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 own specific functions, advantages and disadvantages. The three main types include:


Open APIs


Open API


Partner API

It’s important 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 has to be extra vigilant about security, control and misuse . Numerous different 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. The terms of use are usually governed by a negotiated agreement, and partners need to obtain permission and specific access information to use them.


Unlike open APIs, which are generally free and available to the public, partner APIs are monetized. 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 in 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 were 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 are used to 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.

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, designed specifically for web servers and browsers, and it can communicate across a number of different application protocols.


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.

Which APIs are a priority for your business?

Determining which types 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 a challenging process. Our team at Torry Harris Integration Solutions can help. As one of the most trusted advisors to enterprises across the world, 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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