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Chapter 14 · APIs

How Software Talks

API design, development, security, and integration best practices.

Every app you use — weather, payments, maps, login with Google — runs on APIs. Learn how software talks to software: REST, HTTP methods, JSON, status codes, authentication and webhooks, all in plain English.

RESTHTTP MethodsJSONStatus CodesAuthenticationWebhooks
📍 Chapter Overview
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Foundations
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REST & HTTP
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Data Formats
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Authentication
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Integration
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What Is an API
The contract that lets two programs exchange data safely
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REST & HTTP Methods
GET, POST, PUT, DELETE — the verbs of the web
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JSON
The universal data format APIs speak
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Status Codes
200 OK, 404 Not Found, 500 Error — what responses mean
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API Keys & OAuth
How APIs know who's calling and what they're allowed to do
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Webhooks
Reverse APIs — servers that call you when something happens

The API Request/Response Cycle

One API Call, Step by Step GET /weather?city=delhi query Your App Weather app on your phone API Server Checks your key, runs the logic Database Finds today's weather data 200 OK {"city":"Delhi","temp":31,"sky":"clear"} Request goes out, JSON comes back — the whole cycle usually takes under 200 milliseconds

Every tap in a modern app triggers this cycle: your app asks an API, the API asks its data sources, and a structured JSON answer travels back

All guides in this chapter

Beginner
10 min

What is an API? REST, HTTP Methods and JSON Explained for Beginners

The restaurant-menu analogy, a real request walkthrough, HTTP verbs, status codes, and why every modern app depends on APIs.

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Intermediate
10 min

REST vs GraphQL vs gRPC: Choosing the Right API Architecture

Compare REST, GraphQL, and gRPC across performance, caching, and tooling to choose the right architecture for your next service.

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Intermediate
10 min

API Authentication Explained: API Keys, OAuth 2.0, and JWT

How API authentication actually works — API keys, OAuth 2.0, and JWT explained, with what each proves and when to use them.

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Intermediate
10 min

API Versioning Strategies: URI, Header, and Content Negotiation

API versioning strategies explained: compare URI, header, and content negotiation approaches, plus deprecation policy for public APIs.

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Advanced
13 min

API Rate Limiting and Throttling: Algorithms and Implementation

A technical guide to rate limiting algorithms — fixed window, sliding window, token bucket, leaky bucket — and how to implement them correctly.

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Advanced
10 min

API Gateway Patterns: Routing, Aggregation, and Backend for Frontend

API gateway patterns explained for microservices: routing vs aggregation, the BFF pattern, and where the gateway becomes a bottleneck.

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Advanced
10 min

OWASP API Security Top 10 Explained

A practical walkthrough of the OWASP API Security Top 10, with real-world BOLA examples and fixes engineers can apply today.

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Articles in Api