API fundamentals

What you will be able to do

Skills you add to your Herizon profile when you finish: REST APIs, HTTP.

• What APIs are and why they matter in today's software
• How HTTP methods (GET, POST, PUT, DELETE) work and what status codes mean
• How JSON works and why it's the standard data format for APIs
• How to make API requests with tools like curl and Postman
• How API authentication works, including API keys and OAuth basics
• How to read and find your way around API docs
• How to build a simple API endpoint from scratch
• How to handle errors well in API requests and responses
• How rate limiting (429 and Retry-After) and pagination work and why they exist
• How real APIs like Stripe, GitHub, and weather services are built
• How to put it all together in an API package of your own

Who it is for

Developers, people who want to become developers, or anyone who works with software. It's for you if you want to know how different systems talk to each other. Maybe you're building a frontend that needs data from a backend. Maybe you're connecting a third-party service. Or maybe you're just curious how apps work on the inside. You don't need any API experience. You should know what a web browser does. You should also be at ease with simple coding ideas like variables and functions.

The situation you work through

Elias, a junior developer at Tuulia Apps, a small studio in Helsinki, builds a forecast card that shows 12 degrees from a weather API, reads and creates the user cards 42 and 43, writes a to-do API, then fetches a list of 250 users in pages of 25 without passing a limit of 60 requests a minute.

Your practice task

Build an API package for a free public API you pick. Read its docs and send one request, then run the docs example as it is and change one thing. Build a small API of your own with four endpoints (list, one by id, create, delete) that answers 404 for a missing id and 400 for a missing field, and test it with curl. Write an error plan for the three places a request can fail, and a limits plan with a rule for a 429 and a loop that fetches every page. Submit it as one page without any keys.

What is inside

1. What is an API
2. HTTP methods and status codes
3. JSON and data formats
4. Making API requests
5. Authentication
6. Reading API documentation

and 5 more pages

Finish with a short quiz to earn your certificate.