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

If you don’t know the difference, you probably haven’t understood what API and SDK are.

Story:

Developer A created Software A, and Developer B was working on Software B. One day, Developer B wanted to use part of Software A’s functionality without reading its source code. Developer A suggested packaging the needed functionality into a function that B could place in Software B. This function is the API .

The API was born.

Everyday example: Connecting a computer to a phone with a data cable; the cable’s connector acts as the “API interface”.

What is an SDK?

SDK stands for Software Development Kit. It is a broad term for a collection of documentation, examples, and tools that help develop a certain type of software.

SDKs are created to reduce developers’ workload. For example, a company may sell a data‑analysis SDK so other companies can add that functionality without building it from scratch.

Difference between API and SDK:

Generally, there is no sharp distinction because they are related. An SDK can be seen as a virtual package that contains ready‑made software functionality; it is mostly closed except for a small interface, which is the API.

For instance, when adding a new feature (e.g., automatic backup, data analysis, cloud storage) to an enterprise ERP system, instead of developing it from scratch, one can use an SDK that provides the feature and connect to it via its API.

Case study: A research institute built an information platform but had low‑efficiency manual data upload. By inserting a third‑party platform (Jiadouyun) via its API, data was automatically uploaded and backed up. In this process, Jiadouyun acted as the SDK, and its API enabled integration.

Analogy:

Imagine a sealed drink called “SDK”. A straw named “API” sticks into the drink. Your system is the “XX system”. To drink the SDK’s contents (use its functionality), you must use the API straw to connect your system to the SDK.

Bottom line:

SDK = a package containing the software functionality you want.

API = the only interface on the SDK.