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.NET version of Pact. Enables consumer driven contract testing, providing a mock service and DSL for the consumer project, and interaction playback and verification for the service provider project.



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Pact Net

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Fast, easy and reliable testing for your APIs and microservices.

Pact is the de-facto API contract testing tool. Replace expensive and brittle end-to-end integration tests with fast, reliable and easy to debug unit tests.

  • Lightning fast
  • 🎈 Effortless full-stack integration testing - from the front-end to the back-end
  • 🔌 Supports HTTP/REST and event-driven systems
  • 🛠️ Configurable mock server
  • 😌 Powerful matching rules prevents brittle tests
  • 🤝 Integrates with Pact Broker / Pactflow for powerful CI/CD workflows
  • 🔡 Supports 12+ languages

Why use Pact?

Contract testing with Pact lets you:

  • Test locally
  • 🚀 Deploy faster
  • ⬇️ Reduce the lead time for change
  • 💰 Reduce the cost of API integration testing
  • 💥 Prevent breaking changes
  • 🔎 Understand your system usage
  • 📃 Document your APIs for free
  • 🗄 Remove the need for complex data fixtures
  • 🤷‍♂️ Reduce the reliance on complex test environments

Watch our series on the problems with end-to-end integrated tests, and how contract testing can help.



Tutorial (60 minutes)

Learn everything in Pact Net in 60 minutes

Upgrading from PactNet v3.x or earlier to v4.x

Upgrade Guide

Looking for PactNet v3.x? See the release/3.x branch.

Need Help


Via Nuget



In the sections below, we provide a brief sample of the typical flow for Pact testing, written in the XUnit framework. To see the complete example and run it, check out the Samples/ReadMe folder.

Writing a Consumer test

Pact is a consumer-driven contract testing tool, which is a fancy way of saying that the API Consumer writes a test to set out its assumptions and needs of its API Provider(s). By unit testing our API client with Pact, it will produce a contract that we can share to our Provider to confirm these assumptions and prevent breaking changes.

In this example, we are going to be testing our User API client, responsible for communicating with the UserAPI over HTTP. It currently has a single method GetUser(id) that will return a User.

Pact tests have a few key properties. We'll demonstrate a common example using the 3A Arrange/Act/Assert pattern.

public class SomethingApiConsumerTests
    private readonly IPactBuilderV3 pactBuilder;

    public SomethingApiConsumerTests()
        // Use default pact directory ..\..\pacts and default log
        // directory ..\..\logs
        var pact = Pact.V3("Something API Consumer", "Something API", new PactConfig());

        // or specify custom log and pact directories
        pact = Pact.V3("Something API Consumer", "Something API", new PactConfig
            PactDir = $"{Directory.GetParent(Directory.GetCurrentDirectory()).Parent.Parent.Parent.FullName}{Path.DirectorySeparatorChar}pacts"

        // Initialize Rust backend
        this.pactBuilder = pact.WithHttpInteractions();

    public async Task GetSomething_WhenTheTesterSomethingExists_ReturnsTheSomething()
        // Arrange
            .UponReceiving("A GET request to retrieve the something")
                .Given("There is a something with id 'tester'")
                .WithRequest(HttpMethod.Get, "/somethings/tester")
                .WithHeader("Accept", "application/json")
                .WithHeader("Content-Type", "application/json; charset=utf-8")
                    id = "tester",
                    firstName = "Totally",
                    lastName = "Awesome"

        await this.pactBuilder.VerifyAsync(async ctx =>
            // Act
            var client = new SomethingApiClient(ctx.MockServerUri);
            var something = await client.GetSomething("tester");

            // Assert
            Assert.Equal("tester", something.Id);


Verifying a Provider

A provider test takes one or more pact files (contracts) as input, and Pact verifies that your provider adheres to the contract. In the simplest case, you can verify a provider as per below. In SomethingApiFixture, the provider is started. In SomethingApiTests, the fixture is verified against the pact files.

public class SomethingApiFixture : IDisposable
    private readonly IHost server;
    public Uri ServerUri { get; }

    public SomethingApiFixture()
        ServerUri = new Uri("http://localhost:9223");
        server = Host.CreateDefaultBuilder()
                     .ConfigureWebHostDefaults(webBuilder =>

    public void Dispose()

public class SomethingApiTests : IClassFixture<SomethingApiFixture>
    private readonly SomethingApiFixture fixture;
    private readonly ITestOutputHelper output;

    public SomethingApiTests(SomethingApiFixture fixture, ITestOutputHelper output)
        this.fixture = fixture;
        this.output = output;

    public void EnsureSomethingApiHonoursPactWithConsumer()
        // Arrange
        var config = new PactVerifierConfig
            Outputters = new List<IOutput>
                // NOTE: PactNet defaults to a ConsoleOutput, however
                // xUnit 2 does not capture the console output, so this
                // sample creates a custom xUnit outputter. You will
                // have to do the same in xUnit projects.
                new XUnitOutput(output),

        string pactPath = Path.Combine("..",
                                       "Something API Consumer-Something API.json");

        // Act / Assert
        IPactVerifier pactVerifier = new PactVerifier(config);
            .ServiceProvider("Something API", fixture.ServerUri)
            .WithFileSource(new FileInfo(pactPath))
            .WithProviderStateUrl(new Uri(fixture.ServerUri, "/provider-states"))

IMPORTANT: You can't use the Microsoft.AspNetCore.Mvc.Testing library to host your API for provider tests. If your tests are using TestServer or WebApplicationFactory then these are running the API with a special in-memory test server instead of running on a real TCP socket. This means the Rust internals can't call the API and therefore all of your provider tests will fail. You must host the API on a proper TCP socket, e.g. by using the Host method shown in the sample above, so that they can be called from non-.Net code.


Messaging Pacts

For writing messaging pacts instead of requests/response pacts, see the messaging pacts guide.



Operating System

Due to using a shared native library instead of C# for the main Pact logic only certain OSs are supported:

OS Arch Support
Windows x86 No
Windows x64 ✔️ Yes
Linux (libc) ARM No
Linux (libc) x86 No
Linux (libc) x64 ✔️ Yes
Linux (musl) Any No
OSX x64 ✔️ Yes
OSX ARM (M1) ⚠️ Coming Soon

Pact Specification

Version Stable Spec Compatibility Install
4.x Stable 2, 3 See installation
3.x Stable 2


The roadmap for Pact and Pact Net is outlined on our main website.




.NET version of Pact. Enables consumer driven contract testing, providing a mock service and DSL for the consumer project, and interaction playback and verification for the service provider project.








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