What’s the Real Difference Between an API and an SDK? A Simple Guide

People who don't know the difference probably haven't grasped what API and SDK mean.

Developer A creates Software A, and Developer B creates Software B. When B wants to use a part of A without reading all of A's source code, A offers a function that B can integrate—this function is the API.

In this story, the function that Developer A provides is the API.

API is the interface that allows other software to use specific functionality without needing to understand the internal implementation.

Everyday example: connecting a computer to a phone with a data cable; the cable acts as the API interface.

SDK stands for Software Development Kit, a collection of documentation, examples, and tools that help developers build software.

SDKs reduce developers' workload by providing ready-made functionality, which can be purchased or used directly.

Thus, an SDK can be seen as a packaged set of features with a single API exposing its functionality.

Real-world case: The China Railway Bridge Research Institute used the Jiandaoyun platform as an SDK, exposing APIs to automatically upload and back up data from their information system.

Analogy: Think of an SDK as a sealed drink, and the API as the straw that lets you sip the drink; without the API you can't access the SDK's functionality.

In short, SDK = a software package containing desired features; API = the sole interface on that package.