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

Clarify First

Before building the integration, confirm these inputs. If any is unknown or vague, ASK — do not assume:

• Framework — Next.js / Express / Django (the handler and client patterns differ per stack)
• Billing model — flat subscription / metered usage-based / trials + proration (shapes the subscription state machine and code)
• Scope — which piece: Checkout, idempotent webhooks, dunning, or SCA/3D Secure (selects the reference and code generated)

Stop rule: ask only the 2-3 that most change the output. If the user says "just draft it," proceed and list your assumptions at the top of the artifact.

References

Load the reference that matches the task — keep this file lean and pull detail on demand:

• references/payment-flows.md — Stripe client setup, plan config, Checkout sessions, Customer Portal, and SCA/3D Secure. Read when wiring up the client or building the checkout/portal redirects.
• references/subscriptions.md — lifecycle state-machine diagram, upgrade/downgrade/preview/cancel code, usage-based billing, feature gating, and the Prisma schema. Read when modeling subscription state or implementing plan changes.
• references/webhooks.md — the full idempotent webhook handler with signature verification and every event handler. Read when building or auditing the webhook endpoint.
• references/testing-and-troubleshooting.md — Stripe CLI testing, common pitfalls, troubleshooting table, and success criteria. Read when testing locally or diagnosing a billing bug.

Related Skills

Scope & Limitations

This skill covers:

• Stripe Checkout, Subscriptions, and Customer Portal integration for SaaS billing
• Webhook handling with idempotency, signature verification, and retry safety
• Usage-based (metered) billing, proration previews, and plan change workflows
• SCA/3D Secure compliance for European payment regulations (PSD2)

This skill does NOT cover:

• Stripe Connect (marketplace payouts, multi-party payments) -- see platform-specific Stripe Connect documentation
• One-time payment flows without subscriptions (e.g., e-commerce product purchases)
• Tax calculation and remittance (Stripe Tax configuration, VAT/GST filing) -- see ra-qm-team/ compliance skills for regulatory guidance
• Payment fraud detection and dispute management (Stripe Radar rules, chargeback workflows) -- see skill-security-auditor for security review patterns

Integration Points