.NET Framework

.NET Framework is a software development framework and is the original implementation of .NET. It supports building and running websites, services, desktop apps, and more on Windows.

What is .NET Framework? A software development framework.Microsoft

.NET Framework documentationdocsmsft

Code contracts

Code contracts provide a way to specify preconditions, postconditions, and object invariants in .NET Framework code.

• Preconditions are requirements that must be met when entering a method or property.

• Postconditions describe expectations at the time the method or property code exits.

• Object invariants describe the expected state for a class that is in a good state.

Code contracts aren't supported in .NET 5+ (including .NET Core versions). Consider using Nullable reference types instead.