SDK (Software Development Kit) and Library are both tools for software development, but they have key differences in concept, purpose, and usage:

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### 1. Definition and Concept
- Library:
A collection of functions, code, or classes that are used to solve specific problems or add specific features to an application. Libraries allow a programmer to use ready-made code instead of writing code from scratch.

Example:
- math in Python for mathematical calculations.
- fmt in Go for formatting and printing.

- SDK:
A more complete set of tools, including libraries, documentation, debugging tools, emulators, and APIs designed to develop software for a specific platform or use a specific service.

Example:
- Android SDK for developing Android applications.
- AWS SDK for working with Amazon services.

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### 2. Main Purpose
- Library:
Perform a specific task or set of tasks (such as reading/writing files, doing math, or connecting to a database).

- SDK:
Provide a complete environment for building an application or system, usually including additional libraries and tools.

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### 3. Usage Level
- Library:
Focuses on a specific problem and is added and called by the programmer in their code.

- SDK:
Provides everything you need to develop an application, including tools, code samples, and even simulators.

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