Complete Guide to APIs: Types, Protocols, and Real-World Use Cases

In today’s fast-paced digital world, APIs (Application Programming Interfaces) are the backbone of modern software development. Whether you’re using WhatsApp, checking Google Maps, or making a UPI payment—APIs are working silently in the background.

But here’s the catch—not all APIs are the same.
There are different types of APIs (like Open, Internal, Composite), and different architectures/protocols (like REST, SOAP, GraphQL, WebSocket, gRPC) used to implement them.

This blog will give you a complete understanding of APIs, with examples you can relate to. 🔥

---

What is an API?

An API allows two software systems to communicate with each other by exposing functionality or data.

Imagine an API as a waiter in a restaurant: you (the client) ask for a dish, the waiter takes your order to the kitchen (server), and brings back your food (response).

---

Types of APIs (Based on Access Level)

🔹 1. Open APIs (Public APIs)

• Available to everyone

• No or minimal authentication needed

Example:
Google Maps API – Used in delivery apps like Zomato, Uber to display live locations.

Use Case: Expand app ecosystem, reach third-party developers.

---

🔹 2. Partner APIs

• Shared only with authorized business partners

• Require API keys, contracts, and access approval

Example:
PayPal Payment Gateway API – Only approved platforms like Shopify or Razorpay can use it.

Use Case: B2B integrations with access control.

---

🔹 3. Internal APIs (Private APIs)

• Used within a company

• Not exposed to outside world

Example:
Netflix APIs – Used internally to deliver personalized recommendations and manage user sessions.

Use Case: Microservices communication, internal automation

---

🔹 4. Composite APIs

• Combine multiple APIs into a single call

• Ideal for improving performance

Example:
Travel app making a single call to fetch flight + hotel + taxi info.

Use Case: Microservices, faster client-side performance.

---

API Protocols / Architectural Styles (How APIs Work)

Once you decide who can access your API, the next decision is how it should work. That’s where API protocols come in.

---

🔸 1. REST API (Representational State Transfer)

✅ Most popular style for web and mobile apps

• Works over HTTP

• Uses verbs: GET, POST, PUT, DELETE

• JSON data format

Example:

GET https://api.github.com/users/devdaily

Use Case: Twitter API, GitHub API, e-commerce backend

---

🔸 2. SOAP API (Simple Object Access Protocol)

XML-based, strict and secure

• Heavy structure with envelope, header, and body

• Best for banking, finance, and enterprise apps

Example:
Axis Bank core banking system APIs.

Use Case: Where reliability, transactions, and security matter more than speed.

---

🔸 3. GraphQL API

Ask exactly what you need

• Created by Facebook

• Uses one endpoint

• Returns only requested fields

Example Query:

{
  user(id: "1") {
    name
    email
  }
}

Use Case: Mobile apps with limited bandwidth or dynamic UI.

---

🔸 4. WebSocket API

Real-time 2-way communication

• Keeps an open connection between client & server

• Instant updates without polling

Use Case:
Live chat apps, stock price tickers, gaming platforms

---

🔸 5. gRPC (Google Remote Procedure Call)

⚡ Super-fast, binary communication

• Uses Protocol Buffers (not JSON)

• Designed by Google

• Ideal for microservices and internal APIs

Use Case:
Large-scale backend systems, real-time microservices (used by Netflix, Kubernetes)

---

Summary Table

---

Understanding Types of APIs and how they communicate is essential for every developer, architect, and business strategist today.

• Choose Open APIs to grow your ecosystem.

• Use Internal or Partner APIs to protect your business logic.

• Select REST for simplicity, GraphQL for flexibility, and gRPC for speed.

APIs aren’t just technical tools—they're powerful business enablers. The better you understand them, the more effective and scalable your apps become. 💡

---

Happy coding! ✨

👉 Found this helpful? Follow DevDaily for more developer blogs every week!

✍ Written by Rishabh Mishra