What are the types of APIs and their differences?

Last updated on May 29th, 2023

An API is an effective and flexible way to connect disparate software programs. APIs enable a wide range of software products that are not related to interoperate and integrate with each other and data. Developers can also add features and functionality using APIs from other developers. A wide variety of APIs is essential for today’s enterprise, mobile, and web software.

APIs may not be the same. Developers have the option to work with a variety of API types, protocols, and architectures that best suit different businesses and applications.

Table of Contents

There are four types of web APIs

APIs can be used in web applications and are widely accepted. There are four types of APIs that are commonly used in web services. They can be public, private, mixed, and partner. The API “type” is used to indicate the intended use.

1. Public APIs.

Any outside developer can access the API. A public API is available to any business that has a business strategy that includes sharing data and applications with other businesses. These APIs are also known as open APIs and external APIs.

Most public APIs require authorization and moderate authentication. A per-call fee may be imposed by an enterprise to make the API more profitable.

2. Partner APIs.

This API is only available to a select group of API users or developers outside the company. It facilitates business-to-business interactions. A partner API allows a business to connect its internal customer data system with external CRM firms. No other API uses are allowed.

Access to such APIs is granted to partners with clear rights and licenses. Partner APIs are generally more secure and have a stronger authorization, authorization, and security features. These APIs are not usually monetized directly by enterprises; instead, partners get paid for their services and not API usage.

3. Internal APIs.

A private or internal API is one of the types of API that is only intended for use within an enterprise to connect data and systems within that organization. An internal API could connect an organization’s HR and payroll systems.

Because internal APIs are meant for internal use, security and authentication are typically weak or absent. However, this is changing as organizations become more aware of the threat and comply with regulatory requirements.

4. Composite APIs.

Composite APIs combine multiple APIs to create a series of interdependent or related operations. Composite APIs are useful for complex or closely related API behavior and can often improve performance and speed over individual APIs.

Also, read: 10 Best API Testing Tools to Use in 2023 – (SOAP and REST Tools)

Architectures and API protocols

APIs exchange commands or data. This requires clear protocols and architectures. These are the rules, structures, and constraints that regulate an API’s operation. There are currently three types of API architectures or protocols: REST (RPC), and SOAP (SOAP). These could be called “formats”, each with its characteristics and tradeoffs, and used for different purposes.

1. REST

The representational state-transfer (REST) architecture has been the most widely used approach to building APIs. REST uses a client/server model which separates the front and back ends of the API. This allows for considerable flexibility in development as well as implementation. REST is non-stateless. This means that the API does not store any status or data between requests. REST supports caching which stores responses for slow APIs. REST APIs are often called RESTful. They can also communicate with or operate through intermediate systems like API gateways, load balancers, and other APIs.

2. Remote procedural call

This protocol allows you to send multiple parameters and get results. RPC APIs execute executable actions or processes. REST APIs exchange data or resources like documents. RPC can use JSON or XML for coding. These APIs are referred to as JSON–RPC, and XML–RPC.

3. SOAP

A simple object access protocol (SOAP) is a standard for messaging that was established by the World Wide Web Consortium. It is widely used to create web APIs using XML. SOAP supports a variety of communication protocols, including HTTP, SMTP, and TCP/IP. SOAP is extensible and style-independent. This allows developers to create SOAP APIs in many ways and add functionality and features. The SOAP approach describes how the SOAP message will be processed, including the features and modules, communication protocols supported, and how to construct SOAP messages.

SOAP, unlike REST’s flexibility, is highly structured and controlled. It also has a clearly defined standard. SOAP messages can include up to four components. These include an envelope, header, and body, as well as a fault, which is used for error handling.

Comparison of API protocols

An API format’s choice can have a significant and lasting impact on its adoption and success. The complexity of the information to be exchanged and the security required around it, as well as the speed and performance that are required for those exchanges, will determine the format that is best for your organization.

A simpler format may be easier to maintain and code, but it might not provide the security and enterprise adopter needs. While more complex formats may provide greater security, they can be harder to code and maintain for users or require more work and bug fixes from developers. Although the tradeoffs are not always straightforward, there are common considerations for major API formats.

REST and SOAP are examples. Both formats are used to connect applications. They primarily use HTTP protocols and commands like Get and Post. Delete is another example. Both formats can use XML for their responses and requests. SOAP is dependent on XML, but REST can use JSON and HTML. SOAP has strict guidelines and SOAP can be modified to suit its needs. REST, on the other hand, is flexible in its rules and is controlled by architectures. SOAP is built using remote procedure calls. REST relies on resources.

Both REST and SOAP can exchange information but in different ways. SOAP is used by enterprises that require tight security and clear rules to support complex data exchanges. SOAP is often used by developers to access partner APIs or internal data. REST allows for the fast exchange of relatively simple data. REST supports greater scale, allowing for large user bases. These features make REST a popular choice for public APIs such as mobile apps.

Selecting the right type of API

Developers should be aware of the following important points, whether they are selecting an API to use in a project or creating a new API.

Clear, complete documentation – APIs require detailed documentation. Developers need to be able to refer to the usage, how-to guides, and examples of use cases for developers and users to successfully apply the API.
Ease of adoption – Make the API easy to use, such as downloading and signing up for an account. Provide solid support for developers with API knowledge that will answer any questions. Developers will abandon the API if it is too difficult or unwieldy to integrate.
Easy to use – Good APIs are simple to use and have intuitive call structures. If it makes inconsistent and cumbersome calls or responses, even the most powerful API can be ignored. A good API should be simple, consistent, clear, and backward compatible. This includes clear deprecation.
Reliability and stability – Good APIs should be developed in the same way as other software. Developers will quickly abandon buggy APIs that have inconsistent or unreliable performance. Third-party APIs must be robust and highly available.
Security – APIs should support clear authentication, where only authorized users are allowed to use the API. Any data that is exchanged over the API must be encrypted or protected from theft and snooping.

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Here are some examples of the types of APIs currently in use

APIs are essential for many modern software platforms. Many APIs are used every day by computer users without realizing their importance. Here are some examples of modern API use cases:

Social media APIs – Social platforms like Twitter and Facebook use APIs to manage communication between their platform and remote endpoints. This includes functions such as Twitter bots.
Login APIs and authentication APIs – Modern software environments rely heavily on APIs to provide some single sign-on. For example, an application might ask users to log in with Facebook. This eliminates the need to create an account for each site or app, but it effectively integrates authentication from multiple applications.
Widget, service APIs – Applications can be used to integrate small features and functions. The APIs that are used by search engines to access different service providers, such as the weather report, ocean tide schedule, and news feeds, generate content that appears in web searches. Google Maps, for example, uses an API to allow users to search for locations and plan routes using their web browser. APIs also permit maps to be added to countless third-party sites.
Payment and financial APIs – Banks often rely on APIs to connect remote users with their back-end systems to allow remote deposits, balance checks, and transfers, as well as electronic payments. An API is used by large financial companies like PayPal to connect users to PayPal accounts. They can also use PayPal to make payments on other shopping sites such as Amazon and eBay.
Booking and travel APIs – Searching for airline schedules and purchasing tickets use the airline’s API. Hotel availability and bookings are done using the hotel’s API. Trivago, Expedia, and others use custom APIs that allow users to search for and book a wide variety of accommodations and flights. However, the travel site still uses APIs from the backend to provide access to airline, hotel, and other provider APIs.
Supply-chain and shipping APIs – Packing and shipping items from their origin to their destination generates a lot of real-time information. APIs allow customers to view the status of their purchase and any shipping details such as the estimated delivery date and the current location.
Content delivery APIs and management APIs – These APIs allow users to choose the content they want and the service provider will deliver it to their device. The content is not downloaded or stored on any user’s devices.
Microservices – Software developers consider APIs essential elements in modern microservices-based software. They allow communication between many containers or modules that make up the application. A change can be made only to one module. However, testing and updating can be restricted to that module or microservice.

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