects. Firebase Auth integrates deeply with Firestore, where security rules reference request.auth.uid to control access. The mobile SDKs (iOS, Android, Flutter) are excellent and handle platform-specific OAuth flows natively.

I use Firebase Auth for a mobile project. Google Sign-In took minutes to implement with the Flutter SDK. Firestore rules handle authorization. The entire auth-to-database flow required zero custom middleware.

Supabase Auth Overview

Supabase Auth is the authentication layer of the Supabase platform. It supports email/password, magic links, phone auth, and social OAuth. The defining feature is Row Level Security integration, where PostgreSQL policies reference auth.uid() to enforce data access at the database level.

The 50,000 MAU free tier matches Firebase's generosity. User data lives in your PostgreSQL database in the auth schema, which you can query and export. The JavaScript client manages sessions automatically, and the auth UI component library provides pre-built forms.

I use Supabase Auth in a web project where the entire backend is Supabase. Users authenticate, RLS policies activate, and database queries automatically scope to the right user. The integration between auth and database access control is Supabase's strongest feature.

Key Differences

Database model. This is the fundamental difference. Firebase uses Firestore (NoSQL document database). Supabase uses PostgreSQL (relational SQL database). Firebase Auth integrates with Firestore security rules. Supabase Auth integrates with PostgreSQL Row Level Security. If you prefer SQL and relational data, Supabase. If you prefer document-based NoSQL, Firebase.

Data ownership. With Supabase, user data sits in a PostgreSQL database you own. You can query the auth.users table directly, export it, or migrate it. Supabase is also open source, so you can self-host everything. Firebase stores your data on Google's servers. Exporting is possible but manual. Self-hosting is not an option.

Open source. Supabase is fully open source. You can read the code, self-host the entire platform, and contribute fixes. Firebase is closed-source SaaS. If open source matters to you philosophically or practically, Supabase is the only choice here.

Mobile SDKs. Firebase has best-in-class native SDKs for iOS, Android, Flutter, and Unity. The mobile auth experience is polished and handles platform-specific quirks (Apple Sign-In requirements, Google Play Services, etc.). Supabase has JavaScript, Dart, Swift, and Kotlin libraries. They work well, but Firebase's mobile SDKs are more mature.

Anonymous auth. Both support anonymous authentication natively now. Firebase has had it for years, and Supabase shipped signInAnonymously in April 2024. Users get a temporary account that can be linked to a real identity later. On Supabase you convert an anonymous user by calling updateUser to attach an email or phone, or linkIdentity to attach an OAuth provider. This pattern is powerful for mobile apps where you want users to experience the product before signing up. The one caveat on the Supabase side is abuse: because anonymous users are real rows in your Postgres auth.users table, Supabase recommends turning on CAPTCHA or Cloudflare Turnstile so a bot cannot inflate your database and your MAU count.

Magic links. Supabase Auth supports passwordless magic link login out of the box. Send an email with a login link, user clicks it, they're authenticated. Firebase can do this with Email Link Authentication, but the setup is more involved. If passwordless email login matters, Supabase handles it more smoothly.

Ecosystem lock-in. Choosing Firebase Auth usually means choosing the Firebase ecosystem: Firestore, Cloud Functions, Cloud Storage. It all works together but ties you to Google. Choosing Supabase Auth means choosing Supabase, but since it's open source, you can self-host or migrate to plain PostgreSQL. The lock-in risk is lower with Supabase.

By the Numbers (2026)

Here is the verified state of both tools as of 28 May 2026. All figures are sourced at the end.

Latest releases. The unified Firebase web SDK (firebase) is at 12.14.0, published 28 May 2026, and the auth submodule (@firebase/auth) is at 1.13.2. Supabase's JavaScript SDK (@supabase/supabase-js) is at 2.106.2, published 25 May 2026, and its auth client (@supabase/auth-js) tracks the same 2.106.2 version.

Adoption. The firebase package pulls roughly 7.3 million weekly npm downloads, with @firebase/auth at about 8.0 million. Supabase pulls more on raw install volume: @supabase/supabase-js is around 19.9 million weekly downloads, and @supabase/auth-js close behind at about 19.9 million.

Open source footprint. This is where the open-versus-closed split shows up concretely. The Supabase monorepo (supabase/supabase) has about 103,000 GitHub stars, and the standalone auth server (supabase/auth, the Go service formerly named GoTrue) has about 2,400 stars. Firebase's web SDK repo (firebase/firebase-js-sdk) has about 5,100 stars, but the Firebase Auth backend itself is closed Google infrastructure with no public repo. You can read, fork, and self-host the entire Supabase auth server. You cannot do that with Firebase.

Free tier. Both give you 50,000 monthly active users for free, which is the headline parity the verdict rests on. The fine print differs. Firebase's Spark plan covers 50,000 MAU for standard email and social auth but only 50 MAU for enterprise SAML/OIDC. Supabase's Free plan covers 50,000 MAU but pauses projects after a week of inactivity and caps you at two active projects.

Paid pricing. Firebase bills auth overages through Google Cloud Identity Platform on a graduated per-MAU scale once you pass 50,000: $0.0055 per MAU from 50,001 to 100,000, $0.0046 from 100,001 to 1,000,000, $0.0032 from 1,000,001 to 10,000,000, and $0.0025 above that. There is no monthly platform fee for auth alone. Supabase folds auth into its platform plans: the Pro plan is $25 per month and includes 100,000 MAU, then $0.00325 per additional MAU. Enterprise SAML/SSO costs $0.015 per MAU on both platforms after their respective free allotments.

Real Cost at Solo-Dev Scale

The headline "both are free to 50,000 MAU" hides where the bill actually lands, so here is the math at a realistic solo-dev growth point.

Assumptions. Your app has grown to 120,000 monthly active users, all using email and social login (no enterprise SSO, no SMS phone auth). You only care about the auth cost, and for Supabase you are already paying the $25 Pro fee because you use the database anyway.

Firebase Auth. The first 50,000 MAU are free. The next 50,000 (from 50,001 to 100,000) bill at $0.0055 per MAU, which is $275. The final 20,000 (from 100,001 to 120,000) bill at $0.0046 per MAU, which is $92. Total auth cost: about $367 per month, with no separate platform fee for auth.

Supabase Auth. The Pro plan's $25 already includes 100,000 MAU. The extra 20,000 bill at $0.00325 per MAU, which is $65. If you count the auth-attributable share as just the overage, that is $65 per month. Even if you load the entire $25 platform fee onto auth, you land at $90 per month.

At this scale Supabase auth is dramatically cheaper because its per-MAU rate is lower and its included MAU pool is twice Firebase's free tier. The trade-off is the $25 floor. Below roughly 50,000 MAU, both are $0 for auth, and a Firebase-only project with no other paid services has no platform fee at all, whereas using Supabase auth in isolation still nudges you toward the $25 Pro plan once you outgrow the Free plan's two-project and inactivity limits. The crossover favors Firebase only at very small scale or when you genuinely use nothing else in the Supabase stack. As soon as you are running a real PostgreSQL backend and crossing into six figures of MAU, Supabase wins on price by a wide margin.

These are auth-line costs only. Database, storage, bandwidth, Firestore reads, and SMS are separate on both platforms and can dwarf the auth bill, so price the whole stack, not just the login box.

When to Choose Firebase Auth

• You're building a mobile app (Firebase's native SDKs are best-in-class)
• You prefer NoSQL/document databases (Firestore)
• You're already invested in the Google Cloud ecosystem
• You need Firebase-specific features (Analytics, Crashlytics, Remote Config)
• You expect to stay well under 50,000 MAU and want the pure pay-as-you-go model with no $25 platform floor

When to Choose Supabase Auth

• You prefer PostgreSQL and relational databases
• Row Level Security for database-level access control is appealing
• Data ownership and the option to self-host matter
• You want magic link authentication out of the box
• Open source is a priority for your stack decisions

The Verdict

Both Firebase Auth and Supabase Auth are excellent choices for solo developers. They offer identical free tiers (50,000 MAU), simple setup, and deep integration with their respective platforms. The deciding factor isn't the auth layer itself. It's the platform behind it.

If you prefer PostgreSQL, SQL, and relational data modeling, choose Supabase Auth. The RLS integration is powerful, data ownership is real, and the open-source foundation means you're never truly locked in.

If you're building a mobile app or prefer NoSQL, choose Firebase Auth. The native SDKs are more mature, the mobile OAuth flows are more polished, and the Firebase ecosystem (Analytics, Crashlytics, Messaging) adds value beyond just auth.

My recommendation: for web apps, Supabase Auth edges ahead because of PostgreSQL, RLS, and open-source advantages. For mobile apps, Firebase Auth is still the more polished choice. Let your database preference and platform choice guide the auth decision, because these tools are both strong enough that the auth layer won't be the bottleneck.

Sources

All figures verified on 28 May 2026.

• Supabase pricing and MAU overage rates: supabase.com/pricing
• Supabase anonymous sign-ins documentation: supabase.com/docs/guides/auth/auth-anonymous
• Supabase anonymous sign-ins announcement (April 2024): supabase.com/blog/anonymous-sign-ins
• Firebase pricing (Spark and Blaze auth tiers): firebase.google.com/pricing
• Google Cloud Identity Platform graduated per-MAU pricing: cloud.google.com/identity-platform/pricing
• Firebase Authentication overview: firebase.google.com/docs/auth
• Supabase Row Level Security documentation: supabase.com/docs/guides/database/postgres/row-level-security
• GitHub stars, languages: github.com/supabase/supabase, github.com/supabase/auth, github.com/firebase/firebase-js-sdk
• npm versions and weekly download counts: registry.npmjs.org/@supabase/supabase-js, registry.npmjs.org/firebase