Introduction to APIs: REST vs RPC

💻 Speak the language of software communication

An API (Application Programming Interface) is a set of rules and protocols that allows different software systems to talk to each other. APIs define how requests are made, what data is exchanged, and how responses are structured. Whether you’re building web apps, mobile apps, or backend services, APIs are the bridge that connects everything.

In this guide, you’ll learn what APIs are, the two popular styles — REST and RPC — and how they differ in design and usage.

📁 What is an API Used For?

Connecting frontend applications to backend servers
Accessing data stored remotely
Integrating third-party services (payment gateways, social media, maps)
Enabling modular, reusable software components
Automating workflows between software systems

🧱 API Basics

APIs allow a client (your app) to send requests to a server and receive responses. Requests can ask for data, create new entries, update information, or delete records.

Example: When you order a taxi via an app, the app’s API sends your location and request to the server, which finds a driver and returns confirmation.

🔹 Two Popular API Styles

Style	What it Focuses On	How it Works	Typical Data Format
REST	Resources (data entities)	Uses HTTP methods (GET, POST, PUT, DELETE) on URLs representing resources	JSON, XML
RPC	Actions/Procedures (methods/functions)	Calls methods directly with parameters	JSON-RPC, XML-RPC

REST (Representational State Transfer)

🌐 Resource-oriented, HTTP-based design

REST treats everything as a resource identified by a URL. Clients use standard HTTP verbs to perform actions:

HTTP Verb	Action	Example
GET	Retrieve data	GET /users/123 (get user 123)
POST	Create new resource	POST /users (create new user)
PUT	Update existing resource	PUT /users/123 (update user 123)
DELETE	Remove resource	DELETE /users/123 (delete user 123)

Key Characteristics:

Stateless: Each request contains all necessary info; no session info on server.
Uniform interface: Clear, standardized operations.
Scalable and cacheable.
Ideal for CRUD (Create, Read, Update, Delete) operations.

RPC (Remote Procedure Call)

⚙️ Action-oriented, procedure call style

RPC APIs focus on calling methods or functions on the server, passing parameters and getting results.

Example RPC Call	Meaning
`createUser(name: "Alice", email: "a@example.com")`	Call method to create user
`deleteUser(id: 123)`	Call method to delete user

Key Characteristics:

Emulates local procedure/function calls over network.
May use JSON-RPC, XML-RPC, or custom protocols.
Can be simpler for complex operations.
Not necessarily tied to HTTP methods or resources.

📌 Summary Table

Feature	REST	RPC
Focus	Resources (data)	Methods (actions)
URL	Represents resources (nouns)	Represents method calls (verbs)
HTTP Methods	Uses GET, POST, PUT, DELETE	Typically single POST with method name and params
State	Stateless	Usually stateless
Data Format	JSON, XML (resource representations)	JSON-RPC, XML-RPC, or others
Use Cases	CRUD APIs, web services	Complex workflows, remote commands

🧠 Best Practices

✅ Use REST when your API primarily exposes data entities with standard CRUD operations
✅ Use RPC when your API needs to perform complex operations or commands not fitting the CRUD model
✅ Keep APIs consistent and well-documented
✅ Use meaningful URL/resource names in REST
✅ Clearly define method names and parameters in RPC

📚 Example Requests

REST Example:

GET /books/42 HTTP/1.1
Host: api.example.com
Accept: application/json

Response:

{
  "id": 42,
  "title": "The Hitchhiker's Guide to the Galaxy",
  "author": "Douglas Adams"
}

RPC Example (JSON-RPC):

{
  "jsonrpc": "2.0",
  "method": "getBook",
  "params": { "id": 42 },
  "id": 1
}

Response:

{
  "jsonrpc": "2.0",
  "result": {
    "id": 42,
    "title": "The Hitchhiker's Guide to the Galaxy",
    "author": "Douglas Adams"
  },
  "id": 1
}

🔜 What’s Next?

APIs power modern web and mobile apps. Mastering REST and RPC will help you design efficient, scalable services and integrate third-party systems. Try building simple REST and RPC APIs to solidify your understanding!

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