Choosing Between Minimal APIs and Controllers in .NET 6+

The Boilerplate Burden

Starting a new microservice in .NET often begins with a paradox: you want a simple endpoint to return a piece of data, but the framework asks you to create a Controller class, inherit from ControllerBase, decorate methods with [HttpGet], and manage a separate folder structure before you write a single line of business logic.

The takeaway is simple: if your service is a collection of a few discrete endpoints, Minimal APIs eliminate this ceremony. They allow you to map routes directly in Program.cs, reducing the cognitive load and the number of files required to get a service into production.

How Minimal APIs Shift the Architecture

Minimal APIs move the routing definition from a class-based attribute system to a functional mapping system. Instead of the framework scanning assemblies for controller classes at startup, you explicitly define the relationship between a URL path and a handler (a lambda expression or a method group).

Despite the "minimal" name, these are not stripped-down versions of ASP.NET Core. They use the same middleware pipeline, the same dependency injection (DI) container, and the same routing engine as traditional MVC controllers. The primary difference is the developer experience and a slight reduction in startup overhead due to the lack of controller discovery.

Implementing a Service with Dependency Injection

A common concern is that moving logic to Program.cs leads to a "God File" where everything is tangled. To avoid this, you can inject services directly into the handler parameters. The framework resolves these dependencies from the DI container at the moment the request is handled.

Run the following command in your terminal to create a minimal project:

dotnet new webapi -minimal -o MinimalService

Below is a configuration for a simple product lookup service. This example assumes you are using .NET 6 or later.

// Program.cs
var builder = WebApplication.CreateBuilder(args);

// Register a service in the DI container
builder.Services.AddSingleton<IProductRepository, ProductRepository>();

var app = builder.Build();

// Map a route using a lambda expression
// IProductRepository is injected directly into the handler
app.MapGet("/products/{id}", (int id, IProductRepository repo) =>
{
    var product = repo.GetById(id);
    return product is not null
        ? Results.Ok(product)
        : Results.NotFound();
});

app.Run();

Execution and Verification:

• Permissions: Standard user permissions for the .NET SDK.
• Command: Run dotnet run from the project directory.
• Check: Use curl http://localhost:5000/products/1. If the ID exists in your repository, you should receive a 200 OK with a JSON body.

The Trade-off: Organization vs. Velocity

Minimal APIs are not a total replacement for Controllers; they are a tool for specific scales. As an application grows to dozens of endpoints, the lack of inherent grouping can become a liability.

Feature	Minimal APIs	Controllers (MVC)
Setup Speed	Very High	Moderate
Structure	Flat / Explicit	Hierarchical / Attribute-based
Validation	Manual or via Filter libraries	Built-in Model State validation
Complexity	Low (Ideal for Microservices)	High (Ideal for Monoliths)

One significant limitation is Model Validation. In Controllers, ModelState.IsValid provides an automatic way to handle bad requests. In Minimal APIs, you must either validate the object manually inside the handler or integrate a third-party library like FluentValidation to achieve the same result.

Making the Decision

Choose Minimal APIs when building microservices, serverless functions, or prototypes where the primary goal is low latency and minimal boilerplate. If your project requires complex API versioning, heavy use of OData, or a large team that relies on the strict folder conventions of MVC to navigate the codebase, stick with Controllers.

To verify if your project is truly "minimal", you can inspect the generated assembly or use a profiler to confirm that the Microsoft.AspNetCore.Mvc.Controllers discovery logic is not being executed during the startup sequence.