In IoT, APIs are how everything above the device talks. A platform exposes a REST API to list devices, read their latest readings and send commands; a building system exposes one so a dashboard can pull energy data; a vendor’s cloud exposes one so a customer can integrate the product into their own tools. Device-side, an SDK wraps the API so firmware developers do not handle raw HTTP or MQTT.
A good API is the main defense against vendor lock-in: if your data and commands are reachable through documented interfaces, you can move or combine systems. Versioning, rate limits and authentication scope are the details that decide whether an API is usable at fleet scale.
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