What is an API?

An API, or an Application Programming Interface, is the backbone of modern digital experiences and interconnected devices. APIs help facilitate seamless communication between software systems and applications, helping them exchange data and access functionality.

Benefits of APIs

APIs are used in myriad ways in applications we all use every day.  It would be impossible to do online banking, use a mobile app, or, in some cases, even start our cars without APIs. Anywhere two systems need to communicate, APIs are usually the way to do it.

For example, online stores use APIs to link with ecommerce payment systems, letting customers make safe payments without leaving sites. APIs bring real-time conditions from weather providers to mobile devices. Websites often use APIs to suggest related (“you may also enjoy”) content recommendations for readers browsing articles and pages.  

Increasingly, APIs are central to the way we interact with the physical as well as virtual world. Connected Internet of Things (IoT) devices collect vast amounts of data, which can be processed, analyzed, and used in a multitude of ways. APIs provide the means for IoT devices to communicate this data to other systems, facilitating actions like remote monitoring and control.

How APIs work

APIs define the way one system makes requests to another. While different types of APIs work slightly differently (see below), all APIs involve some sort of function call from one system to the other. This call will happen over a commonly understood protocol, typically HTTP in modern web services.  

An API is basically a definition of what functions a system will respond to, what inputs it needs to construct the response, and what outputs it will offer. When a client (the system making a request) calls the server (the system that responds to the request), it calls one of the provided functions with the necessary inputs. The server then processes the request, validating that it is properly constructed and that the client has necessary authorization to make the request. If everything checks out, it will respond back.

APIs have their own terminology for many of these items.

API components

Endpoints refer to the specific URLs or routes that are exposed by the API to allow clients to interact with it. These endpoints define the different operations or actions that can be performed on the API, such as retrieving data, creating new resources, updating existing resources, or deleting resources.

Headers play a crucial role in API requests and responses as they contain metadata related to the request and response. They’re also essential in ensuring the accurate transmission of information and the smooth functioning of the API, including necessary client authentication details for the requested resource.

Parameters are variables passed along with an API request to provide additional information or modify the behavior of the request. These parameters can be used to filter, sort, paginate, or customize the response from the API, allowing clients to retrieve specific data or perform specific actions

Types of APIs

APIs aren’t new. In fact, they’ve gone through decades of evolution. Remote Procedure Calls (RPC) date back to the 1970s and are still in use today. 

By the 2000s, the popularity of RPC waned in favor of Simple Object Access Protocol (SOAP). SOAP, in turn, was largely supplanted by Representational State Transfer (REST), which, unlike SOAP, was stateless and tended to be less “chatty,” enabling more modern and higher-scale applications.

Today, among the most prevalent types of APIs are REST APIs and GraphQL. Below, we explain the functionality of each and their key differences.


One of the first types of web service APIs, SOAP is a secure way to build APIs. SOAP APIs help exchange information securely between systems and applications, for example, facilitating bank transfers between branches. 

SOAP works by encoding data in the XML format. As noted, it’s an older, established API protocol, and can be slower and more complicated than API architectural styles like REST.


REST APIs adhere to the REST architectural style. They use a resource-based approach where each resource is identified by a unique URL. 

REST APIs use HTTP, the same protocol that powers websites to communicate with and access server data. Clients can use standard methods like GET, PUT and DELETE to access and manipulate data on the backend.

Their widespread adoption stems from their simplicity, flexibility, and support across various programming languages and platforms. However, REST APIs can be verbose and require multiple requests to fetch related data.


GraphQL, an alternative to REST APIs, empowers developers with greater flexibility and control over data fetching. Unlike REST APIs, which provide predefined data structures, GraphQL allows clients to specify the exact data they require through a query language. 

This approach optimizes data transfer, reducing unnecessary network traffic and enhancing performance. GraphQL’s adaptability makes it particularly suitable for complex data retrieval scenarios and applications with intricate data relationships.

APIs in composable architecture

One way APIs are increasingly being used is to build more differentiated digital experiences that pull data and content from a multitude of different systems at the front end. 

Commonly called composable systems, they use APIs to access backend services such as content management systems (CMS), ecommerce systems, marketing automation platforms, digital asset management (DAM), product information management (PIM), customer data platforms (CDPs), customer service systems, and other applications. 

No two composable experiences are the same, which is why APIs are so important. They act as the conduit to backend information, enabling each business to build the right experience for their unique needs.

Furthermore, APIs are also crucial to enabling omnichannel experiences. By leveraging APIs, businesses can easily deliver content and functionality through emerging channels, such as mobile apps, IoT devices, and custom user interfaces.

API integration challenges

Integrating APIs into software applications is important as it allows applications to leverage the functionality and data of other systems, enabling seamless communication and collaboration between different software components.

This integration brings benefits such as increased efficiency, scalability, and the ability to access a wide range of services and resources, ultimately enhancing the functionality and user experience of the software application.

Integrating a single API is often not too difficult for a developer, provided that API is straightforward, performant, and well documented. The challenges of API integration in software applications include dealing with varying API designs, versioning issues, authentication and security concerns, and ensuring compatibility and stability between different systems.

As more APIs become part of an overall system architecture, managing the idiosyncrasies of all the APIs while ensuring good performance can place a considerable burden on developers

Minimizing API sprawl with API Mesh

Managing APIs that power composable experiences can become a challenge

While using one API can be simple and straightforward, integrating and managing a whole series makes development work increasingly taxing for engineers, who must ensure optimal performance for each one.

This requires middleware to manage connectivity to all APIs, ensure performance, handle retry logic, transform and assemble data, enable caching and indexing, and much else. 

For developers, API Mesh architecture simplifies the complexity of managing multiple APIs by abstracting the underlying services and presenting them as a single cohesive interface.

WordPress VIP and APIs

WordPress VIP is a popular CMS for use with API-driven architectures. It provides a multitude of APIs. For example:

  • Block Data API plugin—provides clean, easy-to-use data via both REST and GraphQL. 
  • WordPress REST API—lets developers programmatically manage the content of the site’s content blocks. 
  • WPGraphQL—provides a widely used GraphQL option to access block content.
  • VIP Cache Personalization API—customizes the default caching behavior of the WordPress VIP CDN.
  • Content Recommendations API—helps readers discover content that’s similar to a given article on a website.
  • VIP API Mesh—takes the hassle out of integrating backend systems, accelerating development.

Overall, this architectural approach enhances flexibility and scalability for developers, allowing businesses to reach a wider audience and provide seamless experiences across multiple platforms.