Top 20 NuGet contracts Packages

Code Contracts and common functionalities used by other PostSharp pattern libraries. An official PostSharp pattern library.
A simple library that facilitates runtime checks of code and allows to define preconditions and invariants within a method.
Contains contract tests for Rebus services - valuable, if you e.g. want to implement your own Rebus transport, subscription storage, etc.
Argument validation made simple and unified. It ensures arguments conforms to simple validation rules and provides an uniformed exception throwing strategy if arguments are invalid.
Shared contracts (models).
Implements the XMPP IoT legal identities, smart contracts and signatures extesion as defined by the IEEE XMPP IoT Interface working group.
Library for generating typescript contracts from existing CSharp code.
This Guards project is a light-weight toolbox which helps you to protect your public interfaces against invalid parameters being passed over.
Simple Guard (or DbC) implementation.
Contains the core infrastructure contracts for MicroBus which includes the handler and main MicroBus interfaces
Contains the core message contracts for MicroBus which includes the command, query and event interfaces
Deep fork of the Seterlund.CodeGuard library. Example: Guard.That(arg1).IsNotNull().GreaterThan(100); Throws an exception if conditions are not met.
Argument validation methods, for example: this.user = Argument.NotNull("user", user). Less fancy than approaches based on lambdas/anonymous classes, but less scary performance-wise (given that argument checks are often all over the place). Annotations: C# 8 nullable reference types, ReSharper, Mic...
DomainWorkflows dynamic event-driven contracts genaration
Allows use of Defender's Guards through PostSharp aspects.
Gigya ServiceContract
Package Description
Provides static classes for representing program contracts as preconditions in a way that's compatible with System.Diagnostics.Contracts.
Contracts for Storm Connect.
Contracts used with Storm ExportFeedService