Built-in OpenAPI support for .NET 10 applications. Covers document generation, transformers, TypedResults metadata, security schemes, XML comments, build-time generation, and multiple document support. No Swashbuckle needed. Load this skill when setting up API documentation, customizing OpenAPI output, adding security schemes to docs, or when the user mentions "OpenAPI", "AddOpenApi", "MapOpenApi", "document transformer", "operation transformer", "schema transformer", "OpenAPI 3.1", "API documentation", "Swashbuckle replacement", "Produces", "WithSummary", "WithDescription", "ProblemDetails", "Kiota", or "client generation".
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.
TypedResults drive the schema — TypedResults.Ok<T>() automatically generates correct OpenAPI response schemas. Results.Ok() does not. Always use TypedResults.
Transformers over workarounds — Document, operation, and schema transformers compose cleanly. Use them for security schemes, global responses, and schema customization.
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();
