As software architects, our job is rarely about choosing the “coolest” tool. It is about choosing the tool that minimizes technical debt, maximizes developer velocity, and aligns with the system’s long-term goals.

When evaluating the .NET ecosystem for API development, the choice usually falls between MVC Controllers (structured but heavy) and Minimal APIs (fast but potentially messy).

FastEndpoints is often the missing link in this decision matrix. It is not just a library; it is an enforcement mechanism for the REPR (Request-Endpoint-Response) pattern. Below is an analysis of the specific requirements and architectural scenarios where FastEndpoints is the superior choice.

1. When Adopting Vertical Slice Architecture 

If your architectural strategy is moving away from Layered Architecture (Onion/Clean) toward Vertical Slice Architecture, FastEndpoints is the natural implementation tool.

  • The Problem: In traditional controllers, a single file (UserController) often couples unrelated business capabilities (Registration, Profile Updates, Password Reset). Changing one risks breaking the other due to shared private methods or constructor injections.
  • The FastEndpoints Advantage: It enforces physical separation. Each feature is a distinct file. This means high cohesion (code that changes together stays together) and low coupling (unrelated features do not share a class).

2. When Scaling Development Teams 

As teams grow, merge conflicts in “God Classes” (monolithic Controllers or Service classes) become a daily bottleneck.

  • The Requirement: You have multiple developers working on different features within the same domain boundary.
  • The FastEndpoints Advantage: Because every endpoint is a separate class file, Developer A working on GetOrderEndpoint.cs will never have a merge conflict with Developer B working on CreateOrderEndpoint.cs. It aligns perfectly with Conway’s Law, allowing teams to work in parallel with minimal friction.

3. When Performance is a Non-Negotiable 

If you are building high-throughput microservices where every millisecond of latency and every megabyte of memory counts.

  • The Requirement: You need the raw performance of Minimal APIs but cannot afford the spaghetti code that often results from putting all logic in Program.cs.
  • The FastEndpoints Advantage: FastEndpoints sits directly on top of ASP.NET Core’s Minimal APIs. It avoids the MVC pipeline overhead (filters, binders, legacy routing). It builds expression trees at startup for model binding and validation, offering execution speeds nearly identical to raw Minimal APIs but with the structure of a mature framework.

4. When Enforcing Standardization (Governance) 

Architects often struggle to enforce coding standards across large codebases.

  • The Requirement: You need to ensure every API endpoint has consistent validation, logging, and response structures without relying on developers to “remember” to add attributes.
  • The FastEndpoints Advantage: It makes validation a first-class citizen. You cannot easily bypass the pipeline. By connecting FluentValidation automatically, it enforces a standard approach to input sanitization. Unlike Controllers, where validation can be scattered across attributes and service layers, FastEndpoints centralizes it within the slice.

5. When Functional Testing is a Priority 

Unit testing logic inside Controllers is easy, but full Integration/Functional testing of the HTTP pipeline can be verbose in standard ASP.NET Core.

  • The Requirement: You want a “Testing Pyramid” that relies heavily on fast integration tests to ensure the HTTP contract (Route, Request, Response) works as expected.
  • The FastEndpoints Advantage: FastEndpoints ships with a dedicated testing library (FastEndpoints.Testing) designed for Integration Testing. It allows you to invoke endpoints directly in memory with strict typing, making your test suite robust and refactor-safe.
Feature MVC Controllers Raw Minimal APIs FastEndpoints
Architectural Style Layered (Horizontal) Scripting / Micro-service Vertical Slices
Performance Good Excellent Excellent
Cognitive Load High (Bloated classes) Low (initially) -> High (as it grows) Low (One file = One feature)
Testability High (Unit), Med (Integration) Medium High (First-class Integration support)
Team Scalability Low (Merge conflicts) Medium High (File separation)
Enforced SRP No (Easy to violate) No Yes (By design)

The Verdict 

Choose FastEndpoints if:

  1. You are building Microservices or complex Monoliths using Vertical Slice Architecture.
  2. You expect the application to grow significantly in feature count.
  3. You want to enforce the Single Responsibility Principle at the architectural level, preventing “Controller Bloat” before it starts.

Stick to Controllers if:

  1. You are maintaining a legacy ASP.NET Core application and cannot afford a rewrite.
  2. Your team is deeply resistant to new patterns and strictly prefers the “Bucket by Resource” organization.

 

Happy Coding !!!