What is an interface (API) – explained simply?

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An API works like a menu. It tells you what can be ordered and in what form it will arrive. What happens in the kitchen is none of your concern – and it can change without you noticing.

Without an API, it would be like going into the kitchen yourself and searching the refrigerator. This works until someone remodels the kitchen.

Why This Matters

Direct access to the database of an external system is the most common cause of integrations breaking after an update. An API is a promise: "These fields exist, and they are named this way."

What Constitutes a Robust Interface

• Documentation. What requests are available, what responses come back
• Versioning. Changes must not break existing users
• Access Control. Who is allowed to do what
• Error Handling. What happens if the other party does not respond
• Rate Limiting. Protection against overload

The fourth point is the most commonly forgotten. An interface without retry logic loses data unnoticed.

The Practical Question Before Any Integration

Is there a documented API? If yes, the integration is manageable. If no, file exchange remains – functional but slower, more error-prone, and not in real-time.

This question should be clarified before the effort estimation, not afterward.