The API Handbook: Every Type You Must Know

Source: Dev.to

If you’ve ever wondered how your favorite apps seem to magically talk to each other—like how Google Maps appears inside a ride‑sharing app—you’ve seen an API at work. At its core, an API (Application Programming Interface) is simply a set of rules that allows different software applications to communicate and exchange data with one another.

Think of it like a translator who helps two people speaking different languages have a conversation. In the digital world, an API is that translator for software. This guide walks you through the seven most common types of APIs, using simple analogies to help you understand what makes each one unique and when you might use it.

1. REST API – The Universal Waiter

A REST API is the most common and flexible type of API you’ll find on the web today.

Analogy: Think of a REST API like a waiter at a restaurant. You (your app) tell the waiter what you want from the menu, the waiter goes to the kitchen (the server), gets it, and brings it back to you.

What “REST” means: Representational State Transfer – a formal way of describing a simple and standard approach for applications to talk over the internet.

Key Characteristics

• Uses Standard HTTP Methods – the same simple, familiar actions that web browsers use, making it intuitive for developers.

  Method	Purpose	Example
  GET	Retrieve data	“Show me this user’s profile.”
  POST	Create something new	“Add this new user.”
  PUT	Update existing data	“Update this user’s email.”
  DELETE	Remove data	“Delete this user.”

• Stateless – each request is completely independent. The server doesn’t remember anything about previous requests, which simplifies the system and lets it handle millions of users simultaneously without getting confused.

• Platform‑Independent (JSON) – REST commonly uses JSON (JavaScript Object Notation), a clean, text‑based data format. This makes it easy for any type of application—whether it’s on iPhone, Android, or a website—to use the same API.

When to use: Perfect for building general‑purpose applications, like a social‑media app where you need to fetch user profiles and post updates.

Note: REST is incredibly flexible and popular, but for situations demanding high security and formal rules (e.g., a bank transfer), a more structured approach may be needed.

2. SOAP API – The Formal Business Contract

Before REST became the standard, SOAP was the dominant choice for enterprise‑level communication.

Analogy: If REST is a casual phone call, SOAP is a formal business contract. Every message must follow strict rules and comes wrapped in a very specific structure.

What “SOAP” means: Simple Object Access Protocol – an older, more formal communication method that requires all messages to be formatted in a strict, XML‑based structure containing an envelope, a header, and a body.

Key Strengths

• Protocol Independent – While SOAP often uses HTTP (like REST), it isn’t limited to it. It can also run over other protocols such as SMTP (email), providing flexibility in certain enterprise environments.

• Built‑in Standards – SOAP includes industry‑standard rules for security, error handling, and transactions. This makes it highly trusted for systems where precision and reliability are non‑negotiable.

Typical Use Cases: Banks, healthcare providers, and government systems still rely heavily on SOAP. For example, when you transfer money between banks, a SOAP API is likely working behind the scenes to ensure the transaction is secure and processed correctly.

Caveat: While SOAP provides enterprise‑grade reliability, modern applications often require raw speed and performance, leading to the creation of high‑performance alternatives.

3. gRPC API – The Formula 1 Race Car

Developed by Google, gRPC is an API built from the ground up for maximum speed and efficiency.

Analogy: Think of gRPC as the Formula 1 race car of APIs—built for speed, performance, and precision.

What “gRPC” means: A modern, high‑performance version of RPC (Remote Procedure Call). RPC lets an application call a function on another machine across a network as if it were a local function. gRPC perfects this concept for today’s massive, real‑time apps.

Why It’s So Fast

• Protocol Buffers (Protobuf) – Instead of sending text‑based JSON like REST, gRPC uses Protocol Buffers, a compact binary format that compresses data, making it much faster to process and transmit.

• HTTP/2 – gRPC runs on HTTP/2, which allows multiple requests to share a single connection simultaneously, dramatically improving efficiency.

• Advanced Communication Patterns – Beyond simple request‑response, gRPC supports:

  • Server streaming – live updates from server to client.
  • Client streaming – continuous data sent from client to server.
  • Bidirectional streaming – both sides “chat” in real time.

Performance gains are massive; gRPC is often 7–10× faster than a comparable REST API. This is why it powers performance‑critical systems at companies like Netflix and Uber.

Best For: Server‑to‑server communication where speed is paramount.

4. GraphQL API – The Precision Shopper

Created by Facebook, GraphQL is a revolutionary way to fetch data that solves common frustrations developers have with REST APIs. Its main goal is to prevent over‑fetching (getting too much data) and under‑fetching (not getting enough data and needing multiple requests).

Analogy: With GraphQL, you’re a shopper who tells the clerk exactly what items you want, and the clerk brings back precisely those items—no more, no less.

How It Works

You write one query asking for exactly what you need; a single endpoint processes the request and returns perfect data every time.

Killer Features

• Precise Data Fetching – Ask for just a user’s username and email without receiving their entire profile, saving bandwidth and making mobile apps faster.
• Self‑Documenting – GraphQL APIs come with a built‑in “playground” that lets developers explore the available data and test queries instantly, making them incredibly easy to work with.
• Real‑Time Subscriptions – Allows an application to listen for live data updates automatically, letting the server push changes to the client as they happen.

Major tech companies like GitHub and Shopify have built their entire APIs on GraphQL because it gives front‑end developers the flexibility and efficiency they need.

5. WebHook API – The Doorbell Notification

WebHooks completely flip the traditional API communication model on its head.

• Traditional APIs – Your app constantly checks its “mailbox”: you walk outside, open it, see nothing, and walk back.
• WebHooks – Like the mailman ringing your doorbell the moment a letter arrives—instant, direct, and efficient.

WebHooks are often called “reverse APIs” because, instead of your application polling the server for new information, the server pushes information to your application the moment a specific event happens.

How It Works

1. You provide a callback URL from your app to another service.
2. When an event you care about occurs on that service, it automatically sends a POST request with the event details straight to your URL.
3. No polling, no wasted requests—just real‑time updates.

Common Use Cases

• GitHub fires a WebHook when new code is pushed.
• Shopify triggers a WebHook when a new order is placed.
• Slack and Discord bots rely on WebHooks to react to commands.

WebHooks excel at event‑based notifications, but for continuous, two‑way conversations you need a connection that stays permanently open.

6. WebSocket API – The Open Phone Line

WebSockets are designed for persistent, real‑time, two‑way communication.

• Think of a WebSocket as opening a permanent phone line between your app and the server.
• Once the connection is established, both sides can talk to each other anytime, instantly.

The Handshake

1. The client sends a special HTTP request called a handshake asking the server to upgrade the connection.
2. The server agrees, and from that moment on a persistent, bi‑directional channel is open.

Unlike traditional HTTP where the client must always initiate a request, a WebSocket allows the server to push data to the client at any time. The protocol is flexible—you can send plain text, JSON, or even binary files (images, videos).

Ideal Use Cases

• Live chat messages
• Real‑time stock price updates
• Live game events and scoreboards

WebSockets power many of the instant, interactive experiences you enjoy on the web. They create a powerful client‑server connection, but what if you want to bypass the server entirely and connect two users directly for even faster communication?

7. WebRTC API – The Direct Peer‑to‑Peer Call

WebRTC (Web Real‑Time Communication) enables direct browser‑to‑browser communication. While a server may help the browsers discover each other initially, the actual data—video, audio, and files—flows directly between users in a peer‑to‑peer connection.

• When you’re on a video call, your video and audio are sent straight from your device to the other person’s device—no server in the middle storing or processing your private conversation.
• WebRTC handles all the messy networking details automatically, allowing browsers to find and connect to each other directly, resulting in faster communication with no server bottlenecks.

What It Powers

• Video and audio calls (e.g., Google Meet)
• Screen sharing
• Online gaming
• Instant peer‑to‑peer file transfers

Behind the scenes, WebRTC uses features like adaptive bitrate streaming, which constantly adjusts video quality based on your internet speed to ensure a smooth experience. It provides the backbone for real‑time communication directly in the browser with no extra software required.

At a Glance – Quick Comparison of the Seven API Types

Conclusion

There is no single “best” API. Each type was designed to solve a specific kind of problem. A REST API is a versatile workhorse for general‑purpose use, but it can’t provide the real‑time push notifications of a WebHook or the peer‑to‑peer speed of WebRTC. Understanding the strengths and weaknesses of each allows you to choose the right tool for any job.

By learning these core concepts, you’ve taken a crucial step toward understanding how the modern digital world is built. As you continue your journey as a developer or tech enthusiast, you’ll be well‑equipped to select the appropriate API type for any challenge.