🔐 Authentication Comparison
Firebase Auth vs Lucia
A detailed comparison to help you choose the right tool for your needs.
Last updated: 2026-02-06
Firebase Auth
Free up to 50k MAU (phone auth: 10k/mo free)
Strengths
- + 50,000 monthly active users free — most solo products never hit that ceiling
- + Google, Apple, GitHub, and 10+ social providers work out of the box
- + Plugs directly into Firestore, Cloud Functions, and other Google Cloud services
Weaknesses
- − Tied to the Google ecosystem — using Firebase Auth without other Firebase services feels awkward
- − Custom UI required — no pre-built login components like Clerk offers
- − Migrating user password hashes out of Firebase is possible but painful
Lucia
Free and open source
Strengths
- + Completely free, no MAU limits, no vendor lock-in — it is just a library
- + Works with any database (Postgres, MySQL, SQLite, MongoDB) and any framework
- + Tiny footprint — no external services, your auth data stays in your own database
Weaknesses
- − You build everything yourself — no pre-built login UI, no hosted dashboard
- − Requires solid understanding of sessions, cookies, and auth security
- − Maintained primarily by one developer — smaller bus factor than corporate-backed tools
The verdict
Which one is right for you?
Choose Firebase Auth if you want
- → 50,000 monthly active users free — most solo products never hit that ceiling
- → Google, Apple, GitHub, and 10+ social providers work out of the box
Choose Lucia if you want
- → Completely free, no MAU limits, no vendor lock-in — it is just a library
- → Works with any database (Postgres, MySQL, SQLite, MongoDB) and any framework
In depth
About each tool
Firebase Auth
Google's authentication service with generous free limits and tight integration across the Firebase ecosystem
Firebase Auth handles email/password, social login, phone auth, and anonymous users with minimal setup. Google gives you 50,000 MAU free for most auth methods, which is five times what Clerk or Auth0 offer. If you are already using Firestore or Cloud Functions, Auth plugs in with a single line of config.
The downside is that Firebase Auth is designed to keep you inside Google’s ecosystem. Using it as a standalone auth service — say, with a Postgres database and a Next.js app on Vercel — is doable but clunky compared to Clerk or Supabase Auth. You also need to build your own login UI, since Firebase only provides a basic drop-in widget (FirebaseUI) that looks dated. For solo founders already committed to Firebase, Auth is the obvious choice. For everyone else, evaluate whether you want that Google dependency.
Lucia
Lightweight open-source auth library that gives you full control over your authentication logic
Lucia is auth stripped down to its essentials. It is a TypeScript library that handles session management and gives you helpers for password hashing, OAuth, and token generation. There is no hosted service, no dashboard, no per-user pricing — just code that runs in your app, storing sessions in whatever database you already use.
This makes Lucia the opposite of Clerk or Auth0. You get maximum control and zero recurring costs, but you write more code. You need to build your own login forms, handle email verification flows, and set up OAuth callbacks yourself. For developers comfortable with auth concepts, Lucia is rewarding — your auth is simple, portable, and costs nothing at any scale. For solo founders who want auth done in an afternoon without thinking about security details, a managed service like Clerk or Firebase Auth is a safer bet.
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