Route groups, endpoint filters, [FromKeyedServices], built-in OpenAPI.

Minimal APIs in .NET 9 — Typed Results, Filters, OpenAPI

Minimal APIs (introduced in .NET 6, matured in .NET 9) wire HTTP endpoints as lambda functions. TypedResults<T> adds compile-time response type information for OpenAPI. Route groups apply middleware to related endpoints. Endpoint filters implement cross-cutting concerns (validation, auth). .NET 9 replaces Swashbuckle with a built-in OpenAPI document generator. [FromKeyedServices] injects named services directly into endpoints.

Interactive Pipeline Flow

FoundationCore LogicProduction

📂 MapGroup — route prefix + meta

MapGroup("/api/orders") creates a group with shared prefix. Apply .RequireAuthorization(), .WithTags(), .AddEndpointFilter() to all endpoints in one call.

Architecture Diagrams

TypedResults for compile-time OpenAPI schema and typed responses.

Loading diagram...

Key Design Decisions

📦Use TypedResults, not Results

TypedResults.Ok<T> carries compile-time type info picked up by the OpenAPI generator. Results.Ok() returns object — OpenAPI can't inspect it.

🔑[FromKeyedServices] for named DI

Inject a specific named service directly into an endpoint: MapGet("/", ([FromKeyedServices("redis")] ICache cache) => ...). No service locator needed.

📖Replace Swashbuckle with built-in OpenAPI

In .NET 9, call app.MapOpenApi() and add a Scalar UI package. Swashbuckle is no longer the default and has fallen behind.

Discussion