Internet & Tools - APIs & REST Explained

Create a free account to save your progress

Earn XP, track streaks, and sync your dashboard across devices.

Lesson

An APIWhat is api?A set of rules that lets one program talk to another, usually over the internet, by sending requests and getting responses. is a way for one program to use another program's features. Think of it like a menu at a restaurant, you don't need to know how to cook, you just order from the menu and the kitchen does the work. APIs power everything from weather apps to payment processing to social media logins.

What is an APIWhat is api?A set of rules that lets one program talk to another, usually over the internet, by sending requests and getting responses.?

API = Application Programming Interface

It's a contract that defines:

What operations are available
What data format to use (usually JSONWhat is json?A text format for exchanging data between systems. It uses key-value pairs and arrays, and every programming language can read and write it.)
How to authenticate (prove who you are)
What errors mean

When you use an API, you're saying: "I want to use your functionality, but I don't need to see your code. Just tell me what requests to make and I'll handle the restWhat is rest?An architectural style for web APIs where URLs represent resources (nouns) and HTTP methods (GET, POST, PUT, DELETE) represent actions on those resources.."

Real-world API examples

Service	What your app sends	What you get back
Weather API	City name or coordinates	Current temperature, forecast
Google Auth	OAuth token request	User's email and profile
Stripe	Payment card details	Success/failure confirmation
Google Maps	Address or coordinates	Map tiles, directions

Without APIs, every developer would need to build everything from scratch. Want weather data? Build your own weather stations. Want maps? Survey the world yourself. APIs let you stand on the shoulders of giants.

What is RESTWhat is rest?An architectural style for web APIs where URLs represent resources (nouns) and HTTP methods (GET, POST, PUT, DELETE) represent actions on those resources.?

REST = Representational State Transfer

REST isn't a technology or a standard, it's an architectural style. It's a set of conventions for building APIs using HTTPWhat is http?The protocol browsers and servers use to exchange web pages, API data, and other resources, defining how requests and responses are formatted. in a predictable way. RESTful APIs are intuitive because they follow patterns you already understand.

The six REST principles

Client-server architecture: The client and server are separate. They can evolve independently as long as they keep the same interface.

StatelessWhat is stateless?A design where each request contains all the information the server needs, so any server can handle any request without remembering previous ones.: Each request contains all the information needed to process it. The server doesn't remember previous requests. This makes APIs scalable, any server can handle any request.

Cacheable: Responses can be cached. If you request /users/123 twice, the second response might come from a cache, not the server.

Uniform interface: Resources are identified by URLs. You use HTTP methods (GET, POST, PUT, DELETE) to act on them. Responses are self-descriptive.

Layered system: The client doesn't know (or care) if it's talking directly to the server or through intermediaries like load balancers or CDNs.

Code on demand (optional): Servers can send executable code to clients (rarely used in practice).

RESTful URL structure

REST organizes resources hierarchically using URLs:

/users                    → All users (collection)
/users/123                → Specific user (resource)
/users/123/posts          → Posts by user 123
/users/123/posts/456      → Specific post by user 123

Nesting shows relationships. It's intuitive, if you understand /users/123, you can guess what /users/123/posts means.

HTTP methods in REST

REST uses HTTP methods to define actions on resources:

Method	URL	Action	Description
GET	/users	Read all	List all users (possibly paginated)
GET	/users/123	Read one	Get user 123's details
POST	/users	Create	Create a new user
PUT	/users/123	Update all	Replace user 123 completely
PATCH	/users/123	Update some	Change specific fields of user 123
DELETE	/users/123	Delete	Remove user 123

See how predictable this is? Once you learn the pattern, you can interact with any REST APIWhat is api?A set of rules that lets one program talk to another, usually over the internet, by sending requests and getting responses..

A complete RESTWhat is rest?An architectural style for web APIs where URLs represent resources (nouns) and HTTP methods (GET, POST, PUT, DELETE) represent actions on those resources. APIWhat is api?A set of rules that lets one program talk to another, usually over the internet, by sending requests and getting responses. example

Blog API endpoints:

Method	Endpoint	What it does
GET	/posts	List all posts (paginated)
GET	/posts/5	Get post #5
POST	/posts	Create new post
PUT	/posts/5	Update post #5 completely
PATCH	/posts/5	Update part of post #5
DELETE	/posts/5	Delete post #5
GET	/posts/5/comments	Get comments on post #5
POST	/posts/5/comments	Add comment to post #5

Request and response format

Request:

GET /api/users/123 HTTP/1.1
Host: api.example.com
Authorization: Bearer token123
Accept: application/json

Response:

HTTP/1.1 200 OK
Content-Type: application/json

{
  "id": 123,
  "name": "Alice",
  "email": "alice@example.com",
  "posts": 42,
  "createdAt": "2023-01-15T10:30:00Z"
}

Notice the Accept: application/json header, the client is saying "I want JSONWhat is json?A text format for exchanging data between systems. It uses key-value pairs and arrays, and every programming language can read and write it. back." And the server responds with Content-Type: application/json confirming that's what it's sending.

Why JSONWhat is json?A text format for exchanging data between systems. It uses key-value pairs and arrays, and every programming language can read and write it.?

JSON (JavaScript Object Notation) is the standard format for APIs because it:

Is easy to read and write
Is lightweight compared to XML
Works with all programming languages
Is native to JavaScript (most popular web language)
Maps cleanly to objects in most languages

json

{
  "user": {
    "name": "Alice",
    "age": 25,
    "active": true,
    "hobbies": ["coding", "gaming"],
    "address": {
      "city": "Paris",
      "country": "France"
    }
  }
}

APIWhat is api?A set of rules that lets one program talk to another, usually over the internet, by sending requests and getting responses. authenticationWhat is authentication?Verifying who a user is, typically through credentials like a password or token.

Most APIs require authentication to identify who's making the request and control access.

Method	Header example	Best for
API Key	`X-API-Key: abc123xyz`	Server-to-server calls
Bearer Token (JWT)	`Authorization: Bearer eyJhb...`	User-facing apps
OAuth 2.0	Redirect-based flow	"Login with Google" buttons

AI pitfall

AI tools frequently build non-RESTful endpoints like POST /getUsers or GET /deleteUser/123. They also tend to ignore pagination (returning all 10,000 records at once), skip error response bodies (returning just a status code with no message), and forget to version the API. If Copilot generates an endpoint, check: does it use the right HTTP method? Does it return proper error messages? Does the list endpoint support ?page= and ?limit=? A well-designed API should handle the unhappy path, not just the happy one.

RESTWhat is rest?An architectural style for web APIs where URLs represent resources (nouns) and HTTP methods (GET, POST, PUT, DELETE) represent actions on those resources. vs other APIWhat is api?A set of rules that lets one program talk to another, usually over the internet, by sending requests and getting responses. styles

Style	Best for	Pros	Cons
REST	Standard CRUD operations	Simple, standard, easy to cache	Can require multiple requests
GraphQL	Complex data needs	Get exactly what you need	Steeper learning curve
gRPC	Microservices	Fast, type-safe, efficient	Requires HTTP/2, less browser support
WebSocket	Real-time updates	Bidirectional, persistent	More complex, harder to scale

RESTWhat is rest?An architectural style for web APIs where URLs represent resources (nouns) and HTTP methods (GET, POST, PUT, DELETE) represent actions on those resources. best practices

Design:

Use plural nouns: /users not /user
Use nesting for relationships: /users/123/posts
Keep URLs lowercase with hyphens: /user-profiles not /userProfiles
Version your APIWhat is api?A set of rules that lets one program talk to another, usually over the internet, by sending requests and getting responses.: /v1/users, /v2/users

Responses:

Return helpful error messages with details
Use appropriate status codes
Include paginationWhat is pagination?Splitting a large set of results into smaller pages so the server and client only handle a manageable chunk at a time. for lists: /users?page=2&limit=20

Security:

Use HTTPSWhat is https?HTTP with encryption added, so data traveling between your browser and a server can't be read or tampered with by anyone in between. always
Validate all input
Rate limit to prevent abuse
Document your API (OpenAPIWhat is openapi?A standard format for describing REST APIs - their endpoints, parameters, and response shapes. Tools can generate documentation and client libraries from it automatically./Swagger is standard)

Quick reference

Concept	Convention	Example
Resource naming	Plural nouns	`/users`, `/posts`
Get one	GET + ID	`GET /users/123`
Create	POST to collection	`POST /users`
Update	PUT/PATCH + ID	`PUT /users/123`
Delete	DELETE + ID	`DELETE /users/123`
Nested resources	Parent/child	`/users/123/posts`
Filtering	Query params	`?status=active`
Pagination	Query params	`?page=2&limit=20`

Done

Complete & Next

Create a free account to save your progress

Essential to know

What is an APIWhat is api?A set of rules that lets one program talk to another, usually over the internet, by sending requests and getting responses. Ask AI for more?