Almost every growing business runs into it at some point: multiple systems that don't communicate with each other. Accounting is in Xero, the CRM is in HubSpot, planning is in a custom tool and reports are manually built in Excel. Every week, all over again.
This is solvable. API integration connects those systems so data flows automatically and manual copy-pasting becomes a thing of the past.
What is an API, exactly?
An API (Application Programming Interface) is a standardized way for software systems to communicate with each other. Almost every modern software application has an API — from Xero and HubSpot to Shopify and SAP.
Simply put: an API is a door through which systems can exchange data. My job is building the connection between those doors.
When is API integration the solution?
API integration is relevant when you:
- Manually transfer data between systems (copy, paste, export/import)
- Build reports by combining data from multiple sources
- Want to connect a new system to existing software
- Need real-time data exchange (e.g., inventory, orders, customer data)
- Want to automate notifications or actions based on events in another system
How does an API integration project work?
A typical integration project follows these steps:
- Mapping — Which data needs to go from which system to which system? What are the fields, formats and frequencies?
- API documentation analysis — Every system has its own rules. Some APIs are excellently documented (Stripe, Twilio), others are a challenge (older enterprise systems).
- Authentication setup — OAuth, API keys, webhooks — the connection must be secure.
- Transformation logic — Data in system A looks different than in system B. Translating that is the real work.
- Error handling — What happens when a system goes offline briefly? Good integrations are resilient to outages.
- Monitoring — After delivery you want to know if the integration is working. Logging and alerts are a standard part of my deliveries.
Real-world examples
Siemens BuildingX Connector
For Siemens I built a production-ready Mendix connector for the BuildingX IoT platform. This involved complex Java implementation, layered REST API integrations and a complete sample application for enterprise customers.
Invoicing automation
An accounting firm manually processed timesheets from dozens of freelancers. We built an automation tool that handles the entire process — from CSV upload to sent PDF invoice — without any manual step.
What does an API integration cost?
Depending on complexity:
- Simple connection between two modern systems: €2,500 – €8,000
- Multi-system integration with transformation logic: €8,000 – €25,000
- Enterprise integration with legacy systems: €25,000+
Timeline is typically 2–8 weeks, depending on the quality of the API documentation and complexity of the business logic.
What makes a good integration?
Many integration projects are built as a "quick fix" — and that comes back to haunt you. A good integration is:
- Reliable: works even when a system is temporarily unreachable
- Documented: so you know exactly what's happening
- Maintainable: when a system changes its API, the adjustment is minimal
- Monitored: alerts when something goes wrong
Ready to get started?
Describe which systems you want to connect and what the data flow should be, and I'll take a free look at whether and how this is technically feasible. See our API integration service for more details.