What criteria indicate that your code has good scalability and maintainability?

Good scalability and maintainability of Go code can be determined by several criteria:

• Clean and understandable project structure, separation into packages with clear responsibilities.
• Use of interfaces for abstraction and ease of testing.
• Minimization of code duplication and adherence to DRY principles.
• Well-covered code with tests, which facilitates making changes.
• Use of idiomatic Go code and standard libraries.

For example, if adding new functionality does not require rewriting existing code but simply extending it, then the code is scalable and maintainable.