(This is a subset of Pathoschild.DesignByContract that contains the annotations but does not enforce them.) A high-performance aspect-oriented argument validation framework built on top of the free edition of PostSharp which enables design-by-contract preconditions and postconditions. By annotating your code with attributes like [NotNull], you can eliminate boilerplate validation logic while enabling helpful exception messages and making your code much more robust and refactor-safe. These annotation attributes are also recognized by ReSharper when it has an equivalent annotation, which gives you real-time feedback on contract violations as you type.