What are the different types of APIs? Here’s what you need to know

Types of APIs

An API, or application programming interface, is a software intermediary that allows two applications to communicate with one another through a set of commands. Once linked, the two applications can access and employ another system’s data and functions. 

This application integration allows you to increase the functionality of your applications without having to reconfigure them yourself. In other words, you borrow instead of build. And, once your systems are integrated, data silos are replaced by seamless workflows of shared data and scalable processes.   

As you can see, APIs are a vital part of doing business, better. To get the most out of your APIs, it’s important to understand which types are best suited to your needs. 

This article provides an overview of the different types of web APIs as well as web service APIs so that you can maximize your API performance. 

Related: Common examples of API integration

Overview on Web APIs 

Web APIs are those that can be accessed over the web using HTTP protocol and are used to extend the functionality of either a web server or web browser. There are four main types of web APIs: 

  • Open or public APIs

These APIs, also called “external,” are publicly available, meaning they’re published on the internet and are designed to be shared. Organizations want third-party developers or partners to be able to easily access and use them to connect to data or services. Thus, there are typically minimal restrictions. 

Open APIs allow companies to innovate and provide better services to their customers. Take digital banking, for instance. Using open APIs, a financial institution can share its customer data with FinTech firms to develop personal finance management applications such as a budget management app. As a result, the FinTech firm gets access to rich data, the customer gets a helpful budgeting tool, and the financial institution has higher customer satisfaction. 

  • Partner APIs

Partner APIs are essentially open APIs in terms of design, but they can only be accessed by third-parties with exclusive permissions or licenses. These APIs are typically used to sustain a specific and strategic business-to-business partnership and often feature in a software as a system (SaaS) ecosystem.

A use case for a partner API is the app Checkr, which allows companies to perform background checks on employees and contractors through a third-party. This gives the company confidence in the veracity of the report while saving them the considerable time and expertise it would take to do the work themselves. 

  • Internal or private APIs

Internal APIs are used within an organization to share resources or enable functionality between services. In contrast to open APIs, they’re hidden from external consumers and only the developers within the organization have access. Often, these APIs improve productivity across business lines, efficiency of workflows, and the overall agility of the enterprise. 

Just one example of an internal API at work is in the case of provisioning for new employees. During the onboarding process, HR can easily share new employee records with IT in order to set up permissions and grant access to the company’s systems and applications. 

Related: A guide to API integration

  • Composite APIs

This type of API is actually a sequence of tasks that batch different data and service API requests into a single call. These APIs facilitate the speed and performance of a multi-endpoint request.

Composite APIs are used often in microservice architectures in which a single task might require data from multiple applications. 

Now that we’ve covered the types of web APIs, we can take a look at the various architectural styles used to construct them. 

Web service APIs 

An API’s architecture indicates the constraints by which it operates and, therefore, the situations to which it’s best suited. Here are four common web service APIs and their basic architectures:

  • REST

REST, or representational state transfer, APIs are widely used. A REST is a set of design principles, not a specific protocol, and it is these principles that define it. All REST APIs adhere to the following architectural constraints: a decoupled client/server, statelessness, are cacheable, have a uniform interface, and operate as a layered system. REST APIs are highly flexible and can utilize a variety of data formats.    

  • SOAP

SOAP (simple object access protocol) is a commonly used web protocol that uses the XML format to define the structure of the data transfer and methods of communication between applications. Most developers prefer REST over SOAP, though SOAP is well suited to on-premises scenarios. 


RPC stands for remote procedural call protocol, which is used when a call sends multiple parameters but receives just one response. JSON-RPC uses the JSON format to transfer data. RPCs often require close coupling between the API client and server, which can result in a difficult-to-manage API ecosystem. 


XML-RPC protocol is similar to JSON-RPC, but it uses XML format to transfer data. The SOAP protocol also uses XML, but is a proprietary format. XML-RPC is a good option when you need to connect multiple computing environments without sharing complex data structures directly. 

Related: The benefits of API management 

Workato, the leader in integration-led automation, allows you to manage the full lifecycle of your APIs, whether they’re for internal teams or external partners. You can learn more about using Workato to manage your APIs by scheduling a demo with an automation expert.