Writing Maintainable C#: Practical Patterns I Use Every Day

Most code is read far more often than it is written. These are the everyday habits that keep my .NET projects maintainable as they grow.

Keep methods small and honest

A method should do one thing and its name should say what that is. If you need and in the name, it probably wants to be two methods.

Push logic out of controllers

Controllers should coordinate, not calculate. Keeping business rules in services makes them testable and reusable across web, API, and background jobs.

Fail fast and log with context

Validate inputs at the boundary, throw early, and log enough context to diagnose an issue without a debugger.

public async Task<Result> PlaceOrderAsync(OrderRequest request)
{
    if (request is null) throw new ArgumentNullException(nameof(request));
    // ... one clear responsibility per method
}

• Prefer composition over deep inheritance.
• Make illegal states unrepresentable with types.
• Write the test you'd want when this breaks at 2am.

None of this is clever. That's the point — boring, consistent code is the code you can still change next year.