Microsoft Dynamics CRM 2013 Custom Code Validation Tool
Legacy Feature Check Tool
There’s an excellent blog post about these tools with video walkthroughs here.
I’ve spoken with many customers/partners lately about these tools in the context of verifying where they stand for upgradability and creating a remediation plan for any unsupported customizations that might break after upgrading. One of the things I have also been emphasizing is how these tools can continued to be used in your development cycles to run a sanity check scan on new customizations. By introducing this approach into your testing process, you decrease the probability you are implementing unsupported customizations that can break during upgrades.