Async

Pass your CancellationToken all the way down

When a caller gives up on a request, your code should stop working on it too. It only takes a parameter, but you have to pass it through every layer.

Do you still need ConfigureAwait(false)?

In ASP.NET Core application code, no. In libraries, yes. Here's why the answer depends on where your code runs.

Stream results with IAsyncEnumerable

Loading 100,000 rows into a list before sending the first one wastes memory and time. IAsyncEnumerable<T> lets you process and return items as they arrive.

Stop using async void and fire-and-forget

async void can crash your process, and _ = Task.Run(...) in a web request quietly loses errors and uses disposed services. Here's what to do instead.

ValueTask: when to use it and when not to

ValueTask<T> can save an allocation on hot paths. It also comes with rules that Task doesn't have, and breaking them causes bugs that are hard to trace.