Abuse prevention - rate limiting, moderation, bad actors. Use when fighting abuse.
Account security - MFA, sessions, recovery. Use when protecting user accounts.
Admin panel - RBAC, config, admin tools. Use when building admin UI.
Application security - OWASP, validation, secrets. Use when securing the app.
Authentication patterns - sign-in, SSO, passkeys, sessions. Use when implementing auth flows.
Billing - Stripe, webhooks, subscriptions. Use when implementing payments.
Code quality - patterns, testing, maintainability. Use for code review.
Competitive analysis - market research, feature gaps. Use when exploring what competitors do.