Understanding API Fundamentals

What is an API?

API stands for application programming interface. APIs are the little pieces of code that make it possible for digital devices, software applications, and data servers to talk with each other, and they’re the essential backbone of so many services we now rely on.

API is an application that we use every day. In an internet-connected world, web and mobile applications are designed for humans to use, while APIs are designed for other digital systems and applications to use. Websites and APIs both do the same things, like return data, content, images, video, and other information. But APIs don’t return all the details that are needed to make things look pretty for the human eye—you only get the raw data and other machine-readable information needed behind the scenes to put the resources being delivered to work, with very little assistance from a human.


What are APIs used for?

· APIs power desktop applications.

· APIs are behind most web applications.

  • APIs make mobile applications possible.

  • APIs are the integrations for no code solutions.

  • APIs connect devices to the internet.

  • APIs define the networks—or the information passed between applications, systems, and devices.

  • APIs even connect everyday things like automobiles, doorbells, dishwashers, and wearable devices.

About APIs?

  • APIs help you access the data you need to get your work done and do daily tasks—whether you’re a business user, a student, or using an application just for fun.

  • APIs make it possible to integrate different systems together, like Customer Relationship Management systems, databases, or even school learning management systems.

  • APIs help different departments, teams, and groups become more agile.

  • APIs help organizations, schools, government agencies, and non-profits strengthen relationships with other organizations, research institutes, and agencies.

The different kinds of APIs


There are many different types of APIs, and many different ways to categorize them. Here are some of most common.

Internal vs. External vs. Partner APIs

One way to categorize APIs is by who has access to them:

  • Internal APIs are APIs that are private and only used by your team, department, company, or organization.

  • External APIs, also known as public APIs or open APIs (which is not to be confused with OpenAPI), are publicly available APIs that are available for anyone to use.

  • Partner APIs are private and shared only with specific, integration partners outside of your organization.

API architectural styles

When it comes to API architecture, there are a number of styles—some newer, some older—and all have a place in the API ecosystem. Defining “architectural styles” broadly, here is a list of the most popular styles listed in order of how frequently they’re used:

  • REST API: REST is an acronym for Representational State Transfer. REST APIs rely on a few guiding principles such as a client-server structure, simple, uniform interfaces to communicate across systems, stateless operations, and more.

  • Webhooks: Webhooks are event-based, and simply put, are automated messages sent from one system to another system anytime an event occurs. Webhooks are even referred to ‘reverse APIs’ as a concept to check for changes in data.

  • SOAP API: SOAP is an acronym for Simple Object Access Protocol. SOAP APIs are more structured and formalized than other APIs, they are reliable and trusted, but can be slower than other APIs. SOAP APIs uses an XML-based messaging protocol which includes the Envelope, Header, and Body tags as required by the endpoint.

  • · GraphQL API: GraphQL is an acronym for Graph Query Language. The Graph Query Language defines how one API asks another API for information and instead of relying on how the server defines the endpoint, a GraphQL query can ask for a specific piece of information. GraphQL was originally created by Facebook as an internal tool in 2012 but they publically released it in 2015 as an open-source language for APIs.

  • WebSocket API: Web Socket APIs rely on the Web Socket computer communications protocol, which is a full-duplex communication channel over a single TCP connection. Compare WebSocket protocol to HTTP (HyperText Transfer Protocol), which is a half-duplex communication. WebSocket APIs provide a standard way for servers to send information and data to clients, even when the client is not requesting data. WebSocket APIs also allow data to be communicated between clients and servers, while keeping connections open.

Postman API Network. The Postman API Network provides a central place for both API consumers and API producers to easily discover, explore, and share APIs.

You can find APIs from many popular providers in the Postman API Network, including the following:

  • Twitter APIs: Twitter APIs allow you to do many different things like looking up specific users, looking up specific tweets, searching for tweets, filtering real-time streams of tweets and much more.

  • Imgur APIs: Imgur APIs expose the entire Imgur infrastructure. In fact, using Imgur’s API, you can do just about anything you can do on imgur.com, like finding and sharing the funniest, most informative and inspiring images, memes, GIFs.

  • Okta APIs: Okta offers a wide range of APIs, including endpoints to authenticate your users, challenge for factors, and recover passwords. Okta also offers ndpoints to configure resources such as users, apps, sessions, and factors.

  • SurveyMonkey APIs: SurveyMonkey APIs makes it possible to explore SurveyMonkey data, including survey questions, survey responses, contacts, benchmark, errors and more.

  • Yelp APIs: Yelp’s Fusion API allows you to get the best local business information and user reviews of more than a million businesses in 32 countries.


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