As more businesses expand their digital footprint, popular APIs have become essential tools for growth. Today, APIs are used for countless purposes, from integrating payment gateways and enabling social logins to powering IoT devices and AI-driven platforms. The ability to use the API effectively defines how well companies can innovate and stay competitive. Modern API architecture now includes REST APIs, GraphQL APIs, and RPC APIs to cover a wide range of integration needs.

Because APIs offer so much flexibility, the challenge isn’t just building them but ensuring they serve the right API consumers: developers, partners, and even AI agents, who rely on them daily. This guide breaks down the most common types of APIs so you can navigate the API ecosystem with confidence and understand where they fit in your business strategy.

What Is an API?

APIs, or Application Programming Interfaces, are powerful tools that serve as a connector responsible for requesting, interpreting, and delivering information between the client (the application) and the server (the database). Every API request interacts with an API endpoint, making it possible to deliver consistent and reliable API services across platforms. Whenever you run a quick Google search, browse your LinkedIn feed, or send money via your banking app, you interact with APIs - they are truly ubiquitous.

The most common and simplest way to think of an API is using the example of a server at a restaurant since they have parallel responsibilities, taking orders from customers (the client) and delivering them to the kitchen (the database).

If you want to learn more about the basics of how APIs work, read this guide.

Why API Portals Are So Important to the Success of Your API Program

Unless you have only a few APIs that are all the same and used by the same type of end-user, you need an API portal - a user-friendly platform that helps developers, business units, and partners consume your APIs in an accessible way - to run a successful API program.

API portals centralize your API assets in one place, increasing adoption rates and promoting innovation. They also simplify connections with API gateways, which act as a central entry point for API services.

With the growing usage of APIs by non-IT people, from data analysts to citizen developers, gateways and management tools do not provide the infrastructure to start and grow an ecosystem needed to ensure the success of your API project.

API portals bridge that gap by providing developers and non-technical users alike with the tools they need to use your APIs easily.

Apiboost API portal can help you confidently navigate the API world and alleviate the work needed to manage your products.

Different Types of APIs: The Four Types of APIs and Their Use

Not every popular API must be built the same way or for the same purpose. 

Even though every application and business has different needs, APIs also can be categorized into four main types: public, partner, internal, and composite. Regardless of type, all of them rely on well-structured API architecture to ensure scalability and maintainability.

Let's break down each of them in greater detail.

Four types of web APIs

There are several different types of APIs:

• Public

• Partner

• Internal

• Composite

1. Public APIs

Public, or open APIs, are available for any outside business unit or developer to use.

Companies develop public APIs to share data and applications with other businesses, developers, and non-technical users. 

Many features of these APIs may be freely available, like when a government agency or educational institutions use them to provide access to data they are obligated to share. With registration or the use of an API key, businesses often seek to monetize their public APIs in some way (i.e., limiting usage, offering premium features, etc.).

Google Workspace, Dropbox, and Coinbase are examples of this type.

2. Partner APIs

Partner APIs allow collaboration between different businesses, creating the infrastructure for organizations to integrate their API products into each other's ecosystems. Creating effective data sharing through APIs helps business partners solve complex logistic issues, innovate technology between organizations, and create white label solutions to create new revenue lines.

While some facilitate business between two companies, others are intended to expand business opportunities for one or both companies involved. Ridesharing apps like Uber and Lyft leverage them to collect real-time traffic data, improving their product offering and growing their business as a result.

In the fintech community, innovation often results in entirely new products. The list of how businesses are using APIs to connect is growing by the day, and that pace is only accelerating.

Since it’s not uncommon for partner APIs to operate with sensitive user data, they require more robust authentication, authorization, and security measures.

3. Internal APIs

Hidden from the public eye, internal (or private) API design is made exclusively for internal company use, helping businesses develop better products and services. Internal APIs, when managed well, play a critical role for enterprise organizations that may want to inspire innovation across regions, brands, and departments.

Internal API provides a company's developers and other employees access to corporate API assets which facilitate data sharing that can help businesses operate more efficiently by avoiding business silos.

The most common issues that many organizations face are the adoption of multiple APIs to access the same data and the lack of documentation around those APIs, leading to time wasted for incomplete data sets. Since these APIs are intended for internal use only, authentication and security measures are typically limited, but this is certainly not to say it should be overlooked. 

Since they are usually innovated in a staging environment, good governance can then be applied to push the API to production environments for implementation or external publishing in an API portal.

4. Composite APIs

Composite APIs (also known as an API product) combine two or more data and service APIs. This design allows batching or sequencing to carry out a series of dependent API calls in a single request. APIs are often bundled for partner agreements, and once live, function similarly to the Partner API described earlier. This model requires comprehensive documentation and instructions on the sequential use of the APIs - so there is a heavier lift from the technical side to bring them to life.

While this type of API can be public, internal, or for a partner or customer - the most common instance of an API bundle can be seen when combining multiple data sources required for a sequential API program.

For example, creating a shopping cart API requires several different endpoints to fulfill the order (i.e., create a customer, create an order, add an item, add an item, etc.).

Instead of requesting this information independently, a composite API passes all the data at the end of the sequence – eliminating the need to get and deploy multiple API keys and reducing the upkeep when a single API is updated or modified.

→ Read more: 5 Best API Management Tools for 2025 and Beyond

The Three Main Types of APIs by Purpose

Now that you have a better understanding of what APIs are and how they are structured, it's essential to understand how they will be used by an enterprise, or in other words, what is their purpose?

The demand for an API arises from the increasing interdependence of APIs. Instead of building applications from scratch, companies rely on third-party APIs to reduce time-to-market and improve the functionalities of their solutions.

Mulesoft's API-led connectivity approach categorizes APIs into three main categories to help organizations better understand how to manage their API assets.

• System APIs: The purpose of a system API is to pull data from an existing system integrated within an organization.

• Process APIs: This type of API orchestrates the interactions and merging of data within a single system or across multiple systems. These APIs allow enterprises to combine data across multiple systems for a specific business purpose.

• Experience APIs: An Experience API collects the data unlocked via the system and process APIs and exposes it to a target audience via the client.

With comprehensive API accounting for 83% of all web traffic, businesses need to accelerate digital transformation to keep up with the competition.

Different Types of API Protocols & Architecture

Building your API using the protocols and architectural styles (the rules and structures that govern an API) best suited for your API needs is critical to ensure high performance.

Here are some of the most common ones, serving different purposes.

1. REST APIs

Representational State Transfer (REST) is the most popular architectural style for building modern APIs.

For an API to be considered RESTful, it must satisfy the following requirements: 

• Uniform Interface (UI): No matter where API calls may come from, they should be identical when requesting access to the same resource.

• The Client-server Model: the client and the server should be separated entirely and interact only through an API.

• Statelessness: Request should contain all the information needed for executing a given task without relying on any context on the server.

• Caching: An emphasis on storing reusable resources to optimize performance and improve scalability.

• The Layered System: REST API is made of multiple layers, each responsible solely for performing one core functionality. For instance, a three-layer architecture most common for them can be broken down into the data access, business logic, and presentation layers.

• Code on demand: This means that developers can drastically expand the functionality of their REST APIs by including executable code in their existing API calls.

The benefits of REST APIs are flexibility in development and implementation, the ability to incorporate popular data formats, and increased scalability when using an API.

2. SOAP APIs

The World Wide Web Consortium develops Simple Object Access Protocol (SOAP) to empower developers to build APIs using primarily Web Service Description Language (WSDL), an XML-based definition language, for describing the functionality of a SOAP-based web service.

Unlike the flexible REST architecture, where the central premise is the null style (meaning that you start with no constraints and gradually create and stack them on top of each other as you build your API), SOAP is defined by a rigid set of rules and standards to create reliable and secure APIs.

The advantages of SOAP include the ability to support a variety of web-based communication protocols (HTTP, SMTP, TCP), a solid and reliable foundation for an enterprise's resources, security, and built-in error handling.

3. GraphQL API Type

GraphQL is a modern query language for APIs developed by Facebook in 2012 and now maintained by the GraphQL Foundation. Unlike REST or SOAP, which often require multiple calls to different endpoints, GraphQL lets clients request exactly the data they need in a single query. This reduces over-fetching and under-fetching of information, improving performance and efficiency.

GraphQL works with a strongly typed schema that defines how data is structured and what queries are possible. It is widely adopted for building flexible, client-driven applications and is especially common in environments where front-end teams need precise control over the data powering web and mobile experiences.

Make Your API Work For You: API Portals as Powerful API Management Tools

Unless you have only a few APIs that are all the same and used by the same type of end-user, you need an API portal - a user-friendly platform that helps developers, business units, and partners consume your APIs in an accessible way - to run a successful API program.

API portals centralize your assets in one place, increasing adoption rates and promoting innovation.

With the growing usage of APIs by non-IT people, from data analysts to citizen developers, gateways and management tools do not provide the infrastructure to start and grow an ecosystem needed to ensure the success of your API project.

API portals bridge that gap by providing developers and non-technical users alike with the tools they need to use your APIs easily. With proper governance, businesses can streamline API services, monitor API requests, and ensure every API endpoint remains secure and accessible.

Apiboost can help you confidently navigate the API world and alleviate the work needed to manage your products.

We specialize in developing portals, allowing you to focus on creating API products to build additional revenue streams for your business and drive up adoption rates =among developers and non-technical users alike.

Do you want to learn more? Reach out to our team today to schedule a free consultation.