Types of APIs in C# (.NET)

Below is a complete, clear, and real-time–friendly explanation of all important API types in C#, their definitions, how they work, and how to create each one with real-time examples.

In C#, APIs generally fall into 5 major categories:

1. SOAP API – WCF (Windows Communication Foundation)

2. REST API – ASP.NET Web API / ASP.NET Core API

3. gRPC API – High-performance contract-based API

4. Minimal API – Lightweight API in .NET 6+

5. GraphQL API – Query-based API

Below you will find:
✔ Definition
✔ When to use
✔ Real-time example
✔ How to create (steps + sample code)

1. SOAP API using WCF (Legacy – XML Based)

Definition

SOAP stands for Simple Object Access Protocol.
It uses XML for request and response and follows strict rules.

Use Case

• ✔ Banking systems

• ✔ Insurance

• ✔ Enterprise internal communication

• ✔ When strict contract and security is required (WS-Security)

Real-Time Example

Example: "Loan Status API" exposed by a bank to other systems.

How to Create WCF SOAP API in C#

Step 1: Create WCF Service Application

File → New → Project → WCF Service Application

IService1.cs

[ServiceContract]
public interface IService1
{
    [OperationContract]
    string GetLoanStatus(int loanId);
}

Service1.svc.cs

public class Service1 : IService1
{
    public string GetLoanStatus(int loanId)
    {
        return "Status: Approved";
    }
}

web.config

WCF exposes SOAP endpoints automatically.

2. REST API using ASP.NET Web API / ASP.NET Core API

Definition

REST (Representational State Transfer) uses:

• ✔ JSON (default)

• ✔ HTTP verbs (GET, POST, PUT, DELETE)

It is the most commonly used API today.

Use Case

• ✔ Mobile apps (Android/iOS)

• ✔ Web applications

• ✔ E-commerce

• ✔ Third-party integrations

• ✔ Payment gateways

Real-Time Example

"E-commerce Order API", "Login API", "Product API".

How to Create REST API in ASP.NET Core

Step 1: Create Project

File → New → Project → ASP.NET Core Web API

Model

public class Product
{
    public int Id { get; set; }
    public string Name { get; set; }
    public decimal Price { get; set; }
}

Controller

[ApiController]
[Route("api/[controller]")]
public class ProductController : ControllerBase
{
    [HttpGet]
    public IActionResult GetProducts()
    {
        return Ok(new List<string> { "Laptop", "Mobile" });
    }

    [HttpPost]
    public IActionResult AddProduct(Product p)
    {
        return Ok("Product Inserted");
    }
}

3. Minimal API (Introduced in .NET 6)

Definition

Minimal API is a super lightweight REST API created without controllers.

Use Case

• ✔ Microservices

• ✔ Small modules

• ✔ IoT devices

• ✔ Internal APIs

Real-Time Example

“Health Check API”
“Insert Logs API”

How to Create Minimal API

Program.cs

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

app.MapGet("/hello", () => "Hello World");
app.MapPost("/save", (Product p) => $"Saved {p.Name}");

app.Run();

Fastest way to expose endpoints.

4. gRPC API

Definition

gRPC is a high-performance, contract-first, binary communication protocol.
Uses Protocol Buffers (.proto) instead of JSON/XML.

Use Case