APIs 101#

Software doesn't have to do everything on its own. Instead of reinventing the wheel every time you build an app, you can use the best features from other software inside your new app to do more with less work.

All it takes are APIs.

What is an API?#

API or Application Programming Interface is the tools and functions that let software access functions and features from one application in another. The same way standard plugs and cables let you charge and connect your devices, APIs give you a standardized way to share features and data between software. They're the language software use to talk with each other.

In native Windows or macOS software, for instance, APIs let applications use standard window frames and menus so developers only have to worry about coding the new features they've dreamed up for their app. They're most commonly used to access features built into your device's operating system.

On the web, APIs often take a different role, connecting separate apps to help them work together. Say you want your app to send emails via Gmail. Instead of coding your own email tool and having your users add their Gmail server settings, you could use Gmail's API to access Gmail's messages.send method to send emails with only a few lines of code. Whenever you see an integration that lets you use features from one application in another, those are powered by APIs.

Instead of needing to use an entire app, APIs let you access specific functions when your app needs them. They're the best way to use two apps together.

When a program needs to get data from another piece of software, it will make an API call to the app's API endpoint, letting it know what data it needs along with the API key or OAuth authentication to connect to that app's data. The other app will then send an API response back with the data, where the first app can translate and use that data or function on its own.

APIs define the language, syntax, and functions used to access features in another app. They're each unique—while APIs are often similar to each other, every app's API are often somewhat different with their phrasing and function names. Typically developers need to create a unique integration with each application's API to ensure everything is translated correctly, unless you integrate with an integrations platform like Zapier that handles the translations automatically.

Here are some common terms you'll want to keep in mind while working with APIs:

API Common Terms and Definitions#

  • API: Application Programming Interface, the set of tools, functions, and syntax used to access functionality and data from one application in another.
  • API Authentication: The methods used to verify access to an app's API, especially for accessing user-specific and private data.
  • API Key or API Token: A unique alphanumeric identifier used to access an API, often used to verify an individual user of an API.
  • OAuth: A method to automatically generate API keys or tokens through an app login model, used as a simpler and more secure way to authenticate users on an API.
  • API Endpoint: The unique URL used to access an API or send data back to another application.
  • API Call or API Request: A message from one app to another application's API endpoint, with new data for the app or a query asking for new data from that app.
  • API Response: A reply message from the application that received the API request, including the data requested or a confirmation that new data was received.
  • REST API: An online API that sends and receives data via HTTP requests, including GET, PUSH, and POST calls, and typically serializes data requests and responses in JSON or XML formats.
  • Webhook: A serialized message or notification sent from one application to another's unique URL over the web, often used as a simpler alternative to APIs. Learn more in Zapier's Webhooks Guide.

Learn More about APIs with Zapier's API Book#

Zapier An Introduction to APIs book

Now that you've learned what APIs are, it's time to start using them. Zapier's An Introduction to APIs book is a great place to start. Written by Zapier platform engineering lead Brian Cooksey, it walks you through the basics of APIs, with details on API authentication, design, data formatting, protocols, and implementing them into your application. Each chapter includes an interactive exercise, too, so you can build your skills on a real API right inside the book.

Download a free copy of Zapier's An Introduction to APIs book.

Further Reading#

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