A guide to adding Better Auth authentication to TypeScript and JavaScript applications, with Next.js-specific setup. Authentication is the process of confirming who a user is and managing their login session.

Use it when adding email or social login, two-factor authentication, passkeys, enterprise single sign-on, organizations, API keys, or subscription billing.

It brings login, identity providers, extra sign-in checks, organization accounts, and session handling into one documented approach. It also explains how to connect authentication to databases and billing systems.

better-auth — Skill for Claude Code and Codex by fusengine: A guide to adding Better Auth authentication to TypeScript…

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods

npx agentmods add skills/fusengine/agents/better-auth

Any agent

npx skills add fusengine/agents --skill better-auth

Clone the repo

git clone --depth 1 https://github.com/fusengine/agents

Made for: Claude Code, Codex.

Or install fuse-nextjs, the plugin that ships this one along with the rest of its 11 skills, 1 agent.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

README.md

[![agentmods](https://agentmods.dev/badge/skills/fusengine/agents/better-auth.svg)](https://agentmods.dev/skills/fusengine/agents/better-auth)

Your own site

<a href="https://agentmods.dev/skills/fusengine/agents/better-auth"><img src="https://agentmods.dev/badge/skills/fusengine/agents/better-auth.svg" alt="Measured on agentmods" height="20"></a>

Per session 32 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 1,897 The whole file, excluding the scripts and references it only reads on demand.

Security scan A 0 findings. Scan, not verified.

Origin original No closer match found in the catalogue.

Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

Model	Per session	Once invoked
Fable 5	$0.00032	$0.01897
Opus 5	$0.00016	$0.00949
Sonnet 5	$0.00006	$0.00379
Haiku 4.5	$0.00003	$0.00190

Measured yesterday against content hash 9265eee11fea, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

better-auth scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured yesterday.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

plugins/nextjs-expert/skills/better-auth/SKILL.md · 132 lines

How it starts

The opening of the file, as written. The whole thing — 132 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Covers the full surface — 40+ OAuth providers (Google, GitHub, Discord, Apple, Microsoft, and more), 20+ plugins (2FA, magic links, passkeys, organizations/multi-tenant, enterprise SSO/SAML, SCIM provisioning, Stripe/Polar billing, JWT/Bearer, API keys), and database adapters (Prisma, Drizzle, MongoDB, raw SQL). Also covers migration paths from Auth.js, Clerk, Auth0, Supabase, and WorkOS. While Better Auth itself is framework-agnostic, this skill's architecture guidance (proxy.ts, App Router API route) is Next.js-specific — for Prisma schema/query details see prisma-7.

Better Auth - Complete Authentication

TypeScript-first authentication library with 40+ OAuth providers and 20+ plugins.

Agent Workflow (MANDATORY)

Before ANY implementation, use TeamCreate to spawn 3 agents:

fuse-ai-pilot:explore-codebase - Analyze existing auth setup and patterns
fuse-ai-pilot:research-expert - Verify latest Better Auth docs via Context7/Exa
mcp__context7__query-docs - Check providers/plugins availability

After implementation, run fuse-ai-pilot:sniper for validation.

Overview

When to Use

Implementing authentication in TypeScript/JavaScript applications
Need OAuth providers (Google, GitHub, Discord, Apple, Microsoft, etc.)
Adding 2FA, magic links, passkeys, or phone authentication
Enterprise SSO with SAML, SCIM provisioning, or organizations
Integrating payments with Stripe or Polar subscriptions
Web3 authentication with Sign-In with Ethereum (SIWE)
Migrating from Auth.js, Clerk, Auth0, Supabase, or WorkOS

Why Better Auth

Feature	Benefit
Framework agnostic	Next.js, SvelteKit, Nuxt, Remix, Astro, Expo, NestJS
Plugin architecture	Add only the features you need (20+ plugins)
Full TypeScript	End-to-end type safety, inference included
Self-hosted	Your data stays on your infrastructure
Database flexible	Prisma, Drizzle, MongoDB, PostgreSQL, MySQL, SQLite
Enterprise ready	SSO, SCIM, organizations, audit logs

Read the full file on GitHub · 132 lines

Files

What ships with it

60 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

yesterday First seen · 132 lines · 32 tokens per session scan A 9265eee11fea

Subscribe to this mod's changes

better-auth is a skill published in the GitHub repository fusengine/agents (25 stars, last pushed 1mo ago), licensed MIT. It adds 32 tokens to every session and 1,897 once invoked, about $0.0002 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-09-03.

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