Everything about Web API

What is a Web API?

A Web API (Application Programming Interface) is a set of HTTP-based endpoints that allow systems, applications, or devices to communicate over the web.

Examples

• Retrieving weather data from a weather API.

• Sending payments using the Stripe API.

• Fetching user data from your own backend for a mobile app.

Key features

• Communicates using HTTP(S)

• Returns structured data (JSON, XML, etc.)

• Follows REST, GraphQL, or gRPC conventions

• Enables machine-to-machine communication

Types of Web APIs

Type	Description	Example
REST API	Resource-based, uses HTTP verbs (GET, POST, PUT, DELETE)	Twitter API, Shopify API
SOAP API	XML-based, strict contract using WSDL	Legacy banking systems
GraphQL API	Flexible querying, client decides what data to fetch	GitHub GraphQL API
gRPC API	High-performance, uses Protocol Buffers, ideal for microservices	Kubernetes API server
Webhooks	Event-driven callbacks sent to a URL	Stripe sends payment success event

Core Concepts of RESTful Web API

• Resources → Represented by URLs (e.g., /products/123)

• HTTP Verbs →

  • GET = Read

  • POST = Create

  • PUT/PATCH = Update

  • DELETE = Remove

• HTTP Status Codes

  • 200 OK, 201 Created, 400 Bad Request, 401 Unauthorized, 404 Not Found

• Statelessness → Each request is independent, no server-side session

• JSON Format → Most common response payload

Web API Architecture

A typical Web API architecture includes:

1. Client (browser, mobile app, other service)

2. API Gateway / Reverse Proxy (optional, for routing & security)

3. Web API Layer (controllers, endpoints)

4. Business Logic Layer (services)

5. Data Access Layer (database / external APIs)

6. Persistence (SQL, NoSQL)

7. Authentication & Authorization (JWT, OAuth2)

Building a Web API (Step-by-Step)

Example: .NET Web API

1. Create a Project

   dotnet new webapi -n ProductApi
   

2. Define Model

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

3. Create Controller

   [ApiController]
   [Route("api/[controller]")]
   public class ProductsController : ControllerBase {
       private static List<Product> _products = new();
       
       [HttpGet]
       public IActionResult GetAll() => Ok(_products);
   
       [HttpPost]
       public IActionResult Create(Product product) {
           product.Id = _products.Count + 1;
           _products.Add(product);
           return CreatedAtAction(nameof(GetAll), product);
       }
   }
   

4. Run & Test

   • Use Swagger (built into .NET Web API template)

   • Test with Postman or curl

Best Practices for Web APIs

✅ Use Versioning – api/v1/products
✅ Return Proper HTTP Codes – 404 for not found, 400 for bad input
✅ Validation & Error Handling – Always return meaningful errors
✅ Pagination, Filtering, Sorting – For large datasets
✅ Rate Limiting & Throttling – Prevent abuse
✅ Caching – ETag, HTTP cache headers for performance
✅ OpenAPI/Swagger Docs – Self-documenting APIs

Security Considerations

• HTTPS Only – Encrypt all traffic

• Authentication

  • JWT (JSON Web Token)

  • OAuth2 (for third-party integrations)

  • API Keys (for internal systems)

• Authorization – Role-based access (RBAC)

• Input Sanitization – Prevent injection attacks

• CORS Policy – Restrict allowed origins

• Rate Limiting – Protect against DDoS

Testing & Monitoring

• Unit Tests – Test services and controllers

• Integration Tests – Test API endpoints with mock database

• Postman/Newman – Manual and automated testing

• Load Testing – JMeter, k6 for performance testing

• Logging & Tracing – Serilog, OpenTelemetry

• API Monitoring – New Relic, Datadog, Prometheus + Grafana

API Analytics

Track key metrics:

• Request Volume (per endpoint)

• Latency & Response Time

• Error Rate

• Top Consumers (API keys, users)

• Revenue (if monetized)

Real-World Use Cases

• E-commerce → Product catalog APIs, order APIs

• Banking → Payment APIs, transaction APIs

• Social Media → Post, comment, like APIs

• IoT → Device telemetry APIs

• SaaS → Integrations with external CRMs, ERPs