Minimal Apis
Evaluation Report: Carter for ASP.NET Minimal APIs
Introduction
This report documents findings from working with Carter as a framework for structuring ASP.NET Core Minimal API applications. The purpose is to evaluate how Carter improves development experience when building APIs and how it compares conceptually with other approaches that organize Minimal API endpoints.
Minimal APIs provide a lightweight way to create HTTP APIs without the ceremony traditionally associated with controllers. However, as an application grows, managing endpoints directly inside Program.cs can quickly become difficult. Carter attempts to address this by introducing a modular approach that keeps Minimal APIs clean while maintaining their simplicity.
This report focuses on developer experience, maintainability, structure, and extensibility.
Background: Minimal APIs
Minimal APIs in ASP.NET Core allow developers to define routes directly using methods such as:
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app.MapGet("/users", () => { ... });
This approach reduces boilerplate and is well suited for microservices and small APIs. However, in larger projects several challenges appear:
- Endpoint definitions accumulate inside
Program.cs - Routing logic becomes scattered
- Code organization becomes harder to maintain
- Reuse of validation or middleware patterns becomes inconsistent
Frameworks such as Carter aim to solve these issues while keeping the benefits of Minimal APIs.
Overview of Carter
Carter is a lightweight library that introduces modular routing to ASP.NET Minimal APIs.
The main concept in Carter is the module. Instead of defining endpoints directly in Program.cs, routes are grouped into modules that implement ICarterModule.
Example:
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public class UserModule : ICarterModule
{
public void AddRoutes(IEndpointRouteBuilder app)
{
app.MapGet("/users", GetUsers);
app.MapPost("/users", CreateUser);
}
}
During application startup Carter scans and registers these modules automatically.
This approach creates a structure similar to controllers but keeps the flexibility and minimal overhead of Minimal APIs.
Setup and Integration
Adding Carter to an existing Minimal API project is straightforward.
First install the package:
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dotnet add package Carter
Register Carter services:
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builder.Services.AddCarter();
Map Carter modules:
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app.MapCarter();
Once configured, the framework discovers modules and registers routes automatically.
The setup process is simple and introduces very little additional complexity compared with raw Minimal APIs.
Key Features
Modular Endpoint Organization
The primary benefit of Carter is modularization.
Endpoints are grouped logically based on domain or feature. For example:
- UserModule
- ProductModule
- OrderModule
This makes it easier to navigate large projects and reduces clutter in the main application entry point.
Separation of Concerns
By moving endpoint definitions into modules, the main application configuration becomes cleaner.
Program.cs focuses only on:
- application startup
- dependency registration
- middleware configuration
Business logic and route definitions live elsewhere.
Integration with ASP.NET Core Features
Carter works naturally with existing ASP.NET Core functionality including:
- dependency injection
- middleware
- authentication and authorization
- request binding
- response handling
Developers do not need to learn a completely new abstraction layer.
Request Validation
Carter supports validation through integration with libraries such as FluentValidation.
This allows validation logic to be applied cleanly to incoming requests without cluttering endpoint handlers.
Example concept:
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public class CreateUserValidator : AbstractValidator<CreateUserRequest>
{
public CreateUserValidator()
{
RuleFor(x => x.Name).NotEmpty();
}
}
This approach keeps validation logic separate from route logic.
Automatic Discovery
Carter automatically scans the application for modules that implement ICarterModule.
This removes the need to manually register each route group and helps keep configuration simple.
Developer Experience
From a developer perspective Carter improves the experience of working with Minimal APIs in several ways.
Improved Code Structure
Large Minimal API projects often become difficult to manage when routes accumulate in a single file. Carter solves this by distributing endpoints across modules.
Developers can quickly locate routes associated with a particular feature.
Reduced Startup File Complexity
In standard Minimal API projects the Program.cs file can become very long.
Carter keeps this file minimal and focused on configuration rather than endpoint logic.
Familiar but Lightweight Pattern
Developers coming from MVC controllers often find Carter easier to understand because it introduces logical grouping without requiring the full controller framework.
At the same time it avoids the heavier structure associated with controllers.
Performance Considerations
Carter is essentially a thin organizational layer over ASP.NET Minimal APIs. It does not introduce a heavy runtime abstraction.
The routing and execution model still relies on the underlying ASP.NET Core infrastructure. As a result performance differences compared with raw Minimal APIs are generally minimal.
Startup time may include module scanning, but the overhead is typically negligible in most applications.
Limitations
While Carter improves organization, it also introduces a few considerations.
Additional Dependency
Projects must include an additional package, which adds a small layer of abstraction.
For teams that prefer pure framework solutions this may be undesirable.
Convention Based Structure
Carter encourages a modular convention. While this improves consistency, it may limit flexibility if a project requires very custom routing structures.
Learning Curve
Developers unfamiliar with Carter must learn its module based approach, though the learning curve is relatively small.
Use Cases Where Carter Works Well
Carter is particularly useful in the following scenarios:
- medium sized Minimal API projects
- microservices with multiple route groups
- teams that want better structure without moving to full MVC controllers
- projects that need clean separation of endpoint logic
It may be less necessary in very small APIs where only a few endpoints exist.
General Comparison Direction with FastEndpoints
Although a detailed comparison will be handled separately, some conceptual differences can be observed.
FastEndpoints focuses on defining endpoints as strongly structured classes with built in validation and request handling patterns.
Carter instead focuses mainly on organization and modular routing, while still relying on native ASP.NET Minimal API patterns.
In simple terms:
- Carter organizes Minimal APIs
- FastEndpoints introduces a more opinionated endpoint architecture
This difference affects how much structure the framework enforces.
Conclusion
Carter provides a simple and effective way to organize **ASP.NET Core Minimal APIs. Its modular design helps maintain clean project structure while preserving the lightweight nature that makes Minimal APIs attractive.
The framework integrates naturally with existing ASP.NET Core features and introduces minimal overhead. For teams building APIs that are larger than simple prototypes but do not require full MVC controllers, Carter offers a balanced solution.
Its main value lies in improving code organization, maintainability, and developer experience without significantly altering the core Minimal API development model.
Happy Coding!