Better Auth

Overview

Use this skill to deliver production-grade Better Auth setup, migration, and debugging with explicit workflow gates.

Keep this file procedural. Load details from references/playbooks/ first, then exact upstream docs in references/upstream/.

Required Workflow

1. Scan project context before implementation.
2. Capture requirements and decide path.
3. Route to the smallest playbook/reference set.
4. Apply minimum changes.
5. Validate auth flows and safety checks.

Do not skip project scan or requirement intake.

Phase 1: Project Scan and Requirement Intake

Before writing code, confirm:

• Framework/runtime: Next.js, SvelteKit, Nuxt, Express, Hono, etc.
• Database and adapter stack: Prisma, Drizzle, direct driver, MongoDB.
• Existing auth system and migration status.
• Required sign-in methods (email/password, social OAuth, magic link, passkey, phone).
• Required plugins (2FA, organization, bearer/API key, SSO/OIDC/OAuth provider, etc.).
• Email delivery strategy for verification/reset/invitations.
• Security constraints (trusted origins, session policy, CSRF, rate limits).

If any of these are unknown, ask before implementation.

Phase 2: Route to the Right Branch

Branch A: Core Setup / Migration

Use when creating first Better Auth integration or migrating from another provider.

Load in order:

1. references/playbooks/core-setup-migration.md
2. Relevant migration guide in references/upstream/better-auth/llms.txt/docs/guides/
3. Framework integration doc in references/upstream/better-auth/llms.txt/docs/integrations/
4. Adapter doc in references/upstream/better-auth/llms.txt/docs/adapters/

Branch B: Security Hardening

Use when auditing security or fixing trust/session/rate-limit weaknesses.

Load in order:

1. references/playbooks/security-baseline.md
2. references/upstream/better-auth/llms.txt/docs/reference/security.md
3. references/upstream/better-auth/llms.txt/docs/reference/options.md

Branch C: Email/Password Flows

Use for signup/signin/reset/verification/password policy behavior.

Load:

1. references/playbooks/email-password.md
2. references/upstream/better-auth/llms.txt/docs/authentication/email-password.md
3. Relevant plugin docs (email-otp, magic-link, etc.) if used.

Branch D: Organization and Multi-Tenant Flows

Use for org lifecycle, membership, invitations, role/permission patterns.

Load:

1. references/playbooks/organization.md
2. references/upstream/better-auth/llms.txt/docs/plugins/organization.md

Branch E: Two-Factor Flows

Use for TOTP/OTP, backup codes, trusted devices, and 2FA onboarding.

Load:

1. references/playbooks/two-factor.md
2. references/upstream/better-auth/llms.txt/docs/plugins/2fa.md

Branch F: Providers and Error Diagnosis

Use for OAuth/provider setup and explicit error troubleshooting.

Load:

1. references/playbooks/providers-and-errors.md
2. references/error-map.md
3. Exact error docs in references/upstream/better-auth/llms.txt/docs/reference/errors/

Guardrails

• Re-run Better Auth CLI schema generation/migrations after adding or changing plugins.
• Verify env vars and callback/trusted-origin config before concluding root cause.
• Keep fixes scoped to the failing flow; avoid unrelated refactors.
• Use model names (adapter/ORM semantics), not raw table names, when required by adapter config.
• Prefer dedicated plugin import paths over broad plugin imports.

Validation Checklist

For any meaningful auth change:

1. Positive path works (signup/signin/session/use case success).
2. Negative path is handled (invalid credentials/token/provider mismatch).
3. Session behavior is correct (creation, refresh, revocation/log out).
4. Security policy is enforced (origins/rate limits/verification where configured).
5. Schema state is synchronized after plugin changes.

Refresh Upstream Docs

python3 better-auth/scripts/fetch_better_auth_llms.py

Useful modes:

python3 better-auth/scripts/fetch_better_auth_llms.py --dry-run
python3 better-auth/scripts/fetch_better_auth_llms.py --prune

Resource Map

• Playbook index: references/index.md
• Error triage map: references/error-map.md
• Merged playbooks: references/playbooks/
• Upstream corpus: references/upstream/better-auth/
• Refresh script: scripts/fetch_better_auth_llms.py