4 Types Of APIs: How They Work And What You Need To Know

Have you ever wondered what an API is? There is a good chance that you have heard of it, but do you know what it means? It is called an application programming interface because it makes data and/or functionality of one website available to other applications through code.

You will learn about what is APIs (application programming interface), APIs Marketing Power, and 4 main Types Of APIs.

What are APIs?

An API provides a powerful and flexible way of connecting different software applications and systems. APIs let a wide range of software products interact with and integrate with one another. APIs also enable developers to extend software’s features and functionality by utilizing the APIs of other developers.

Modern software ecosystems rely heavily on APIs. APIs play a central role in the integration of diverse web applications since they offer virtually unlimited ways to connect them. It makes sense to know how APIs work if you want to integrate your app or service with the digital world.

You should know that APIs can vary from software integration to software integration – therefore, not every API can be the same. APIs are divided into different categories according to protocol, function, and level of access.

Selecting the right type of API will ensure that your company’s API(s) work as you want them to. APIs that share data with the public might be constructed differently than APIs that are meant only for internal use by your employees.

Marketing technology & APIs

To execute creative branding tasks, marketers use a number of different kinds of technologies – a content management system (CMS) for websites, a digital asset management system (DAM) for managing digital assets and creating content, marketing automation platforms for all kinds of campaigns, etc. Many organizations have 20-30 different technology applications within their stack (or more).

Regardless of how many platforms we use daily, what we really need from every single one of them is to be able to accomplish our goals – and without having to figure out how they function. It is fundamental to make people forget we are using technology to produce the contents and to accomplish the tasks we were hired to do.

APIs are at the core of the technology we leverage – so that different platforms can connect to one another and therefore synergize. APIs allow us to create one holistic solution with the functionality of 20-30 different products instead of using 20-30 different technologies.

What are the different types of APIs?

There is widespread acceptance and use of APIs for web applications. Typically, web-based applications use one of four types of APIs: public, partner, private or composite. Specifically, API types determine the scope of use that’s intended.

Types of APIs

Public APIs

A public API, also known as an open API or an external API, is available to any developer. Since open APIs typically have few authentication and authorization measures, the assets they may share are also often limited. In contrast, to open APIs, which are often free to use, other APIs require payment to use, often tied based on the number of API calls.

One of the most advantageous aspects of making APIs public is that data can be shared openly. As a result, any third-party app or developer can integrate with the application that owns the API, increasing the value of the API as well as that of the third-party app. Because the open API lacks restrictions and is easy to implement, third parties can take advantage of the data it provides immediately.

Partner APIs

Partners APIs may be shared externally, but they are only shared with clients with a business relationship with the API provider. Security measures tend to be stronger on partner APIs than on public APIs since access is restricted to clients with official licenses.

APIs are popular with some companies because they want (1) greater control over how their resources are used and (2) greater control over who can access them. Pinterest, for instance, uses a submission-based approach for providing access to new data services via the API, requiring partners to submit a detailed request for how they will use the API to gain access.

Internal APIs

Private APIs (also known as internal APIs) are not intended for use by third parties, unlike open APIs and partner APIs. Internal APIs allow users to transfer data among teams and systems within a company and are only made available within that company. Developers working for the company can access the APIs, but external developers cannot.

APIs are often completely hidden from the public because they aren’t documented in software development kits (or at all) released publicly. Nevertheless, many companies eventually make their internal APIs public.

APIs are preferred for internal data transfers since they are efficient, secure, and traceable. Furthermore, the API allows businesses to integrate new internal systems with existing ones.

Composite APIs

Composite APIs combine multiple APIs to give developers a unified response from a variety of servers by combining requests or calls. A composite API allows you to access data from multiple applications or data sources. As an alternative, you can use a composite API to trigger an automatic chain of calls and responses without requiring your intervention.

In addition to reducing the number of API calls, composite APIs can also result in faster systems because they reduce the number of API calls. These are often deployed as microservices, where one job may refer to a number of internal APIs.

For example, let’s say you want to place an order through the API of a shopping cart. The procedure requires only one request, you might think. However, there are several requests to be made. To begin, you must create a profile for the customer. 

Create the order, add the item, add another, and change the order status after you have completed the previous steps. With a composite API, you don’t have to make five separate API calls in succession.

Types of APIs Architectures

Similarly, APIs can be understood as architectural components. An API’s architecture explains which information it can give clients and how it shares the data. Let’s break down the most prevalent API architectures used today – REST, SOAP, and RPC.

Types of APIS


Almost all web APIs are built with REST today. A REST API is an open-source project that provides scalable, lightweight, and easy-to-use API guidelines. This API (also known as a “RESTful” API) follows the REST guidelines and transfers data from the server to the requesting client.

The following guidelines are briefly summarized:

  • Uniform Interface. In order to ensure compatibility between any client and any server, requests and responses must use HTTP as a communication protocol and be formatted in a specific manner. Responses to server requests are formatted as JSON Object Notation (JSON).
  • Client-Server Separation. All interactions between a client and server must take the form of a client request and a server response. The server cannot request and the client cannot respond.
  • Stateless. Interactions between clients and servers are independent. Client requests are not stored on the server, and past interactions are not remembered.
  • Layered system. Even when passing through intermediary servers between the client and API, requests and responses must always be formatted the same way.
  • Cacheable. It is expected that the server will inform the client whether it can cache any provided resources and for how long it can do so.

Using these guidelines, REST APIs allow developers to make secure, quick, and easy data transfers.


An API can be constructed using SOAP (Simple Object Access Protocol), which is a protocol used to transmit data over networks. Information is encoded using XML using the SOAP protocol, which is standardized by the World Wide Web Consortium (W3C).

As part of SOAP, messages are specifically defined in terms of how and what they should contain.

 Because SOAP APIs follow rigid guidelines as opposed to REST APIs, they are perhaps more secure, though their more extensive coding makes them harder to implement in general.

This is why SOAP is typically utilized for data transfer within an organization that requires high security, while the more flexible REST architecture is used for external data transfers. Additionally, SOAP works on any communication protocol (not just HTTP, as it is for REST).


In regard to the three architectures, the RPC (Remote Procedural Call) protocol is the simplest to understand. By comparison to REST and SOAP, which allow data to be transferred, RPC APIs initiate processes. Scripts are executed on servers.

The call to an RPC API may be performed via either JSON (a JSON-RPC protocol) or XML (an XML-RPC protocol). There are many similarities between XML and JSON, but XML is more secure and more accommodating. Despite its strictness, RPC is an easy and straightforward way to execute code over a remote network.

You probably won’t see RPC APIs on the web as often as REST or SOAP APIs since they have limited security and capabilities. Nevertheless, it can be used to make basic process requests, especially many at once, for internal systems.


This is an excellent overview of APIs, not for the technical-minded developer, but for the average person with an interest in how they work. When you use the right API, you’ll expand your reach and influence by partnering with other applications. It is important to choose the best types of APIs for your business that suit your needs and one that you can afford.

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