How would you improve the maintainability of a large C# codebase?

Start with clear module boundaries, meaningful naming, consistent coding conventions, and classes with focused responsibilities.

Remove duplicated business logic, separate HTTP and persistence concerns from domain rules, and introduce abstractions where they reduce meaningful coupling. Keep public APIs small and explicit. Use nullable reference types, analyzers, formatting tools, code reviews, and automated tests.

Measure architectural complexity as well. Too many layers, interfaces, patterns, and generic abstractions can make a system harder to understand. Refactoring should reduce cognitive load rather than simply increase the number of classes.

Observability, documentation of important architectural decisions, and a reliable CI pipeline also improve long-term maintainability.