How to Build Minimal APIs from Scratch in .NET Core

You can make minimal APIs from scratch in .NET Core. You use simple code and smart design choices. Minimal APIs give you an easy way to build fast web services. They use less memory and work about 40% faster than regular APIs. If you know the framework basics, you can use features like dependency injection and routing. These help you build APIs that are strong and can grow. Good design choices, like thinking about user experience, security, and future needs, help you make APIs that are easy to fix and add to.

Key Takeaways

• Minimal APIs help you build web services with less code. This makes them faster and easier to use.

• Pick the best tools and editors for your work. This helps you code faster and keeps your project neat.

• Use dependency injection to handle your services. This makes your APIs flexible and simple to test.

• Keep your code tidy by grouping similar endpoints together. Use handler classes to make your code easy to read and fix.

• Add error handling and Swagger documentation to your project. This helps users and makes API testing easier.

Setup

Tools Needed

You need some important tools before you start. These tools help you write and test your code. You will use them for your whole project.

• A computer with Windows, macOS, or Linux

• The latest .NET SDK

• A code editor or IDE

• Command-line tools (like Terminal or Command Prompt)

• Internet connection for downloading packages

The Program.cs file is very important in your project. You use it to set up services and endpoints. It also helps you keep your API organized. Good tools help you keep things neat and make work easier. Picking the right tools helps your team work well together and makes things less confusing.

Tip: Tools that support dependency injection and clear routing help you keep your API easy to fix.

Install .NET SDK

You need the .NET SDK to build and run minimal APIs. The SDK gives you what you need to make, build, and test your projects.

1. Go to the official .NET download page.

2. Pick the newest version for your computer.

3. Download and install the SDK by following the steps on the website.

4. Open your terminal or command prompt.

5. Type dotnet --version to see if it worked.

The SDK lets you use features like dependency injection and routing. It also helps you set up Swagger for API documentation, which makes things easier to use and understand.

Editor Setup

Choosing the right editor makes coding easier and faster. Here are some good editors:

• Visual Studio Code (VS Code): Light and has many helpful add-ons for API work, like REST Client and Swagger Viewer.

• JetBrains Rider: Fast and strong, with built-in code checks and version control.

• Visual Studio: Full IDE with great debugging and Git support.

These editors help you keep your code and files organized. They also have features that make building minimal APIs easier. Using a good editor helps you avoid problems, like messy endpoints and hard-to-manage dependencies.

Minimal APIs Basics

What Are Minimal APIs

Minimal APIs help you make web services with less code. You do not need controllers or lots of setup. You put endpoints right in your main file, like Program.cs. This way, you focus on what your API does. You use simple code to handle requests and send back answers.

Minimal APIs use important ideas like keeping client and server separate, stateless requests, and a clear interface. These ideas help you keep your code neat and easy to work with.

You can use patterns like the repository pattern and service layer pattern. These patterns help you keep your code organized. They also make testing and fixing your code easier.

Why Choose Minimal APIs

Pick minimal APIs if you want things fast and simple. They are great for small projects, microservices, and quick tests. You spend less time setting up and more time making features.

• Minimal APIs cut out extra code, so you write only what you need.

• You set up routes directly, which makes them easy to read and fix.

• Testing is easier because your endpoints stay simple.

• You can group code by features, so related parts stay together.

Here is a table that shows why minimal APIs help you build faster:

Key Features

.NET 6 and newer versions make minimal APIs even better. You get new tools that help you build APIs fast.

• You make HTTP endpoints with very little setup.

• You do not need controllers, routing files, or extra middleware.

• You get a lighter choice than MVC, which makes things run faster.

• You can use native AOT compilation for quicker startup.

• You use validation and model binding only when you want them.

Minimal APIs give you an easy way to make web services that are fast, simple to test, and simple to fix.

Build Minimal APIs

Create Project

You can start making minimal APIs by starting a new ASP.NET Core project. Here are the steps to set up your project: First, open your terminal or command prompt. Next, type dotnet new web -n MinimalApiDemo to make a new web project. Then, go to your project folder by typing cd MinimalApiDemo. Open the Program.cs file. This file will have your main code. Now, set up your web app:

var builder = WebApplication.CreateBuilder(args);
var app = builder.Build();
app.MapGet("/", () => "Hello World!");
app.Run();

If you need a database, add extra packages. Type dotnet add package Microsoft.EntityFrameworkCore.InMemory for an in-memory database. Make a model class called WorkItem in a new file named WorkItemApi.cs. Next, create a database context class called WorkItemDb in WorkItemDb.cs. Add code in Program.cs to handle GET and POST requests for your work items. Run your app and test your endpoints.

You can build your first minimal APIs project very quickly. This easy setup lets you focus on your endpoints and business logic.

Add Endpoints

You can put endpoints right in your Program.cs file. This keeps your code simple and easy to read. To keep things neat, try these tips: Use a base class like RouterBase to handle common CRUD logic. Put route definitions in different classes. This keeps your main file tidy. Make an interface for your route classes. This helps you define endpoints the same way.

Grouping endpoints by feature makes your minimal APIs easier to manage and grow.

Organize Code

Organizing your code helps your project stay clear and easy to change. Try these ideas: Group similar endpoints together. This keeps your code neat. Use handler classes for each feature. This makes testing easier. Cut down on repeated code by using extension methods.

• Grouping endpoints helps you find and fix problems faster. Handler classes make your code easier to test and use again.

Clean code matters. Use good names and keep your formatting the same. This helps everyone on your team understand the project.

Handle Dependencies

You can manage dependencies in minimal APIs with dependency injection. This makes your code easier to test and change. Here are some ways to do it: Register your services with methods like AddTransient, AddScoped, or AddSingleton. Pass dependencies right into your endpoint handlers. This keeps your design simple. Property injection is not used much, but you can use it with some third-party containers.

For example, you can register a service in your Program.cs file:

builder.Services.AddScoped<IWorkItemService, WorkItemService>();

Dependency injection helps you make minimal APIs that are flexible and easy to keep up.

Error Handling

Error handling keeps your minimal APIs working well and easy to use. Here are some ways to handle errors: Add middleware to catch errors everywhere in your app. This puts error responses in one place. Use Problem Details to send clear error messages to users. Check models before you use them. This stops many errors.

You can make a filter to handle exceptions for all endpoints. Use the IEndpointFilter interface and put your logic in a try-catch block.

Exception handling is important. Filters let you use the same error logic for many routes.

Write down your API and error responses. Good documentation helps users and developers do well.

Testing & Docs

Test Endpoints

Testing your minimal API endpoints helps you catch bugs early and keep your code strong. You should separate unit tests from integration tests. This keeps your tests clear and easy to manage. For unit tests, use classes like IResult to check your route handlers. You do not need to set up the whole web server for these tests.

For integration tests, follow the Arrange, Act, Assert pattern. Here is a simple way to do it:

1. Set up your web host for testing.

2. Create a test server client.

3. Arrange your request.

4. Act by sending the request and getting the response.

5. Assert that the response matches what you expect.

Tip: Keep your unit and integration tests in different projects. This makes your codebase easier to maintain.

Add Swagger

Swagger makes your API easy to understand and use. It gives you a clear, language-agnostic way to show what your API can do. You can use Swagger to create a user interface for testing your endpoints. This helps both humans and machines connect to your API quickly.

• Swagger cuts down the time you spend writing documentation.

• It lets you test your API methods right from the browser.

• You can see all your endpoints and their details in one place.

To add Swagger, use the following code in your Program.cs:

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

app.UseSwagger();
app.UseSwaggerUI();

Migration Tips

You can move from traditional APIs to minimal APIs step by step. Start by converting one route or controller at a time. This lets you keep your app running while you update it.

• Use incremental migration for large projects. This follows the Strangler Fig pattern.

• You do not need to change everything at once. Move at your own pace.

• Minimal APIs work well with existing code, so you can mix old and new styles.

Note: Gradual migration helps you avoid big risks and keeps your app stable during changes.

---

Now you know how to make minimal APIs in .NET Core. The setup is simple and the speed is good. Here are some important things to remember:

• Minimal APIs are great for cloud apps, microservices, and quick tests.

• You can add more features with dependency injection, middleware, and OpenAPI.

• Put your code in different files to make it easier to read and use again.

Keep learning new things! Try out advanced features like better API writing and improved form binding.

Here are some next steps to help your project grow:

1. Add error messages so users get clear JSON replies.

2. Change JSON settings to make sure everything works together.

3. Set up CORS rules to keep your app safe.

4. Use output caching to make your app faster.

5. Move your routes into other files to keep things neat.

FAQ

What is the main benefit of using minimal APIs?

You can make web APIs faster with less code. Minimal APIs help you focus on your endpoints and logic. You do not need controllers or extra files. This makes your project simple and easy to handle.

How do you add authentication to a minimal API?

You add authentication by using builder.Services.AddAuthentication() in your Program.cs file. Next, use app.UseAuthentication() before your endpoints. This setup helps you keep your API routes safe.

Can you use dependency injection in minimal APIs?

Yes! You register your services with builder.Services.AddScoped, AddSingleton, or AddTransient. Then, you put them into your endpoint handlers as parameters. This keeps your code neat and easy to test.

How do you organize large minimal API projects?

You split your endpoints into different files or classes. Use extension methods to group similar routes. This keeps your Program.cs file short and your project easy to grow.

Do minimal APIs support OpenAPI/Swagger documentation?

Absolutely! You add Swagger support with:

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

Swagger gives you a user interface to test and explore your API. This helps you and your users learn about your endpoints.