OpenAPI

Core Principles

1. Built-in, not Swashbuckle — .NET 10 ships Microsoft.AspNetCore.OpenApi as the official, framework-maintained OpenAPI solution. Swashbuckle was removed from templates in .NET 9 and is no longer recommended.
2. TypedResults drive the schema — TypedResults.Ok<T>() automatically generates correct OpenAPI response schemas. Results.Ok() does not. Always use TypedResults.
3. Transformers over workarounds — Document, operation, and schema transformers compose cleanly. Use them for security schemes, global responses, and schema customization.
4. Metadata on every endpoint — Use .WithName(), .WithSummary(), .WithTags() on every endpoint. This metadata feeds directly into the OpenAPI spec and client generators.

Patterns

Basic Setup

var builder = WebApplication.CreateBuilder(args);
builder.Services.AddOpenApi();

var app = builder.Build();