Building SaaS Payment Systems with Stripe × Antigravity
Building a SaaS product requires handling complex payment operations, subscription management, and compliance. Antigravity paired with Stripe's payment infrastructure enables rapid, production-ready implementation.
Stripe Integration Architecture
Modern SaaS needs:
- Checkout system: Secure payment collection
- Subscription management: Billing cycles and plan changes
- Webhook handling: Real-time payment event processing
- Tax calculation: Automated tax compliance
- Invoice management: Automatic invoice generation and delivery
- Refund handling: Refund processing and reconciliation
SaaS Pricing Models
Flat-rate Subscription
Single price per month for all users.
Usage-based Billing
Charges based on metrics (API calls, storage, users).
Tiered Pricing
Multiple plan tiers at different price points with feature differences.
Hybrid Model
Base subscription + usage overage charges.
Implementation with Antigravity
Request Antigravity to generate:
- Backend APIs for subscription management
- Webhook handlers for payment events
- Tax calculation services
- Invoice generation systems
The agent generates production-ready code following security best practices.
Webhook Security and Event Processing
Handle Stripe webhooks securely:
- Verify webhook signatures
- Idempotent event processing
- Proper error handling and retries
Antigravity generates webhook handlers with these security patterns.
Subscription Lifecycle Management
Manage customer journeys:
- Signup: Initial subscription creation
- Active: Ongoing subscription
- Past Due: Unpaid invoice
- Canceled: Subscription ended
Handle transitions with proper billing logic.
Refund and Chargeback Handling
Implement:
- Refund request processing
- Refund reason tracking
- Chargeback monitoring
- Fraud detection patterns
Tax Compliance
Use Stripe Tax for:
- Automatic tax calculation
- Tax jurisdiction handling
- Compliance reporting
- Invoice tax display
Testing Payment Flows
Use Stripe's test mode to verify:
- Successful payments
- Failed payment handling
- Refund processing
- Subscription transitions
Antigravity generates comprehensive test suites covering all payment scenarios.
Monitoring and Alerting
Set up monitoring for:
- Failed payment retries
- Webhook delivery failures
- Chargeback rates
- Revenue metrics
Production Deployment
Verify before going live:
- Webhook endpoints configured
- API keys securely stored
- Error handling tested
- Monitoring active
A Note from an Indie Developer
I'm Masaki Hirokawa at Dolice, running mobile apps with 50M+ cumulative downloads as a solo developer since 2014. The patterns described above mirror how I approach AdMob-monetized production workflows: ship the minimal core, watch the dashboards for a week, then expand only what the data justifies.
When building SaaS products with Antigravity, I keep two principles in mind. First, separate the agent loop from the deployment loop — your AI agent generating code is a fundamentally different cadence than your CI/CD pipeline shipping it. Second, treat the Stripe webhook handler as the source of truth, not the Stripe Dashboard. I've seen too many indie projects lose paid users to webhook idempotency bugs that the dashboard couldn't surface.
The full-stack approach below is designed for solo founders or two-person teams. If you're bigger, the same patterns apply, but you'll want to add an additional review checkpoint between agent output and production deploy. Either way, start small, instrument generously, and resist the temptation to skip the staging environment — even when Antigravity makes the entire pipeline feel disposable.
Looking back
Antigravity and Stripe together handle the complex payment infrastructure, letting you focus on building your SaaS's core business value.