Lucia vs Keycloak for Solo Developers

Quick Comparison

Lucia Overview

Lucia is an open-source auth library for JavaScript and TypeScript. It provides session management, token generation, and cookie handling as functions you call from your code. You build the rest: registration forms, login logic, OAuth flows, and authorization rules. Lucia is a library in your codebase, not a separate service.

The approach is minimal by design. Lucia handles the cryptographically sensitive parts and trusts you with the application logic. Your database, your schema, your UI, your rules. No external servers, no dashboards, no APIs to call during authentication.

I used Lucia in a Next.js project where I needed sessions with custom expiry logic and embedded metadata. Because Lucia is just a library, I extended it exactly how I needed. The tradeoff was more code upfront, but the result matched my requirements perfectly.

Keycloak Overview

Keycloak is an enterprise-grade identity and access management server from Red Hat. It runs as a standalone Java application (or Docker container) and provides a full admin console for managing users, roles, clients, identity providers, and authentication flows. It supports OIDC, SAML 2.0, LDAP/AD federation, social login, MFA, and fine-grained authorization.

Keycloak is what large organizations use when they need SSO across multiple applications. You deploy it on your infrastructure, configure realms and clients, and your applications authenticate against Keycloak's endpoints. The admin console is a full web UI for managing everything.

I deployed Keycloak for a project with multiple internal apps that needed unified login. The OIDC integration worked well, and the admin console made user management straightforward. But the initial deployment and configuration consumed an entire weekend.

Key Differences

Scope. Lucia is a library. It manages sessions and gives you tools to build auth. Keycloak is a full identity server. It manages users, sessions, roles, social connections, SSO flows, and provides an admin console. They're solving different problems at different scales.

Deployment complexity. Lucia is an npm package. You install it, import it, use it. Keycloak is a Java application that needs its own server, database, TLS certificates, and configuration. For a solo developer, adding Lucia to your app is trivial. Adding Keycloak means operating another service.

SSO and federation. Keycloak excels at SSO across multiple applications. If you have three apps that need the same login, Keycloak handles that natively. Lucia doesn't do cross-application SSO. It manages sessions for a single application. If SSO is a requirement, Keycloak is the answer.

Resource consumption. Lucia runs as part of your application. It adds negligible overhead. Keycloak is a Java server that needs at minimum 512MB-1GB of RAM, more in production. On a small VPS, Keycloak's memory footprint matters. If you're on a $5/month server, Keycloak might not fit.

Language ecosystem. Lucia is JavaScript/TypeScript only. Keycloak speaks OIDC and SAML, so any application in any language can authenticate against it. If your stack includes Python, Go, Ruby, or Java services alongside JavaScript, Keycloak provides a language-agnostic identity layer. Lucia only works within JS/TS.

Admin interface. Keycloak gives you a full web-based admin console for managing users, resetting passwords, configuring social providers, and monitoring sessions. Lucia has no admin interface. User management is done through your application code or directly in the database.

When to Choose Lucia

• You're building a single JavaScript/TypeScript application
• You want auth as a library in your codebase, not a separate service
• Minimal resource overhead matters (shared hosting, small VPS)
• You need custom session logic that standard tools don't support
• You prefer writing code over configuring admin consoles

When to Choose Keycloak

• You need SSO across multiple applications
• SAML or LDAP/AD integration is required
• You want a full admin console for user management
• Your stack includes non-JavaScript services
• You're comfortable managing an additional server

The Verdict

These tools serve different needs. Lucia is for solo developers building a single JavaScript app who want lightweight, custom auth. Keycloak is for developers who need an identity server that multiple applications authenticate against.

For a typical solo developer building one web app, Lucia is the more appropriate choice. It adds auth to your app without the overhead of running a separate Java server. You get exactly the auth behavior you need without the complexity of enterprise identity management.

Keycloak makes sense when you have multiple applications sharing user identities, or when you need SAML/LDAP for enterprise integrations. But for most solo projects, it's overkill. The deployment and maintenance overhead doesn't justify the features unless you specifically need cross-app SSO.

My recommendation: use Lucia if you're building a single JS/TS app and want custom auth. Use Keycloak if you need SSO across multiple services. For everything in between, consider managed solutions like Clerk or Supabase Auth that give you more features than Lucia with less ops work than Keycloak.