What is the difference between Go's standard library and external libraries for providing common and custom functionality in Go programs?

Go's standard library is a set of packages that are included with every installation of the Go programming language. These packages provide a wide range of functionalities, such as input/output operations, networking, encryption, compression, and much more. They are maintained by the Go core team and follow strict backward compatibility guarantees, which means that programs written using these packages will continue to work with future versions of the Go language.

External libraries, also known as third-party packages, are additional packages that are not part of the standard library but can be downloaded and used in Go programs. These packages provide functionality beyond what is available in the standard library and are maintained by various individuals and organizations. They can be found in the Go module repository or on various code hosting platforms, such as GitHub.

The main difference between the standard library and external libraries is that the standard library is included with every installation of the Go language, whereas external libraries need to be explicitly downloaded and added to a project. Additionally, the standard library is maintained by the Go core team and is subject to strict backward compatibility guarantees, while the quality and maintenance of external libraries may vary.

However, external libraries can be extremely useful in providing specialized functionality that may not be available in the standard library. They can also provide better performance, more features, and a more user-friendly interface compared to the standard library in some cases. Therefore, using external libraries can significantly speed up the development process and improve the quality of Go programs.