Async validation lands in Minimal APIs with .NET 11 Preview 6
Preview 6 adds AsyncValidationAttribute and IAsyncValidatableObject so DataAnnotations rules can hit the database before your endpoint runs, without blocking a thread.
Tag: minimal-apis
10 posts
How to return a typed Results<T1, T2> union from a minimal API endpoint in ASP.NET Core 11
Declare the handler's return type as Results<Ok<T>, NotFound> and return TypedResults.Ok / TypedResults.NotFound: the union gives compile-time checking that the handler only returns what it declares, and it self-describes to OpenAPI so you never write .Produces by hand. Covers async handlers, the six-type limit, and testing in ASP.NET Core 11.
Migrate a minimal API from manual validation checks to built-in validation in ASP.NET Core 11
A step-by-step migration guide for replacing hand-rolled if-checks in ASP.NET Core 11 minimal API handlers with the built-in source-generated DataAnnotations validator: what breaks, which manual rules do and do not port, and how to verify the 400 ProblemDetails contract stays identical.
Fix: "415 Unsupported Media Type" from a minimal API endpoint in ASP.NET Core 11
A minimal API returns 415 when the request Content-Type does not match what the endpoint binds. Send Content-Type: application/json for a body-bound type, or use [FromForm] for form and file uploads.
How to customize minimal API validation error responses with IProblemDetailsService in ASP.NET Core 11
Call AddProblemDetails with a CustomizeProblemDetails callback to reshape the 400 that built-in minimal API validation returns in ASP.NET Core 11: add a traceId, rewrite the title, switch 400 to 422, or take full control with a custom IProblemDetailsWriter.
Minimal API validation vs FluentValidation in ASP.NET Core 11: which should you pick?
Use the built-in source-generated validation for synchronous, attribute-expressible rules in ASP.NET Core 11; reach for FluentValidation when you need async rules, complex cross-field logic, or validation kept out of your domain models.
How to organize minimal API endpoints with MapGroup in ASP.NET Core 11
A complete guide to structuring minimal APIs in ASP.NET Core 11 with MapGroup: per-resource endpoint modules as extension methods, nested groups, shared filters and auth, route-parameter prefixes, OpenAPI tags, and the filter-ordering rules that surprise people.
How to validate request bodies in minimal APIs without controllers in ASP.NET Core 11
ASP.NET Core 11 has built-in validation for minimal APIs: call AddValidation, annotate your request record with DataAnnotations, and a source generator validates the bound model and returns 400 ProblemDetails before your handler runs. No controllers, no FluentValidation, no manual checks.
ASP.NET Core in .NET 11 Preview 4 Teaches OpenAPI About the HTTP QUERY Method
.NET 11 Preview 4 makes ASP.NET Core OpenAPI generation recognize HTTP QUERY as a first-class operation in OpenAPI 3.2, with a graceful fallback for 3.0 and 3.1 documents.
Minimal APIs vs controllers in ASP.NET Core 11: which should you pick in 2026?
Pick minimal APIs by default in ASP.NET Core 11. Use controllers only when you need MVC features that minimal APIs still do not match: convention-based routing across many actions, MVC-style filters, or Razor views.