What Is an API: Understanding How They Work
Rafael Timbó

What Is an API: Understanding How They Work

Learn what an API is, why you should know what it is, and how they are used with API integrations.
Published on
February 23, 2023
Updated on
March 13, 2023

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When hiring qualified programmers for projects, you'll come across various industry-specific concepts, including the term API. APIs can be hard to understand for non-developers. When you're first introduced to the term, you may be left with questions such as:

  • What does API stand for?
  • What is an API in programming?
  • What is an API used for?
  • What is an API integration?

Read this guide to learn more about APIs and API integrations. We'll cover what is an API in software, what APIs stand for, how they work, types of APIs, and the most common APIs architectural styles. We will also discuss the differences between public and private APIs and whether you need developers who are familiar with architectural API styles.

What is an API?

API stands for application programming interfaces, which are sets of protocols and definitions for creating and integrating application software. They let your service, product, or app 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 uses APIs to communicate with the weather bureau's software systems, which contain daily weather data. Without an API, the weather app wouldn't be able to access daily weather information and display it on your phone.

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 APIs to let you communicate with other users.

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.

Types of APIs

APIs can be classified by their scope of use. Here are the most common types of APIs:

Open API

Also called public APIs, open APIs are publicly available to software developers. Companies create open APIs to encourage third-party developers to share and discover new ways of using their software product(s). Well-known examples of open APIs include:

  • Twitter API's Essential tier: Developers can use Twitter's Essential tier API to tap into core Twitter elements, such as Direct Messages, Tweets, Lists, and Spaces. Twitter wants developers to use this API to build products and tools that make Twitter healthier, better, and more capable of extending public conversations.
  • U.S. Patent Examination Data System API: This 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 REST API: Developers can use the GitHub open REST API to retrieve data, create integrations, and automate workflows. GitHub provides ample documentation for using its REST API.

Partner API

Partner APIs have strict rules around security, authentication, and authorization. They are only available to certain parties, such as authorized external developers. Developers usually use these APIs to aid business-to-business partnerships.

Some of the most popular APIs are partner APIs. Examples include:

  • eBay's APIs: eBay offers a broad range of APIs for general commerce that are only available to eBay partners. Approved developers have 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. Developers 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 developers 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

Internal APIs are used by companies internally to drive productivity, add value, and reduce time spent exchanging data between teams. Unlike open and partner APIs, they have no external exposure to developers or monetization.

Internal APIs provide companies with the following advantages:

  • Increased security: Internal APIs are not free from security risks. Like all programs, they often 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 internal APIs, they can't be exploited by third-party attackers. Companies using internal APIs also don't have to worry about internal API 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

These APIs combine several API requests into one API call to save data usage and make apps more efficient.

Many developers use composite APIs for 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:

  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 composite APIs are not batch APIs. Unlike composite APIs, batch APIs do not care about sequential order.

Most Common APIs Architectural Styles

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

Clients are the program or people using the API — 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 APIs for interacting with clients without giving them direct access to the data stored on them.

Here are the most common types of API architectural styles:

REST Architectural Style

Representational State Transfer (REST) 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).

RESTtful APIs have six architectural constraints:

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

RESTful Pros and Cons

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

RPC Style

Remote Procedure Call (RPC) APIs allow 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 APIs 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.

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 make it easier to discover which queries are available

Its 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

What Is the Difference Between Public & Private APIs?

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

Public API

A public API is just another name for an open API — an API that is publicly available to software developers. As discussed above, public APIs offer many advantages, including:

  • Integrated workflows
  • Visibility to specific activities
  • Cost savings

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 developers. The primary users of private APIs are in-house developers, 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.

Importance of APIs

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

Integration of Software Programs

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. Popular examples of engagement APIs 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 and use tools like REST API Client Code Generator and API gateways. 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 familiar with several architectural API styles.

If you're having difficulties locating API talent, Revelo can help. As Latin America's premier tech talent marketplace, we provide access to thousands of developers familiar with architectural API styles. 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. We'll send you a list of the best API development hires within three days.

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Full-Stack developer with 6 years of experience working with MERN stack. Worked for multiple transnational companies focused on web and cloud, technology services, and R&D. Major professional experience in Frontend with Javascript, Node.js, React.js, and Vue.js

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