This extension helps to monitor the code complexity. As you type, the method complexity "health" is updated, and the complexity is shown near the method.
This is an open source project - https://github.com/elishalom/netcodemetrics. This is a beta version with partial support. Please updated issues in the project issues tracker: Issues tracker (just upload a code sample).
This extension has an alternative implementation based on Roslyn which is up to date. You are encouraged to download it here