APIs: How systems talk
Understand the controlled doorway one system uses to request data or an action from another.
- 8 minutes
- foundation
- Reviewed 2026-07-16
What is it?
An application programming interface is a published contract. A client sends a request to an endpoint; the service validates it and returns a response with data, a result, or an error.
Why does it matter?
Most modern automation becomes useful when it can work across systems. APIs provide a more stable, controllable connection than copying clicks from a screen.
The mental model
An API is a controlled doorway through which one system asks another system for data or action.
A simple example
A workflow sends an order number to an order endpoint. The service returns the status as structured data, which the workflow uses in its next step.
What it is not
An API is not the same as a website interface. A screen is designed for a person; an API is designed for software and usually exposes only approved operations.
Learn this first
These ideas make the lesson easier to place.
- Applications
- Data
Your first 60 minutes
Use one focused hour to make the idea concrete.
- Open a public API example and identify its base address.
- Find one endpoint, its request method, and required inputs.
- Send one read-only request and inspect the status and response.
Build this first
Create a tiny order-status checker that accepts an ID, calls a sample endpoint, and displays success or a useful error.
When not to use it
Do not build a new API when a secure supported connector already solves the problem, or when a one-time manual exchange is cheaper and safer.
What to learn next
Learn JSON so responses become readable, then authentication so requests can be secured.