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Foundatio MediatorBuild Loosely Coupled .NET Apps — Without the Tradeoffs

Easy to maintain, easy to test, and blazingly fast — a convention-based mediator powered by source generators and interceptors

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Loosely Coupled by Default

Every interaction flows through messages, so components never call each other directly. Change, replace, or remove any handler without ripple effects across your codebase.

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Compose with Events

Publish an event and any number of handlers react — without knowing about each other. Add new behavior to your app without modifying existing code.

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Easy to Test

Handlers are plain classes with no framework base types. Unit test them like any other object — no mediator mocking, no DI container, no ceremony.

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No Performance Tax

Source generators and C# interceptors compile your mediator calls into near-direct method calls. You get the architecture benefits without the runtime overhead.

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Convention-Based, Zero Boilerplate

No interfaces, no base classes, no manual registration. Just name your classes and methods following simple conventions — the source generator handles all the wiring.

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Auto-Generated API Endpoints

Full Minimal API endpoints generated from your handlers — routes, methods, parameter binding, OpenAPI metadata, and authorization all inferred automatically.

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Real-Time Streaming

Add Server-Sent Events to your API by returning IAsyncEnumerable<T> from a handler. Real-time push with zero infrastructure plumbing.

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Rich Result Types

Built-in Result<T> for success, validation errors, and failure states — auto-mapped to HTTP status codes on endpoints.

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Full Dependency Injection

Built-in support for Microsoft.Extensions.DependencyInjection with constructor and method injection.

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Middleware Pipeline

Before/After/Finally/Execute hooks with state passing and short-circuiting capabilities.

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Automatic Message Cascading

Return tuples to automatically publish additional messages in sequence — ideal for event-driven workflows.

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Compile-Time Safety & Debugging

Comprehensive diagnostics catch errors early. Short, simple call stacks with minimal indirection make debugging straightforward.

Quick Example

Create a simple handler by following naming conventions:

csharp

public record Ping(string Text);public class PingHandler{    public string Handle(Ping msg) => $"Pong: {msg.Text}";}

csharp

// Program.csservices.AddMediator();// Usagevar reply = await mediator.InvokeAsync<string>(new Ping("Hello"));// Output: "Pong: Hello"

Turn your message handlers into API endpoints automatically:

csharp

app.MapMediatorEndpoints();// That's it — routes, methods, and parameter binding are all generated for you.