What Is an API Integration?
An API integration connects two software systems so they can exchange data — your app calls another service's API to read or write data without building that functionality from scratch.
API stands for Application Programming Interface. An integration means your app uses another service's API to exchange data.
Common SaaS API integrations:
- Stripe — payments, subscriptions, invoicing
- Resend / SendGrid — transactional email
- Twilio — SMS notifications
- Google Calendar / iCal — calendar sync
- Supabase — database, auth, storage
How a REST API integration works:
- Your app sends an HTTP request (GET, POST, PUT, DELETE)
- The external service processes it and returns a response
- Your app reads the response and updates its state
Webhooks (reverse direction): Instead of your app polling, the external service pushes updates to your app when something happens — e.g., Stripe sends a webhook when a payment succeeds.
What integrations actually cost in a build: Each non-trivial API integration (Stripe, email, calendar sync) adds 1–3 days to an MVP scope. Webhook handlers, error handling, and retry logic take longer than the initial connection.