API: What the word actually means

API stands forApplication Programming Interface– an interface that allows one program to communicate with another. Think of it like a waiter in a restaurant:

  • You (the client) are asking for a right

  • The waiter (the API) takes your order to the kitchen

  • The kitchen (system) prepares the food and sends it back

  • The waiter delivers the answer to you

You don't need to know how the kitchen works - just how to order.

REST API: the most common variant

Most web-based APIs today areREST APIs(Representational State Transfer). They communicate via HTTP and use four basic methods:

Method

What it does

GOAT

Retrieving data

MAIL

Creates new data

PUT/PATCH

Updates existing data

DELETE

Deletes data

The response is almost always delivered in JSON format, which looks something like this:

{
  "name": "Zorc",
  "city": "Stockholm",
  "founded": 2022
}

Authentication: How does the API know who you are?

Most APIs require you to identify yourself with oneAPI key– a long, unique string you include in each call. Do not lose it and never put it in public code.

Modern APIs often use OAuth 2.0 for more complex authentication, e.g. 'Sign in with Google'.

Why APIs are so important in 2026

Today, almost no digital service is built completely from scratch. Instead, you put together the best of existing APIs:

  • Stripe– payments

  • Travel / SendGrid– e-mail

  • OpenAI– AI features

  • Google Maps– maps and geolocation

  • Twilio– SMS and telephony

This is sometimes referred to asAPI-firstarchitecture and is the standard for modern web services.

GraphQL and the new landscape

REST is not the only option.GraphQL(developed by Meta) allows the client to specify exactly what data it wants in a single call - reducing over-fetching and under-fetching. It is used by many major platforms such as GitHub and Shopify.

tRPCis a newer option popular in the TypeScript/Next.js ecosystem – it provides full server-to-client type safety without even having to define an API schema.

Good to know before you start

  • Rate limiting: most APIs limit how many calls you can make per minute/hour.

  • Webhooks: instead of you polling an API it canpushdata to you when something happens.

  • API documentation: learn to read it – it's the most important skill in API integration.

Summary

APIs aren't a mysterious concept—they're a well-defined way for programs to talk to each other. REST is the standard, JSON is the language, and authentication via API keys is the rule rather than the exception. The better you understand APIs, the faster you can build high-quality products.