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Learn REST APIs

Understand how apps talk to servers over HTTP, then build your own.

Free to start. Built from a single prompt. No credit card.

A REST API is a web interface that exposes data as resources at URLs and lets clients act on them with standard HTTP methods like GET, POST, PUT, PATCH and DELETE. The style comes from Roy Fielding's 2000 dissertation, and its key ideas are stateless requests, uniform URLs and meaningful status codes such as 200, 201, 404 and 500. Most REST APIs exchange JSON. Nearly every web and mobile app relies on them, so the skill pays off for front-end, back-end and data work alike. Learnr builds a personalized REST API course and teaches it with short lessons and real requests.

How to learn REST APIs, step by step

Learn how an HTTP request is built. Understand the method, URL, headers, body and the response status line. Open your browser's network tab on any site and inspect real requests until the parts feel familiar.
Call public APIs by hand. Use curl or Postman to fetch weather or a list of countries from a free public API. Send a POST with a JSON body to a test service and read the response headers as well as the data.
Memorize the methods and common status codes. Know that GET reads, POST creates, PUT replaces, PATCH updates part and DELETE removes. Learn which are idempotent, and the difference between 400, 401, 403, 404 and 409.
Design clean resource URLs. Sketch an API for a library, using nouns like /books and /books/42/loans rather than verbs like /getBook. Plan filtering with query strings, pagination with limit and cursor, and a versioning approach.
Build a small CRUD API. Create one with Express in Node.js, FastAPI or Flask in Python, or another framework you know. Return proper status codes, validate input and send consistent error bodies.
Add auth, tests and documentation. Protect routes with an API key or a JWT bearer token, write tests for each endpoint and describe the API in an OpenAPI file. Learnr's daily lessons help status codes and header rules stick.

What you'll learn

Call APIs with curl, Postman or fetch and read the responses
Choose the right HTTP method and status code for each action
Design resource URLs, query parameters and JSON payloads
Secure endpoints with API keys or bearer tokens
Build and document a small CRUD API with OpenAPI

What's inside your REST APIs course

A sample path Learnr builds for REST APIs. Your real course adapts to your goal and level.

1. HTTP basics: requests, responses and headers
2. Methods, status codes and idempotency
3. Calling real APIs and handling JSON
4. Designing resources, filtering and pagination
5. Authentication, rate limits and CORS
6. Building, testing and documenting an API

How long does it take to learn REST APIs?

Calling and understanding REST APIs takes 1 to 2 weeks for someone who can code a little. Designing and building a solid API with auth, validation and docs usually takes 1 to 3 months at 5 hours a week.

What you need before you start

Basic programming in one language, such as JavaScript or Python, and comfort with JSON. Knowing what a URL and a web server are is enough networking background.

Common mistakes to avoid

Returning 200 OK with an error message in the body. Use the status code that matches the outcome so clients can react correctly.
Putting actions in URLs, like /deleteUser?id=5. Use resource paths with the right method, such as DELETE /users/5.
Sending API keys from front-end code where anyone can read them. Keep secrets on a server and call the API from there.

How Learnr builds your course

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REST APIs questions, answered

What is the difference between an API and a REST API?

An API is any defined way for programs to talk to each other. A REST API is a specific style of web API built on HTTP methods, resource URLs and stateless requests.

Should I learn REST or GraphQL first?

Start with REST. It teaches the HTTP fundamentals that GraphQL also runs on, and most public APIs you will meet are REST APIs.