From Apprehension to Adoption — Why .NET Minimal APIs Are Shaping the Future of Backend Development

From Apprehension to Adoption — Why .NET Minimal APIs Are Shaping the Future of Backend Development

Most .NET developers first meet Minimal APIs with mixed feelings:

“They look cool and concise… but can I build a real system like this?”

After years of controllers, attributes, and layered Web API projects, a single Program.cs file full of routes can feel dangerously simple. Where do I put validation? How do I keep things maintainable? What about logging, Swagger, or authentication?

This post is your roadmap from apprehension to adoption:

• We’ll demystify what Minimal APIs actually are.
• We’ll tackle the most common fears (scalability, structure, tooling).
• We’ll build a production‑style Minimal API with:
  • Feature‑based endpoint organization
  • Middleware for cross‑cutting concerns
  • Swagger / OpenAPI
  • Global exception handling
  • JWT authentication & authorization
  • FluentValidation for input validation
  • Endpoint filters for extra cross‑cutting logic

Treat this as both a conceptual guide and a starter blueprint for your next .NET 8/9 backend.

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Table of Contents

1. Why Minimal APIs? The Real Shift Behind the Hype
2. Minimal APIs in 60 Seconds: What They Actually Are
3. The Three Big Apprehensions (and Honest Answers)
4. Structuring a Real‑World Minimal API
5. Middleware: Cross‑Cutting Concerns Without Controllers
6. Swagger / OpenAPI: First‑Class Support, Minimal Ceremony
7. Global Exception Handling with IExceptionHandler
8. Authentication & Authorization with JWT
9. Validation with FluentValidation
10. Endpoint Filters: Intercepting Requests and Responses
11. Migration Strategy: From Controllers to Minimal APIs
12. Conclusion: Minimal APIs as the Default, Not the Experiment

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1. Why Minimal APIs? The Real Shift Behind the Hype

Minimal APIs aren’t just about fewer keystrokes or a trendy syntax.

They represent a shift in how we build HTTP APIs in .NET:

• Less ceremony, more focus on the actual HTTP contract (routes, status codes, responses).
• Less runtime overhead, more performance, especially in high‑traffic or microservice scenarios.
• Fewer framework constructs to learn, lower barrier of entry for new .NET developers.

Key advantages

• Reduced boilerplate — No controllers, no attributes jungle. You define endpoints directly on the WebApplication.
• Better performance — Fewer abstractions in the pipeline can translate into tighter, faster code paths.
• Straightforward onboarding — New developers can read Program.cs and understand how requests are handled.

Minimal APIs are essentially saying:

“Let’s remove everything that doesn’t need to be there… and keep the things that actually matter for HTTP APIs.”

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2. Minimal APIs in 60 Seconds: What They Actually Are

Under the hood, Minimal APIs are just ASP.NET Core.

They use the same hosting model, middleware pipeline, dependency injection container, and configuration system as controllers. The difference is how you define endpoints.

var builder = WebApplication.CreateBuilder(args);
var app = builder.Build();

app.MapGet("/hello", () => "Hello, Minimal APIs 👋");

app.Run();

That’s a complete HTTP API.

Instead of:

• Controller classes
• Routing attributes like [HttpGet("...")]
• Model binding attributes everywhere

…you map routes directly on the WebApplication and let .NET handle the rest.

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3. The Three Big Apprehensions (and Honest Answers)

Let’s address the elephant(s) in the room.

3.1 “I’m afraid of the unknown”

Fair. Controllers have been around for over a decade. Minimal APIs feel new, but they are built on the same ASP.NET Core foundations you already know: middleware, DI, filters, configuration, authentication.

Once you realize that only the routing style changed, the fear drops significantly.

3.2 “Can Minimal APIs scale for large, complex backends?”

Yes — if you structure them well.

A messy Program.cs with 200 endpoints is not a Minimal API problem; it’s an architecture problem.

The fix is the same as in controller projects: structure your code by feature, not by technical layer. We’ll see how in the next section.

3.3 “Is tooling and community support ready?”

Short answer: yes.

• Swagger & OpenAPI? ✅ Supported.
• Authentication & authorization? ✅ Same stack.
• Filters, validation, exception handling? ✅ Supported.
• IDE & debugging support? ✅ Built‑in.

Minimal APIs are not an experiment anymore. They’re a first‑class citizen in modern ASP.NET Core.

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4. Structuring a Real‑World Minimal API

A trivial demo put everything in Program.cs. A real system should not.

A solid pattern is:

src/
  MyApp.Api/
    Endpoints/
      Todo/
        TodoEndpoints.cs
        TodoModules.cs
    Middleware/
      CustomLoggingMiddleware.cs
    Config/
      JwtConfiguration.cs
    Program.cs

Let’s walk through a Todo example using an endpoint group.

4.1 Grouping endpoints with extension methods

Endpoints/Todo/TodoEndpoints.cs:

public static class TodoEndpoints
{
    public static void MapTodoEndpoints(this WebApplication app)
    {
        var todos = app.MapGroup("/todo");

        todos.MapGet("/list", TodoModules.GetTodoList)
             .RequireAuthorization()
             .Produces<TodoDto>(StatusCodes.Status200OK);
    }
}

We get:

• /todo group as a route prefix.
• /todo/list endpoint with:
  • Auth required
  • Strongly typed response advertised via Produces<T>().

4.2 Extracting logic into modules

Endpoints/Todo/TodoModules.cs:

public class TodoModules
{
    public static async Task<IResult> GetTodoList(ITodoRepository todoRepository)
    {
        var items = await todoRepository.GetAllAsync();
        return TypedResults.Ok(items);
    }
}

Key idea: Minimal APIs don’t force you to put logic in lambdas.

You can (and should) move behavior into testable classes and methods.

4.3 Wiring everything in Program.cs

var builder = WebApplication.CreateBuilder(args);

// Register services
builder.Services.AddScoped<ITodoRepository, TodoRepository>();

var app = builder.Build();

// Map feature endpoints
app.MapTodoEndpoints();

app.Run();

Result: you keep minimalism at the edges, structure and testability in your feature modules.

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5. Middleware: Cross‑Cutting Concerns Without Controllers

Need logging, tracing, or custom headers on every request? Use middleware.

Example: a simple request timing logger.

public class CustomLoggingMiddleware
{
    private readonly RequestDelegate _next;

    public CustomLoggingMiddleware(RequestDelegate next)
        => _next = next;

    public async Task InvokeAsync(HttpContext context)
    {
        var started = DateTime.UtcNow;

        try
        {
            await _next(context);
        }
        finally
        {
            var elapsed = DateTime.UtcNow - started;
            Console.WriteLine(
                $"[{context.Request.Method}] {context.Request.Path} " +
                $"=> {context.Response.StatusCode} in {elapsed.TotalMilliseconds} ms");
        }
    }
}

Register it in Program.cs:

app.UseMiddleware<CustomLoggingMiddleware>();

Everything still flows through the same familiar request pipeline as controller‑based apps.

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6. Swagger / OpenAPI: First‑Class Support, Minimal Ceremony

Documentation is not optional. Minimal APIs work perfectly with Swashbuckle.

6.1 Install the package

dotnet add package Swashbuckle.AspNetCore

6.2 Add Swagger in Program.cs

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddEndpointsApiExplorer();
builder.Services.AddSwaggerGen();

var app = builder.Build();

app.MapTodoEndpoints();

if (app.Environment.IsDevelopment())
{
    app.UseSwagger();
    app.UseSwaggerUI(c =>
    {
        c.SwaggerEndpoint("/swagger/v1/swagger.json", "Todo API v1");
    });
}

app.Run();

6.3 Enhancing OpenAPI metadata

todos.MapGet("/list", TodoModules.GetTodoList)
     .WithOpenApi(operation =>
     {
         operation.Summary = "Gets a list of todo items.";
         operation.Description = "Retrieves all todos available for the current user.";
         operation.Tags = new[] { "Todo" };
         return operation;
     })
     .Produces<TodoDto[]>(StatusCodes.Status200OK);

You can deliver a discoverable, self‑documenting API without controllers or attributes.

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7. Global Exception Handling with IExceptionHandler

.NET provides IExceptionHandler to centralize how you deal with unhandled exceptions.

7.1 Implement a global handler

public sealed class GlobalExceptionHandler : IExceptionHandler
{
    public async ValueTask<bool> TryHandleAsync(
        HttpContext httpContext,
        Exception exception,
        CancellationToken cancellationToken)
    {
        // Log exception here (Serilog, Application Insights, etc.)

        var problem = new
        {
            Status = StatusCodes.Status500InternalServerError,
            Title = "An unexpected error occurred.",
            Type = "https://datatracker.ietf.org/doc/html/rfc7231#section-6.6.1"
        };

        httpContext.Response.StatusCode = StatusCodes.Status500InternalServerError;
        await httpContext.Response.WriteAsJsonAsync(problem, cancellationToken);

        return true;
    }
}

7.2 Register the handler

var builder = WebApplication.CreateBuilder(args);

builder.Services
    .AddExceptionHandler<GlobalExceptionHandler>()
    .AddProblemDetails();

var app = builder.Build();

app.UseExceptionHandler();

app.MapTodoEndpoints();

app.Run();

Now, your Minimal API returns consistent, structured error responses without sprinkling try/catch everywhere.

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8. Authentication & Authorization with JWT

Minimal APIs reuse the same authentication and authorization stack as MVC.

8.1 Configure JWT authentication

var builder = WebApplication.CreateBuilder(args);

builder.Services
    .AddAuthentication(options =>
    {
        options.DefaultAuthenticateScheme = JwtBearerDefaults.AuthenticationScheme;
        options.DefaultChallengeScheme = JwtBearerDefaults.AuthenticationScheme;
    })
    .AddJwtBearer(options =>
    {
        options.TokenValidationParameters = new TokenValidationParameters
        {
            ValidIssuer = builder.Configuration["Jwt:Issuer"],
            ValidAudience = builder.Configuration["Jwt:Audience"],
            IssuerSigningKey = new SymmetricSecurityKey(
                Encoding.UTF8.GetBytes(builder.Configuration["Jwt:Key"]!)),
            ValidateIssuer = true,
            ValidateAudience = true,
            ValidateLifetime = true,
            ValidateIssuerSigningKey = true
        };
    });

builder.Services.AddAuthorization();

var app = builder.Build();

app.UseAuthentication();
app.UseAuthorization();

8.2 Protect routes and groups

public static class TodoEndpoints
{
    public static void MapTodoEndpoints(this WebApplication app)
    {
        var todos = app.MapGroup("/todo")
                       .RequireAuthorization(); // All endpoints require auth

        todos.MapGet("/list", TodoModules.GetTodoList)
             .Produces<TodoDto[]>(StatusCodes.Status200OK);

        todos.MapGet("/public-info", () => "Hello, anonymous!")
             .AllowAnonymous();
    }
}

You get fine‑grained control over which endpoints require tokens and which don’t.

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9. Validation with FluentValidation

Model validation in Minimal APIs is just as powerful — you simply wire it up explicitly.

9.1 Define a validator

public sealed class TodoItemValidator : AbstractValidator<TodoItem>
{
    public TodoItemValidator()
    {
        RuleFor(x => x.Title)
            .NotEmpty()
            .MaximumLength(100);

        RuleFor(x => x.Description)
            .MaximumLength(500);

        RuleFor(x => x.IsComplete)
            .NotNull();
    }
}

9.2 Register validators

builder.Services.AddValidatorsFromAssembly(typeof(Program).Assembly);

9.3 Use them in your endpoints or modules

public static class TodoModules
{
    public static async Task<IResult> AddTodo(
        TodoItem todo,
        IValidator<TodoItem> validator,
        ITodoRepository repository)
    {
        var result = await validator.ValidateAsync(todo);
        if (!result.IsValid)
        {
            return Results.BadRequest(result.Errors);
        }

        await repository.AddAsync(todo);
        return Results.Created($"/todo/{todo.Id}", todo);
    }
}

You keep validation explicit, composable, and testable.

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10. Endpoint Filters: Intercepting Requests and Responses

Endpoint filters are like lightweight, per‑endpoint middleware.

10.1 Create a filter

public sealed class LoggerEndpointFilter : IEndpointFilter
{
    private readonly ILogger _logger;

    public LoggerEndpointFilter(ILoggerFactory loggerFactory)
        => _logger = loggerFactory.CreateLogger<LoggerEndpointFilter>();

    public async ValueTask<object?> InvokeAsync(
        EndpointFilterInvocationContext context,
        EndpointFilterDelegate next)
    {
        _logger.LogInformation("Before endpoint execution: {Path}", context.HttpContext.Request.Path);

        var result = await next(context);

        _logger.LogInformation("After endpoint execution: {Path}", context.HttpContext.Request.Path);

        return result;
    }
}

10.2 Apply it to an endpoint

public static class TodoEndpoints
{
    public static void MapTodoEndpoints(this WebApplication app)
    {
        var todos = app.MapGroup("/todo");

        todos.MapGet("/list", TodoModules.GetTodoList)
             .AddEndpointFilter<LoggerEndpointFilter>()
             .Produces<TodoDto[]>(StatusCodes.Status200OK);
    }
}

Use filters for:

• Extra logging or metrics
• Simple caching strategies
• Permission checks before hitting business logic

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11. Migration Strategy: From Controllers to Minimal APIs

You don’t need a big‑bang rewrite.

A pragmatic migration approach:

1. Start with a new module
   
   New feature? Implement it as a Minimal API endpoint group instead of a controller.

2. Extract logic into modules/handlers
   
   Keep your controllers around, but move shared logic into reusable services you can call from both controllers and Minimal APIs.

3. Gradually move routes
   
   For existing controllers, move low‑risk endpoints into Minimal APIs first (health checks, simple reads, internal tools).

4. Align structure by feature
   
   Create Endpoints/<Feature> folders and let them live side‑by‑side with your existing layers until all new work flows via Minimal APIs.

5. Standardize patterns
   
   As your team gets comfortable, standardize on:

   • Endpoint groups per feature
   • Consistent error shape via IExceptionHandler
   • Common OpenAPI conventions
   • Shared abstractions only when truly cross‑cutting

Minimal APIs are fully compatible with MVC controllers, so you can mix & match during the transition.

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12. Conclusion: Minimal APIs as the Default, Not the Experiment

Minimal APIs started as “the new shiny thing” — now they are a serious, production‑ready default for building HTTP backends in .NET.

They give you:

• A lean and expressive way to define endpoints.
• Familiar access to the full ASP.NET Core ecosystem: middleware, DI, logging, auth, Swagger, filters.
• Enough flexibility to organize by feature, not framework.

The apprehension usually comes from one place:

“If I remove controllers, will my architecture collapse?”

The answer is no — if you replace them with clear, feature‑oriented structure:

• Endpoint groups per feature
• Modules/handlers for business logic
• Middleware and filters for cross‑cutting concerns
• Validators for robust boundaries
• Exception handlers for consistent errors

Once your team ships a couple of services with Minimal APIs, they stop feeling like a risk and start feeling like what they really are:

A faster, cleaner way to express your HTTP API in .NET.

Happy coding — and enjoy building your next backend with Minimal APIs. 🚀