From Layers to Slices: How I Ship Faster ASP.NET Core APIs
Your API should feel like a collection of small, focused stories, not a scavenger hunt through Services and Interfaces. This tutorial shows how to build a feature first Vertical Slice Architecture in ASP.NET Core using Minimal APIs, MediatR, and FluentValidation. You will see how commands and queries stay tidy, how validation runs before handlers, and how the folder structure reduces friction as your API count grows.
Ever crack open a legacy API and feel like you are rummaging through the kitchen junk drawer looking for scissors? That Services folder keeps getting taller. The Interfaces folder has opinions. And adding a small endpoint kicks off a tab-switching marathon that would make even Dwight Schrute schedule a performance review. There is a simpler way to build APIs that scale without the yak shave. Say hello to vertical slices.
What is a vertical slice
Vertical Slice Architecture organizes code by feature, not by technical layer. Instead of spreading an endpoint across Controllers, Services, Validators, DTOs, and Repositories, you keep everything a feature needs in one place. Think of each slice as a self contained unit that can be developed, tested, and deployed with minimal fuss.
- Feature first: endpoints, handlers, DTOs, validators, and behaviors live together.
- CQRS friendly: commands and queries are different shapes and can evolve independently.
- Clean boundaries: fewer cross project changes when a feature changes.
I still like Clean Architecture for larger systems and domain heavy work. But when your API count grows, feature first slices reduce friction and make onboarding friendlier.
This article will be available on May 11, 2026 at 8 AM Central Time US