What Is An API? How It Works & How Developers Use Them

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Rafael Timbó
Rafael Timbó
Chief Technology Officer

Table of Contents

Learn what an API is, how they are used with API integrations, and how to utilize different architectural styles.
Published on
February 23, 2023
Updated on
April 11, 2024

When looking into application development, you will come across various industry-specific concepts, including the term API. APIs and web APIs can be hard to understand for non-tech-minded individuals, but when the concept is broken down, it is easy to understand their roles and how an API is available for them in a software development project.

APIs help with apps, websites, and other software interfaces, and API integrations are the action of integrating an API or service. We'll cover what is an API in software, the use of an API, how they work, allowing developers to access it, and the most popular types of API architectures. 

What is an API?

API stands for application programming interfaces, which are sets of protocols and definitions for creating and integrating application software. API allows your service, product, or app to communicate with other services and products without having to know how they're implemented. This lets you save money and time by simplifying app development. 

For example, the weather app on your phone can use an API to communicate with the weather bureau's software systems, which contain daily weather data. Without access to the API, the weather app wouldn't be able to access daily weather information and display it on your phone or web browser. The file system needs to access files through an API gateway in order to communicate and display the information.

An API integration is a connection between two or more applications that lets those systems exchange data. Many businesses use API integrations to enhance productivity and drive revenue. Facebook Messenger and WhatsApp, for instance, use it to let you communicate with other users with an API key and its user interface. These types of examples of APIs are web APIs, meaning they use web APIs to communicate and are accessed over the World Wide Web via the HTTP protocol.

How Do APIs Work?

Essentially, the API is the middleman between the web server and the application. Like a waiter at a restaurant, it's an intermediary between the kitchen (the web server) and customers (the user). After a customer tells the waiter their order (API call), the waiter will request the order from the kitchen. Once the kitchen has finished the order, the waiter will give the customer what they ordered (API endpoint). 

Different Types of APIs

This can be classified by their scope of use, and the web applications they integrate with. These types are essentially broken down into different groups by the access level and scope of use. There are four widely known different types in the software industry: Open APIs, Partner APIs, Internal APIs, and Composite APIs.

Open API

An Open API is publicly available to tech teams and software engineers. Companies create open APIs to encourage third-party users to share and discover new ways of using their software product(s). The choice for this type is to help share information via an API, use an API to integrate, and is a popular API amongst the API marketplaces.

Here are three well-known examples of open APIs to understand this concept better:

Twitter API's Essential Tier

A user can use Twitter's Essential tier API to tap into core Twitter elements, such as Direct Messages, Tweets, Lists, and Spaces. Twitter wants users to use these more modern web APIs to build products and tools that make Twitter healthier, better, and more capable of extending public conversations.

U.S. Patent Examination Data System API

The U.S. Patent Examination Data System API lets customers fetch and download multiple United States Patent and Trademark Office (USPTO) patent filing statuses or patent applications at no cost. It contains the Public PAIR's bibliographic and published patent term extension and document data tabs from 1981 to now. It also has data going back to 1935. Anyone using the provided API or web interface can access this data. 

GitHub's API
Tech teams and engineers can use the GitHub open REST API to retrieve data, create integrations, and automate workflows. GitHub provides ample documentation for using its API.

Partner API

Partner APIs have strict rules around security, authentication, and authorization. They are only available to certain parties, such as authorized external users. Using this method helps to aid business-to-business partnerships.

Below is a list of examples of a Web API that uses this particular API. 

eBay's APIs
eBay offers a broad range of choices for general commerce that are only available to eBay partners. Approved access who has a unique partner Campaign ID that links their traffic to their partner account. This compensates them for qualifying transactions. 


Some aspects of the Twitter API
Twitter API offers partner tiers, such as Elevated, Elevated+, and Academic Research. Users must apply through the Twitter API website to use these tiers.


Airbnb API

The Airbnb API is another well-established partner API. As of November 2022, Airbnb does not accept new access requests for their API. Airbnb's global team of partner managers will contact prospective partners based on technological strength, business opportunities, and the ability to support shared customers. Accepted can use the Airbnb API to connect booking software to the Airbnb platform. This allows them to import company data to Airbnb, display listings on Airbnb, and receive bookings through the Airbnb website.

Internal API

This type is used by companies internally to drive productivity, add value, and reduce time spent exchanging data between teams. Unlike open and partner, they have no external exposure to an outsider of an organization.

Advantages for Companies Using an Internal API

  • Increased Security
    Internal APIs are not free from security risks and can have problems with authorization and access control. However, internal APIs tend to have fewer risks. That's because if and when security risks arise within an internal API, they can't be exploited by third-party attackers. Companies using internal APIs also don't have to worry about internal security threats expanding to affect customers and partner organizations.

  • Better Interdepartmental Interactions
    Internal APIs allow for streamlined interdepartmental projects that draw on shared resources. This is achieved by detaching data consumption from the underlying data systems accessed by the API.

  • Automation of Existing Tasks
    Companies can use internal APIs to automate existing tasks through simple APIs. Without internal APIs, teams would have to use heavyweight custom code, which often takes a lot of time and money to write.

Composite API

Composite APIs combine several API requests into one API documentation to save data usage and make apps more efficient with their request and response. 

Many use this for software components and applications that are frequently bundled together. A common example is a shopping cart application, which chronologically batches the following API requests into a single API call. This process could look like the following:

  1. Create a customer

  2. Create an order for the customer

  3. Add a product or service to the order

  4. Add another product or service

  5. Change order status

Note that this is not the same as a batch API. Unlike composite APIs, batch APIs do not care about sequential order. 

4 Examples of API Architectural Styles

APIs are usually classified in terms of their software architectures — how clients interact with servers. 

Clients are the people who can use APIs — they make requests to APIs to change something in an application or retrieve information. Servers, on the other hand, are used by the application and contain data that the client wants. Servers have an API that's for interacting with clients without giving them direct access to the data stored on them. 

The following most common types of API architectural styles are best used by someone who has familiarity with a programming language, API strategy, and API testing:

REST Architectural Style

 REST stands for Representational State Transfer, and is a software architectural style that defines rules for creating web services. APIs that follow the REST architectural style are called RESTful APIs. RESTful APIs allow requesting systems to access and manipulate web resources by using a predefined and uniform set of rules. Interactions in REST-based APIs use the web's Hypertext Transfer Protocol (HTTP).

Six architectural guidelines of RESTFul APIs:

  1. Stateless
    Rest APIs use statelessness is when the client is responsible for handling and storing session-related information on their own side. Stateless APIs help scale to millions of concurrent users and make it less complex by removing all back-end state synchronization logic. They are also easier to cache.

  2. Cacheable
    RESTful API is cacheable. The client returns the data from their cache for any subsequent request, removing the need to send the request again to the server. This improves performance for the front end and offers better scalability scope for a server since the load has been minimized.

  3. Layered system
    RESTful APIs consist of many layers. Accordingly, you can deploy APIs on Server A, authenticate requests on Server B, and store data on Server D.

  4. Client-server separation
    This constraint means that server and client applications can evolve separately without depending on one another.

  5. Code on demand
    This optional constraint lets you return executable code to support part of your program.

  6. Uniform interface
    This constraint defines the interface between servers and clients. It decouples and simplifies the architecture, enabling each part to develop independently.

Pros and Cons of Rest API

RESTful APIs provide the following benefits:

  • Extremely scalable, since the server and client are decoupled
  • Easy to use and standardized
  • High performance due to cache abilities
  • Can serialize data in JSON or XML formats

However, they also come with drawbacks, such as:

  • Lack of state — unfortunately, most web apps require stateful mechanisms
  • Lack of security


Remote Procedure Call (RPC) allows users to tap into services in external networks, which are services within programs on other devices. Due to this, RPC APIs can call processes through remote systems.

Besides using the client-server model to communicate with users, RPC APIs also rely on an intermediary link called an interface definition language (IDL) to drive communication between machines using different languages and operating systems.

RPC Pros and Cons

RPC provide various benefits, including:

  • Lightweight payloads, which means high performance
  • Usage of applications in distributed and local environments
  • Ease of use and understanding

Disadvantages include:

  • Lack of standardization and thus more difficult implementation
  • Lack of flexibility for hardware architecture

SOAP Style

Simple Object Access Protocol (SOAP) APIs use SOAP, a lightweight XML-based protocol for exchanging information in distributed and decentralized application environments. Because SOAP APIs are less flexible, they are no longer as popular as they were in the past. 

Other features of SOAP style include:

  • A strongly typed messaging framework that relies heavily on schemas and XML
  • Every input parameter bound to a type and similarly defined
  • Everything codified in the Web Service Description Language (WSDL), an XML-based interface description language that describes a web service's functionality

SOAP Pros and Cons

SOAP provides the following advantages:

  • Platform, language, and transport independence
  • Standardization
  • Built-in error handling
  • Speed
  • Compatibility with distributed enterprise environments
  • Automation when paired with certain language products

It has several disadvantages, including:

  • Only supports bloated XML structures for responses and requests
  • Requires a lot of bandwidth due to the large size of XML files
  • Requires additional effort to remove or add message properties
  • Rigid schema may slow down adoption

For the most part, REST is easier to use and more flexible than SOAP. That's because REST uses smaller formats like JSON, while SOAP uses XML, which can result in bloated files. REST is also faster since it doesn't require extensive processing. 

GraphQL Style

Finally, there's the GraphQL architectural style. Unlike REST APIs, which require several calls to return the needed information, GraphQL makes precise data requests. It does so by using types to ensure that apps only ask possible queries and provide helpful and clear errors. 

To use GraphQL, just send a GraphQL query to your API. You will then get exactly what you want. Due to its precise nature, GraphQL can create fast and stable apps and is a great alternative to Rest API. 

GraphQL Pros and Cons

GraphQL has many pros, such as:

  • Precise data requests
  • Detailed error messages
  • The ability to create fast and stable apps
  • Flexible permissions
  • The ability to fit graph-like data very well
  • Typed schema that makes it easier to discover which queries are available

GraphQL cons are:

  • Performance issues, especially when you have nested fields — this makes REST a better option for complicated requests
  • Steep learning curve
  • Caching complexity, since it doesn't reuse HTTP caching semantics and thus requires custom caching effort

Public API vs. Private API

Now that you know the most common API architectural styles, let's explore the difference between public and private APIs.

Public API

This is just another name for an open API — an API that is publicly available to software developers. As discussed above, this type offers many advantages, including integrated workflows, visibility to specific activities, and cost savings.

This type is generally open to the public, who can hook into the API to create further usage of the particular platform. It creates opportunity for new web applications, and online businesses by tapping into the platform’s available information. An example of this might be an app that helps you manage all of your social media accounts from one place. This type of web API would need to have access to the social media’s Public API in order to connect and get data.

Private API

A private API is another name for an internal API — an API that is used within an organization. Unlike public APIs, they are not intended to be used by consumers or third-party individuals. The primary users of private APIs are in-house software engineers, who use them to reduce development time and enhance productivity.

The main advantage of private APIs is that they're usually safer than their public counterparts. They can also help programmers automate existing tasks and encourage interdepartmental collaboration. A good example of a company that will use a private API is a financial services company, and have to be protective of the information of their customers and company, or they might risk their security.

Why Are APIs Important?

APIs provide many advantages, including integration of software programs, access control, and customer and vendor engagement. 

Software Program Integration

If you want to create software or an app, you need APIs. Otherwise, your software or app won't be able to communicate with other devices or platforms. 

Access Control

APIs can also protect your systems and data. Specifically, API Access Control (ACC) prevents unauthorized access to confidential data by limiting access to specific APIs for different users. Developers can use AAC by:

  • Creating user roles: To use AAC, you must create user roles with your API management console.
  • Setting permissions based on user roles to limit access: For instance, they can allow admin users to view confidential data while restricting other users from seeing that data.
  • Restricting API calls by user role: Devs can use ACC to define varying levels of access to an API. For instance, users who are assigned to the "view data" role can view data through the API, while users assigned to the "create data" role can add new records.

Customer and Vendor Engagement

To attract and retain high-quality leads and customers, you must engage users by improving their user experience; strengthening their relationship with you; and increasing clicks, downloads, and shares. 

One of the best ways to drive engagement is to use first-rate customer and vendor engagement or service APIs. These APIs empower developers to enhance or create applications with engagement functions. Here are examples of companies that leverage an API include:

  • Pendo API: A product experience platform that lets software developers improve user experience, Pendo API integrates user behavior data in dashboards. Developers can use the API to implement segmentation, user experience, feedback, and retroactive analysis.

  • Amazon Pinpoint API: This Amazon Web Service management service provides user behavior insight and spots opportunities for user engagement. Developers can use it to send transactional and targeted messages.

  • GazeCloud API: This groundbreaking API uses users' webcam to track eye movements and create heat maps of where eyes are focused on a given webpage. Use this tool to understand the relationship between user attention and engagement.

Hire API Developers with Revelo

Most software and app developers are familiar with at least one type of API. They may even know how to interpret API server responses, API design, and API specifications. However, that's not enough to make a state-of-the-art piece of software. That's why you should hire top-notch API developers who are experts at doing API development. 

If you're having difficulties finding tech talent that can build an API, Revelo can help. As Latin America's premier tech talent marketplace, we provide access to thousands of developers familiar with how to create an API. Moreover, all of our talent has been rigorously pre-vetted for their English proficiency and technical and soft skills.

Interested in getting MAMAA-caliber API services? Fill in this form to get started, and one of our representatives will meet with you to learn about your company and needs for the role to find the perfect fit. 

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