API Development & Integrations
REST, GraphQL and third-party integrations
Connecting an existing system to Stripe, Mollie, Google Reserve or your own internal API? I build reliable integrations with correct webhook processing, idempotency and solid error handling.
The problem
Most integration bugs appear in production: webhooks arriving twice, missing signature verification, retries double-recording payments. A 'simple Stripe hookup' is rarely simple in production.
What you get
REST or GraphQL API
Versioned endpoints, OpenAPI or GraphQL schema, rate limiting, authentication via JWT or API keys.
Webhook endpoints
Correct signature verification, idempotency keys, automatic retry on downstream errors, dead-letter queue for unprocessable events.
Third-party integrations
Stripe, Mollie, Google Reserve, WhatsApp Business, Resend, HubSpot, Slack, Zapier - common APIs have ready-to-use patterns.
Error handling + retries
Exponential backoff, circuit breakers and structured logging. All errors traceable to the specific request.
Documentation
Postman collection or OpenAPI spec with examples. External developers can send their first request within 10 minutes.
Tech stack
Process
Integration scope → API contract design → staging integration → testing with sandbox/test keys → production switch → monitoring.
Frequently asked questions
Can you extend existing APIs?
Yes. I often work on existing codebases: first an architecture review (2–4 hours), then a concrete extension or refactoring plan.
GraphQL vs REST?
REST is simpler for public APIs and webhook consumers. GraphQL is more powerful for complex frontends that want lots of data with minimal round-trips. Both possible - pick based on consumer.
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