Stack
Firebase Auth
Google's authentication service inside the Firebase backend, with native iOS, Android, and web SDKs for sign-in, account linking, and sessions.
What it actually does
Firebase Auth is the login layer of Google's Firebase mobile and web backend. Its SDKs handle sign-in, anonymous auth, account linking, and session management on iOS, Android, and web, with a 99.95% SLA on the paid Identity Platform tier.
The free tier covers 50,000 monthly active users for email/password and social sign-in with no payment method required. Anonymous auth and account linking are built in and free, which suits mobile apps that let users try before creating an account.
Two traps stand out. SMS phone verification is billed per message even on the free plan, so a bot attack on phone sign-in can generate a surprise bill, and the SAML/OIDC free tier is only 50 MAUs before $0.015 per MAU. Set a budget alert before enabling phone auth.
Firebase Auth vs its main rivals
The tools people actually weigh against Firebase Auth: Supabase Auth, AWS Cognito, Clerk, Auth0. Same criteria for every column, including where Firebase Auth loses.
| Firebase Auth |  Supabase Auth |  AWS Cognito |  Clerk |  Auth0 | |
|---|---|---|---|---|---|
Pricing & access | |||||
| Free tier | Unknown50k MAU | Unknown50k MAU | Unknown10k MAU | Unknown50k MRU | Unknown25k MAU |
| Starting price | Usage | $25/mo | Usage | $25/mo | $35/mo |
| Overage per MAU | $0.0055 | $0.00325 | $0.015 | $0.02 | $0.07 |
Platform | |||||
| Mobile SDKs | YesNative | YesYes | YesAmplify | YesYes | YesYes |
| Bundled backend | YesFirestore etc | YesPostgres | YesAWS | NoNo | NoNo |
| Self-host / data ownership | NoNo | YesYes | NoNo | NoNo | NoNo |
Login methods | |||||
| Anonymous auth | YesFree | YesYes | YesGuest | NoNo | NoNo |
| Phone / SMS auth | YesPer-SMS billed | YesAdd-on | YesYes | YesAdd-on | YesAdd-on |
| Prebuilt hosted UI | NoFirebaseUI only | NoNo | YesHosted UI | YesYes | YesUniversal Login |
| Social login | YesFree | YesFree | YesFree | YesFree | YesFree |
| Enterprise SSO (SAML) | Yes50 MAU free | YesPro | YesYes | YesAdd-on | Yes1 free |
Developer & data | |||||
| REST API & SDKs | Free | Free | Free | Free | Free |
- 50,000 free MAUs and the cheapest hosted overage after Supabase at $0.0055 per MAU
- Native SDKs for iOS, Android, and React Native/Expo with a 99.95% paid SLA
- Anonymous auth and account linking are built in and free
- SMS phone verification is billed per message even on the free plan, so bot attacks can spike costs
- SAML/OIDC free tier is only 50 MAUs, then $0.015 per MAU via Identity Platform
- No hosted user store you can self-host; users live in Google's platform
Pay less for it
5 ways foundEmail/password and social sign-in are free for the first 50,000 monthly active users.
Use email and social login instead of SMS to dodge per-message charges and bot-attack bills.
New Google Cloud accounts get $300 in free credits that offset early Identity Platform usage.
Eligible startups receive Google Cloud credits that cover Firebase and Identity Platform spend.
Supabase Auth — For web apps, a lower overage ($0.00325 vs $0.0055) and no per-SMS trap, while still bundling a database.
StackTracker tracks what you actually pay for Firebase Auth and every other tool, flags overpayment, and shows the dollars you would save by switching.
Is it the right tool for you
- You are building a mobile-first iOS or Android app that wants native SDKs
- You want free, reliable auth up to 50k users without enterprise SSO
- You use anonymous auth so users can try the app before signing up
- You rely on phone sign-in and want to avoid per-SMS billing surprises → use Supabase Auth
- You need real enterprise SSO beyond a 50-MAU free cap → use WorkOS or Auth0
Track what Firebase Auth and the rest of your stack cost
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Prices and limits last verified 2026-07-20.