Stripe Integration Expert

The agent builds production-grade Stripe integrations for SaaS billing: subscription lifecycle management with trials and proration, idempotent webhook handlers, usage-based metered billing, Checkout sessions, Customer Portal, dunning recovery, and SCA/3D Secure compliance. Provides patterns for Next.js, Express, and Django with emphasis on real-world edge cases.

Core Capabilities

• Checkout & client setup — pinned-version Stripe client, centralized plan config, Checkout sessions with trials, tax collection, and promo codes
• Subscription lifecycle — a state machine covering trialing → active → past_due → canceled, plus upgrades/downgrades with proration previews and reactivation
• Idempotent webhooks — signature verification, event dedup, re-fetch-from-API handlers, and retry-safe processing
• Usage-based billing & gating — metered usage records, feature gating by plan, and grace-period access logic
• Dunning & SCA — payment-failure email sequences and PSD2 / 3D Secure authentication flows
• Local testing — Stripe CLI webhook forwarding, event triggers, and test card matrix

When to Use

• Building SaaS subscription billing from scratch on Next.js, Express, or Django
• Adding plan upgrades/downgrades with correct proration behavior
• Hardening or debugging a webhook endpoint for idempotency and retry safety
• Implementing metered/usage-based billing or feature gating by plan
• Adding dunning recovery or European SCA/3D Secure compliance