APIs are an essential piece of software that tie numerous departments, functions, teams, consumers, and enterprises together. There are a number of different types of APIs, however, each with its specific functions, advantages, and disadvantages. The four main types include:


Public API


Private API


Partner API


Composite API

It’s essential to understand how each of the different types of APIs operate to better know which one makes the most sense for your business needs and circumstances.

What is an API?

An application programming interface (API) is a software intermediary that enables different applications, systems or IoT devices to exchange data and communicate with each other without human intervention. APIs are essential for numerous business functions in the current digital economy, but they don’t work unless they are properly integrated with other APIs they’re designed to interact with.

Integration allows APIs to share data in real-time, helping end-users save time and money while ensuring shared data is consistent, timely, and accurate.

The different types of API

Public API

Also known as open API, a public API is designed specifically for consumption by a market of web-based software developers. While public APIs can be built in a number of different ways, it's critical that they’re easily consumable and accessible by a wide range of people.


Although they’re available to the public, open APIs are still proprietary. For some companies — particularly technology startups that are still trying to carve out a niche in the market — publishing open APIs might encourage other third-party companies to use their products to innovate.


The main disadvantage associated with these types is that their public use and access means the host enterprise must be extra vigilant about security, control, and misuse. Numerous issues could arise that affect customer satisfaction, and these APIs could be more vulnerable to security incidents from malicious actors.

Partner API

The partner API function is similar to open APIs, except it is designed specifically for partner enterprises to fulfill a unique business need. A negotiated agreement usually governs the terms of use, and partners need to obtain permission and specific access information to use them.


Partner APIs are monetized, unlike open APIs, which are generally free and available to the public. As part of the terms of agreement, both the host and partner enterprise will negotiate a pricing model for access to the APIs. (These are usually either individual, bundled or subscription payments.) Partner APIs enable enterprises to develop closer business relationships with their partners while at the same time opening new streams of revenue.


Partner APIs are more focused on their capabilities, meaning they aren’t as easily transferable to enterprises other than the ones they were initially designed for. That can severely limit the profit gains over time if too many resources are expended to develop the API.

Private API

Private APIs are developed exclusively for use by an organization’s own internal development teams. They are designed to streamline challenges specific to the organization and, therefore, should be built with the needs of the internal development team in mind.


Private APIs help integrate a company’s internal IT systems and enable developers to more easily roll out new apps and other tech. While these products may be designed for public use, the internal API remains exclusive to the organization. Private APIs can help significantly minimize operational redundancies and increase productivity.


Even though private APIs are, by their nature, internal, there are a number of security challenges they create. They often still interact with client-facing APIs at other enterprises, creating vulnerabilities. Host enterprises need to ensure that each internal API is properly protected against cybersecurity threats.

Composite API

A composite API enables users to request data from multiple servers and sources and complete requests through a single API call. Composite APIs are generally used to undertake complex tasks that require more than one API, creating a simpler and more seamless user experience.


Composite APIs are generally preferred by organizations with a large, interdependent ecosystem of APIs, as well as those with business functions that require access to more than one resource to complete. In addition to providing the capacities to optimize performance, composite APIs also simplify processes and enable more efficient functionality.


Because composite APIs are generally used to reduce complexity and accelerate processing times, they are generally most applicable to organizations with extremely diverse web application infrastructures. Building, developing and deploying APIs can be a resource-intensive process, and adding a composite API layer could be disadvantageous for organizations operating simpler API ecosystems.

In addition to the four main types of API, less common ones include:

Each of the above types of API are considered web APIs, meaning they access, share and exchange information using the web. By contrast, remote APIs are used to access information located in a resource that is separate (or remote) from the device making the initial API request. Even though remote APIs are considered a distinct category, most remote APIs are classified as web APIs because API communication today primarily takes place over the internet.

API protocol types

API protocols define the rules by which APIs can communicate and integrate with other systems or devices. There are three main formatting types, including:


Representational state transfer (REST) architecture is among the most popular API protocol formats. REST consists of a client-server architecture that is stateless, meaning client information doesn’t get stored anywhere. Because it is separated from both the back and front end, REST gives extra flexibility throughout the development of the API.



Remote procedural call (RPC) protocols differ from REST in that they encode data to complete actionable requests, as opposed to simply exchanging information between different endpoints. RPC uses either XML or JSON language to function (it can be further broken down into RPC-XML and RPC-JSON).



Simple object access protocol (SOAP) is perhaps the most extensive of the three main API protocols. SOAP is used to create a web API specifically designed for web servers and browsers, and it can communicate across a number of different application protocols.



This type of API uses Hypertext transfer protocol (HTTP) to communicate between different applications and systems. HTTP APIs can be used to create a RESTful API (another name for REST APIs) at a low cost, using cloud computing services like AWS.

Protocol Buffers – Protobuf, or Protocol Buffers, is a data serialization mechanism invented by Google, which allows data to be encoded in compact binary format instead of XML or JSON. The advantage of using a binary format is performance, as API infrastructure can handle more traffic within a given time window as it optimizes data transport over the network. gRPC defines an interface specification language and is based on protocol buffers.

These protocols, by default, assume synchronous communication between the API requester and the responder. There are additional specifications for asynchronous communication, such as Webhooks, AsyncAPI, etc., which will be the focus of our next blog.

The importance of API integration

There are thousands of APIs available to the modern API consumer, and most organizations have numerous different types in their IT environment. The larger the API ecosystem, the more difficult it is to maintain visibility over each individual application, possibly limiting an organization’s ability to derive the expected value from its APIs.

That’s why it’s important for business leaders to invest in an API integration platform. An API platform helps organizations connect all of the APIs in their entire ecosystem to enhance functionality, increase efficiency, and make them better equipped to adapt to changing market demands. Ultimately, the right API management tool helps organizations maximize the value of their APIs so they can bring new products and services to market faster and enhance customer satisfaction.

Which APIs are a priority for your business?

Determining which type of APIs help meet your current business priorities requires a comprehensive assessment of your systems, processes, customers, and objectives. This is the prerequisite for forming a comprehensive API strategy, which you’ll need before you begin developing APIs.

Through the evaluation of your business, you should identify gaps and opportunities that could be substantially addressed by building and deploying APIs. You should also consider your customers’ needs as the market changes and develops. You can identify new business opportunities that will inform the development of APIs to solve customer problems.

Determining what kind of APIs are the right move for your business is challenging. Our team at Torry Harris Integration Solutions can help. As one of the most trusted advisors to enterprises worldwide, we work with your team to help you leverage the power of digital access through integration.

Contact us today to get started.


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