Must-Know API Concepts Every Developer Should Understand

Building an application today almost always involves communicating with a server. Whether you are building a mobile app or a microservice, understanding how APIs function is critical. Let’s dive into the 16 must-know concepts for system design and API development.

1. Architectural Styles: REST, GraphQL, & gRPC

These define how the client and server talk to each other.

• REST: The industry standard. It uses standard HTTP methods (GET, POST, PUT, DELETE) and treats everything as a “resource.”
• GraphQL: Instead of the server defining the response, the client asks for exactly what it needs. This prevents “over-fetching” (getting too much data).
• gRPC: Built by Google, it uses Protocol Buffers (binary data) instead of JSON. It’s incredibly fast and perfect for internal microservices.

Example: A REST GET Request

Kotlin (Using Retrofit):

Kotlin

interface ApiService {
    @GET("users/{id}")
    suspend fun getUser(@Path("id") userId: String): User
}

Dart (Using http):

Dart

Future<User> fetchUser(String userId) async {
  final response = await http.get(Uri.parse('https://api.example.com/users/$userId'));
  return User.fromJson(jsonDecode(response.body));
}

2. Managing Traffic: API Gateway, Rate Limiting, & Throttling

When your app grows, you need to manage the “flood” of traffic.

• API Gateway: A single entry point that sits in front of your services. it handles routing, authentication, and logging.
• Rate Limiting: Restricts how many requests a user can make in a specific timeframe (e.g., 100 requests per minute).
• Throttling: Similar to rate limiting, but usually used to slow down a user who is hogging resources to maintain system stability.

3. Reliability: Timeouts, Retries, & Idempotency

• Timeouts: Prevents a request from hanging forever. If the server doesn’t respond in say, 5 seconds, the client gives up.
• Idempotency: A fancy word for a simple concept: making the same request multiple times should have the same effect as making it once. (Crucial for payments!)

Example: Idempotency in a POST request

In a payment API, you often send a unique Idempotency-Key in the header. If the network drops and you retry, the server sees the key and knows not to charge the user twice.

4. Security: Authentication vs. Authorization

• Authentication: “Who are you?” (e.g., Logging in with a password or JWT).
• Authorization: “What are you allowed to do?” (e.g., An ‘Admin’ can delete users, but a ‘Guest’ cannot).

Dart (Adding a JWT Bearer Token):

Dart

var headers = {
  'Authorization': 'Bearer $your_jwt_token',
  'Content-Type': 'application/json',
};

5. Efficiency: Pagination, Caching, & JSON

• Pagination: Don’t load 10,000 items at once. Load page 1, then page 2.
• Caching Headers: Tells the browser/app: “Don’t ask me for this data again for 10 minutes; use what you already have.”
• JSON: The lightweight, human-readable format used to exchange data.

Kotlin (Pagination Logic):

Kotlin

// Requesting page 2 with 20 items per page
val response = apiService.getProducts(page = 2, size = 20)

6. Real-time & Evolution: Webhooks & Versioning

• Webhooks: Instead of the app asking “Is it done yet?” (Polling), the server “pushes” a notification to the app when something happens.
• Versioning: APIs change. By using /v1/ or /v2/ in your URL, you ensure that old versions of your app don’t break when you update your server code.
• HTTP Status Codes: The “language” of the response.
  • 200 OK: Success.
  • 404 Not Found: The resource doesn’t exist.
  • 500 Internal Server Error: The server crashed.

Summary Table