SDK vs Library vs Framework - What’s the Difference?

What’s the Difference Between an SDK and a Framework?

Both terms show up in almost every software project, but they serve very different purposes.

Framework - A Structure That Dictates How You Write Your Code

A Framework is a predefined “skeleton.” It determines how the application is built:

• Where you write code
• How classes are divided
• When your functions get called
• What the program’s logical flow is

A Framework uses an Inversion of Control approach: it’s the one that calls your code - not the other way around.

Examples: React, Django, Angular, FastAPI

A Framework is essentially a system you build on top of.

SDK - A Toolkit for Using an Existing System

An SDK, on the other hand, doesn’t dictate how to build your application. It just provides the tools to talk to another system:

• Ready-made functions
• Convenient wrappers
• Libraries + documentation
• Testing and integration tools

An SDK exists to serve you - not to manage your application.

Examples: AWS SDK, OpenAI SDK, NVIDIA TensorRT SDK, Android SDK

With an SDK: you call the tools → you control the flow.

With a Framework: the framework calls your code → the flow is predetermined.

Library vs SDK - What’s the Difference?

Even though both are “ready-to-use code,” they’re fundamentally different.

Library - A Collection of Functions That Add a Specific Capability

A Library is a collection of functions or classes you can use whenever you want.

It doesn’t define:

• How to write code
• How to structure a project
• How to use it in a specific way

It simply provides specific capabilities.

Examples: NumPy, OpenCV, Requests, Matplotlib

SDK - Library + Infrastructure + Tools + Documentation

An SDK sometimes includes a library, but it’s much bigger:

• Code examples
• Development tools
• Simulators
• Full documentation
• Build components
• Configurations
• Tools for communicating with a complex system
• And sometimes even a small Framework on top of the library

A Library is a single brick. An SDK is an entire building kit.

Summary in Three Sentences

• Library = a collection of functions you can call.
• SDK = everything you need to work with a system - libraries + tools + documentation.
• Framework = a structure that dictates how your application is built and runs.