What is an API? Definition, Types, Specifications, Documentation

If you are here on this page, you might have read the abbreviation API earlier. Some might know about it, but some may find it a new term. 

Belonging to a mobile app development team or while learning the technicalities of apps being an expert or a beginner, you should understand what an API is and relevant information. 

This post will discuss API, working, integration, examples, benefits, types of API, and a lot more.

What is API Development?

Application Programming Interface development: API development is the process of building and maintaining APIs. An API is a stack of protocols, rules, and tools that facilitate varied software applications to communicate with each other. It defines the data formats and methods that assist apps in leveraging requests and exchanging information. 

API development includes designing, creating, testing, and documentation interfaces to facilitate interaction between varied software services, components, or systems.

What Are The Components Of API Development?

API development necessitates various key components and processes that perform together to build and maintain a functional and effective API. Such components include:

1. Programming Language and Framework

Developers leverage programming language and framework to create the API, and this decision relies on varied factors, such as team expertise, project needs, and the specific use case. 

2. API Design

Initially, API design is important because it demands defining the data models, endpoints, request and response formats, and complete API structure. Tools like Swagger or OpenAPI can help in the creation of API specifications. 

3. Data Model

APIs usually deal with data, and the data model defines the data structure the API will handle. It incorporates data types, their relationships, and their way of representation (e.g., JSON or XML).

4. Endpoints

Specific URIs or URLs that API showcases are endpoints that correspond to a distinctive functionality or resource. For instance, a RESTful API may have endpoints such as products, users, or orders. 

5. Authentication and Authorization

Implementation of security mechanisms is crucial to control API access. This comprises an authentication setup (e.g., API keys, OAuth, JWT) that verifies the user’s identity and authorization to determine the type of actions they can perform. 

6. HTTP Methods

APIs use HTTP methods, like POST, GET, DELETE, etc., to perform resources or actions. Such methods determine the operation type that must be executed on an endpoint. 

7. Response Handling

The API must generate the right responses in the anticipated format. Such responses must include related status codes, error messages, details, or data. 

8. Request Handling

The API needs to handle incoming HTTP requests, draw related data from the requests, and perform important operations on the server. This involves validating input, executing the requested actions, and parsing request data. 

9. Documentation

Developers who want to use API need proper documentation, including clear instructions on API usage, details about the available endpoints, response, and request examples, and details of authentication and rate limits.

10. Testing

Testing includes integration testing, performance testing, and unit testing, which is crucial to ensure the API is reliable and performs as expected. 

11. Versioning

As API is created, versioning is vital for backward compatibility maintenance. API’s different versions must coexist, enabling developers to migrate to the latest versions. 

12. Security Measures

Security practice implementation, such as rate limiting, data encryption, and IP whitelisting, safeguard the API from vulnerabilities and threats. 

13. Monitoring and Analytics

Monitoring and analytics tools are essential to track API usage, optimize performance, and address issues. 

14. Deployment

API deployment on servers or cloud platforms makes it accessible to users and other applications. 

15. Error Handling

Developing an error-handling process offers significant error responses that assist developers in troubleshooting issues. 

API development is an interactive mechanism, and continuous improvements and maintenance are usually in demand on requirement modification or when new features are appended. Effective API development can improve the software system interoperability and allow the integration of varied applications and services. 

API Function Calls 

Every API includes function calls, which are the language statements that pass the requests to software to perform specific actions and services. 

Function calls are composed of:

• Start and finish sessions.
• Amenities for a single room type.
• Retrieve or restore objects from a server.

In the API documentation, you can see the description of function calls. 

What does API stand for?

The acronym for Application Programming Interface, API is a software intermediary that permits two apps to communicate with each other. Every time you use an app, let’s say Instagram, send a message, or just check it on your mobile device, you are using an API. 

Considering APIs, the word:

• Application means any software with a different function.
• Interface refers to a contract of service between two apps, and it defines how the apps communicate with each other using responses and requests. 

Their API documentation includes information about how the developers need to structure those requests and responses. 

How do APIs Work?

Let’s consider the terms, client, and server to explain API architecture. 

The client is the app sending request, and the server is the app sending the response. 

As APIs ease how developers integrate new app components into a current architecture, they assist IT teams and businesses in collaborating. 

Business requirements usually change rapidly as digital markets shift, and here, new competitors can transform the entire industry with a new app. So, to stay competitive, businesses need to back the quick development and deployment of innovative services. 

A well-known way to help you speed up development is a cloud-native app, which depends on linking a microservices app architecture through APIs. 

The easiest way to link your infrastructure through cloud-native app development is through APIs. Besides, the APIs permit you to share your data with external users and customers. 

Public APIs showcase exceptional business value as they can ease and improve how you link your partners and monetize your data. 

Let’s take a real example to understand the working of APIs. 

# Example 

We will take a common scenario of flight booking.

• When you search online to book flights, you are served with varied options from which you can choose to suit your requirements. 
• You select a departure city, a return city, and dates for round-trip, cabin class, and other choices, like your seat, meal, or baggage requests. 

Whether you use the airline’s website or take the assistance of an online travel service that accumulates details from various airlines, you need access to that detail from the airline’s database. Alternatively, you may be using your phone to access the information. 

Whichever be the case, you need information. So, the app should interact with the airlines’ API, offering access to the airlines’ data. 

The API is an interface that runs and offers the data from the app you are using to the airline’s system using the internet. Then, it brings the airline’s response to your request and provides it back to the travel app you are using. 

Also, every step of the entire process allows the app and the airline’s system to interact, from seat choosing to payment and flight booking. 

So, APIs perform the same for every interaction between apps, devices, and data. They facilitate the data transmission between systems, building a connected experience. 

Types of API Architectures/API Protocols

1. RPC APIs

It stands for Remote Procedure Calls. The client performs a function on the server, and the server delivers the output back to the client. 

This protocol is the most simple of other API architectures. Unlike SOAP and REST, which allow data transfer, RPC APIs invoke processes. Or we can say these APIs execute scripts on a server. 

RPC APIs may use either XML or JSON in their calls. XML is more accommodating and more secure than JSON but otherwise is similar. 

However, the RPC protocol is strict; relatively, it’s an easy and simple way to execute code on remote networks. 

Considering security and capabilities, RPC APIs are limited. So, seen less often on the web. Although, people use it for internal systems for making process requests, specifically multiple at once. 

2. REST APIs

Representational State Transfer (REST) is an array of guidelines for lightweight, scalable, and easy-to-use APIs. The most flexible and popular APIs, the REST APIs, are found on the web. 

The client sends the requests as data to the server, and the server, in turn, uses this client request to initiate internal functions and delivers back the output to the client. 

REST defines a stack of functions, like PUT, GET, DELETE, etc., that clients use to access server data. Servers and clients perform data exchange using HTTP. 

The chief feature of REST API is statelessness, which means servers don’t save client data between requests. Client requests sent to the server are like URLs you type in your browser to go to a site. The server’s response is plain data with no typical graphical website page rendering. 

3. gRPC (Google Remote Procedural Call)

As its name indicates, gRPC was built at Google and publicly rolled out in 2015. It’s an open-source RPC framework with the caliber to run in most environments. 

This API protocol allows developers to define their custom functions to facilitate inter-service communication. 

gRPC uses HTTP as its transport later and offers extra facilities, like timeouts, authentication features, flow control, and more. 

In a language and platform independent mechanism, in protocol buffers, data is transferred that defines how easily data can be structured.

Protocol buffers start with defining the service; then, they define the data structures the service will use. 

4. JSON-RPC (JavaScript Object Notation- Remote Procedural Call)

It was launched in the early 2000s, and it performs extensively with JSON to offer a limited but simple implementation of API communication. 

JSON-RPC defines an array of calls that can easily manage entire functionalities defined under their scopes and reveals an enhanced performance over REST in such circumstances. 

Altogether, JSON-RPC is stateless and lightweight and uses request objects and response objects to create communication among the web services.

5. GraphQL

Stands for Graph Query Language; GraphQL was developed at Facebook and launched in 2015; GraphQL performs well while allowing API communication. Like database query languages, such as SQL, GraphQL queries data from the server. We need to define the data we want and its format in the query, and in turn, GraphQL returns the data in the exact format you requested. 

This leads to time and memory saving as just the required data is queried from the server, despite importing the whole package files with various other details. 

GraphQL is developed to back a variety of web development languages. 

6. Apache Thrift

Developed at Facebook; Apache Thrift was created differently than GraphQL. This API protocol is an implementation of the RPC framework that uses code for defining the client and server sides. This is met using Thrift files. 

The code syntax is intuitive and flexible. Ahead of this, the code generation engine produces the needed code in any programming language that the developer specifies. 

Thrift is built targeting two chief goals: 

• Allowing communication with services written in varied languages and scalability. 
• The code generation usage makes the services flexible. 

For real transportation of data, Thrift holds runtime libraries that allow inter-service communication. Thrift architecture defines such libraries at a varied level from the service for which the developer writes the code. So, in Thrift, the changes can be done easily with no need to recompile modified code from scratch, as most basic elements stay unaffected by the changes. Thrift supports HTTP transmission and from binary transport formats. 

7. XML-RPC(Extensible Markup Language Remote Procedural Call)

This API protocol is quite similar to JSON RPC, except the data is encoded and shared as XML files through HTTP/HTTPS for transmission. XML utilizes in-built vocabulary to describe the nature of requests and responses. The client reads out the procedure to be called, and the supporting parameters are next transmitted using HTTP in the request. The receiver sends an XML response that can be the data called, or a fault is returned. 

XML-RPC is restricted by its dependency on XML as the complex objects can’t be encoded properly in XML, which can’t include data not defined in its vocabulary. 

8. SOAP APIs

This protocol transmits data across networks and is used to develop APIs. This API is standardized by the World Wide Web Consortium (W3C) and uses XML to encode information. Well, this less flexible API was widely known a few years back. 

SOAP defines message inclusion and way of delivery, which makes this API more secure than REST APIs. However, the rigid guidelines make this API harder to implement and more code-heavy. 

That’s why SOAP is usually implemented for internal data transfers that need high security. The users can deploy more flexible REST architecture everywhere else. 

9. Websocket APIs

One more modern web API development, Websocket API, uses JSON objects to pass data. This API backs two-way communication between the client apps and the server. This API facilitates the server to deliver callback messages to the connected clients, making it more efficient than REST API. 

API Release Policies – Types of API

Regarding release policies, API can be Private, Partner, Public, and Composite. 

1. Private

The API is for internal use only. So, the companies hold the most control over their APIs and use them to make data exchange between teams and systems flawless.

Also known as Internal APIs, Private APIs are not for third-party usage. 

These APIs are hidden from the public as private APIs are not documented in a publically released SDK. Though, various brands go public with their internal APIs. 

One can use these APIs for internal data transfer that can be more secure, efficient, and traceable. Also, it’s a scalable solution when a business emerges with a new internal system; this system holds the caliber to interact with current systems via their APIs. 

2. Partner

The API is shared with particular business partners, which can offer extra revenue streams without compromising the quality.

These APIs are shared among those who hold a business link with the company offering the API. 

Access is restricted to authorized clients holding official licenses, and with partner APIs, security measures are stronger than open APIs. 

Some businesses prefer Partner APIs because they demand strong control over who can access their resources. 

3. Public

Everyone has an API that facilitates third parties to build apps that communicate with your APIs and may lead to innovation. 

Also known as Open APIs, Public APIs are available to every developer. Resultantly, Public APIs hold comparatively low authorization and authentication measures and are usually confined to the assets they share. 

Some open APIs are free, while others need a subscription fee, often arranged according to the number of calls made to APIs. 

Making APIs public can be beneficial for sharing data publicly. This motivates any external developer or business to integrate with the app to which API belongs, making the API and the third-party software more valuable. 

Open API permits easy implementation, and with no restriction, 3rd-parties can rapidly use the data it offers.

4. Composite 

Composite APIs integrate various APIs permitting developers to stack calls or requests and receive a single response from different servers. You may use a composite API if you want data from multiple apps or sources. Or you can use this API to set an automatic bundle of calls and responses without your interference. 

As composite APIs diminish the number of total API calls, it may lead to faster systems, less server load, and reduced system complexity.  These APIs are commonly deployed in microservices where one task may demand data from multiple internal APIs to get it done. 

APIs by Use Cases

APIs are also classified according to the systems for which they are crafted. 

a. Operating Systems APIs

This APIs group defines how the app uses the OS services and resources. Every OS arrives with its stack of APIs, for example, Linux API or Windows API. 

Apple offers API references for iOS and macOS in its developer documentation. APIs for developing apps for the macOS desktop operating system are carried in the Cocoa set of developer tools. 

Those developing apps for the iOS mobile OS use Cocoa Touch, Cocoa’s modified version. 

b. Web APIs,

The most common API class is Web APIs. These offer machine-readable data and the functionality transfer between the web-based systems that showcase client-server architecture. Such APIs deliver requests from web apps and responses from servers using HTTP. 

Developers can consider web APIs to extend their apps’ or websites’ functionality. 

Many businesses use various APIs to connect apps and share information. Some demand an API management tool to assist them in distributing, analyzing, and controlling different APIs. 

c. Remote APIs

These APIs define apps’ integration standards for running on varied machines. Or we can say one software product accesses resources outside the device that requests them.

As two remotely placed apps are linked over a communications network, specifically the internet, various remote APIs are written according to web standards. 

Examples – Java Remote Method Invocation API and Java Database Connectivity API. 

What are API Integrations?

API integration is known to connect two or more apps via their APIs (application programming interfaces) that permit data source exchange between systems.

In other words, API integration is system-to-system via APIs, permitting those systems to exchange data. APIs are crafted to facilitate the use of a system remotely and connect systems, IoT devices, people, and more. 

Moreover, it strengthens the processes throughout various sectors and layers of a company to sync data, improve productivity, and boost revenue. 

Two or more systems with APIs can interact in real-time using those that save money and time and are more reliable considering data accuracy and information currency. 

Earlier, we might have emailed or faxed this information or shared it on the phone. But, with API integration, everything takes place digitally, without human interference. 

How to Achieve API Integration?

Well, it relies on a specific system or business needs. 

1. Custom Integrations

It includes a hand-crafted script from a software developer holding profound knowledge and understanding of the API documentation. This technique was famous a few years back, but the development cost and constant maintenance have made it less preferred before new integration modes. It’s also time-consuming to complete this approach. 

2. Connector Applications

These are crafted to ease the data transfer between two popular software platforms. Connectors are reasonable, let standard API deployment solutions quicker, and ease integrations to manage and maintain. Also, they diminish the API management need. 

API Integration Process

You can choose from various API integration tools, and after you choose your preferred one, you should follow a specific process that features three important parts. 

• Evaluate your business processes and goals.
• After identifying business pain points, figure out how internal and external platform integration can assist in reducing these issues. 
• Get support from individuals like System Admins and Software Analysts, who can make your integration efforts win and highlight your enterprise’s benefits. 
• Now, you can start the development and build a custom app. 
• Then, you can interact with APIs of the software platforms to craft new functionalities that assist in attaining your goals. 
• At last, you should perform some tests on your system to ensure that the integration app is bug-free and meets your business needs. 

What are the Benefits of API Integration?

Several notable benefits one can reap from API integration.

1. Scalability

API integration facilitates businesses to grow as there’s no need to start from scratch when crafting connected apps and systems. 

2. Automation

You can automatically deliver data and information from one app to another via API integration. This automation assists remove the manual component that reduces errors and saves time.

3. Innovation

The development of a new app can alter the entire industry. So, businesses need to revert rapidly and support the quick deployment of the latest services. So, to attain all these requirements, businesses can make changes at the API level without re-writing the entire code. 

4. Expansion

APIs offer an exceptional opportunity for businesses to fulfill clients’ requirements across various platforms. 

For example, maps API facilitates the integration of map information via sites, iOS, Android, etc. Businesses can use free or paid APIs to provide similar access to their internal databases.

5. Diminishes Errors

API integration permits the transfer of voluminous and complex data with reduced inadequacies and errors. 

6. Streamlined Communication/Visibility/Reporting

API integration permits end-to-end visibility of all processes and systems for enhanced reporting and communication. With a smooth approach, you can effectively track and monitor data. Thereby crafting robust reports based on complete and specific datasets. 

7. Ease of Maintenance

The API performs like a gateway between two systems. Every system is required to make internal modifications that may not affect API. This way, if one party makes changes. It doesn’t impact the other parties. 

How to use an API?

You can implement a new API following the below steps:

• Obtain an API key: You can perform this by crafting a verified account with the API provider. 
• Setup an HTTP API client: This tool lets you easily structure API requests using the received API keys.
• In the absence of an API client, you can structure the request in your browser by referring to the API documentation.
• After being comfortable with your new API syntax, you can start including it in your code. 

What is an API Endpoint, and Why is It Important?

The final touchpoints in the API communication system are API endpoints that include services, server URLs, and other particular digital locations from where details are delivered and received between systems. API endpoints are important for enterprises for two primary reasons:

a. Performance

API endpoints, specifically high traffic ones, can hinder system performance and cause bottlenecks.

b. Security

Systems become vulnerable to attack because of API endpoints. That’s why API monitoring is important for avoiding misuse.

API Examples

Obviously, it’s not easy to understand APIs with no information about their real-life apps. 

1. Pay with PayPal

PayPal is a fintech service that permits users to link personal information to their PayPal accounts. This leads to easier and more secure money transfers. 

PayPal embeds into any number of sites that need financial transactions.

The sites interacting with PayPal wouldn’t have direct access to your card or band info. API integration offers security in this.

2. Travel Booking

It’s a useful API because most travel websites target making links and building relationships. 

Travel websites, like Expedia and Trivago hold the strength to feature and sell various all-inclusive travel packages that provide lodging and travel. 

3. Google Maps

Google Maps API offers users the benefits of various geographic aptitudes. You can search nearby niche shops, restaurants, and anything. 

The active Google Maps API is used whenever you see business hours, contact information, reviews, or whatever on your screen. 

4. Ecommerce 

It includes the act of performing commercial activities, such as buying and selling goods online. PayPal is a service typical for eCommerce. 

Generally, APIs are a huge part of eCommerce, offering eCommerce platforms speed, security, and scalability. eCommerce platforms’ functions, such as currency conversion and site search, need APIs to operate properly. 

These are just a few examples of APIs; you can catch up with more by digging deep into a pool of APIs. 

What is API testing? Where is it Performed?

In software app development, API is the middle layer that exists between the database later and the presentation (UI) layer. APIs allow communication and data exchange between software systems. 

API testing is a software testing practice that is best for direct API testing from reliability, performance, and functionality to security. API testing, a part of integration testing, helps validate the logic effectively to craft architecture within a short span. 

Three separate layers exist in a typical app, the database, the business, and the presentation (or UI) layer for data modeling and manipulation.

API testing is performed at the business layer, the most critical layer in which business logic processing is conducted, and entire transactions between the database and user interface layers take place. 

Also read: Emulator vs Simulator for Mobile Testing & Debugging

What is an API gateway?

An API Gateway uses a wide range of back-end services as an API management tool for enterprise clients. These gateways typically manage common tasks, such as statistics, user authentication, and rate management, that you can apply across every API call.

How to Write API Documentation?

In the API management process, we need to write complete API documentation. API documentation can be written manually or auto-generated using the tools. 

API documentation includes some best practices that should be performed:

• Use easy-to-read and simple English to write explanations. Documentation generated using tools can become wordy and may demand editing.
• Explain functionality using code samples.
• Documentation needs to be maintained to make it accurate and updated.
• Cover entire issues that API can resolve for the users. 

How to Create an API?

An API development needs effort and diligence that other developers can trust and would like to work with. 

The APIs development process is simple. Let’s check how to develop APIs. 

a. Determine Your API Requirements. 

Start with determining API needs that can be a combination of  functional and non-functional requirements.

Functional requirements will include the tasks you want your API to perform. Simply put, what business caliber does an API shows to its consumers?

Non-functional requirements will be a blend of service level concerns. This includes the expected API response time and performance, among others. Also, it covers downstream systems’ integrity and data protection.

Consider the below questions to accumulate the API requirements:

• Who is your audience – external developers, internal developers, or both?
• How can you include these requirements into the API?
• What are your expectations concerning API availability, response time, and performance?
• What concerns do you need to target from an API security perspective? 

After accomplishing this step, you can move on to the next step.

b. Design an API

Now, it’s time to design an API. How to design it. Are there any internal rulebooks that can guide your API design? Will you first choose to design your API interface and, after that, craft the backend resources to link it? Or do you need to publish a current resource as an API product?

c. Develop Your API

Next; it’s time to start with API development. 

While developing your API, you need to cover the below essentials:

• Craft a meaningful name for your API with a useful description.
• Define operations your API will perform.
• Define the data model that describes perfectly the request and response messages.

You can use a tool to develop your API easily. In this, you can choose any of the two ways:

• You can create an API from scratch and, next, connect it to current resources. 
• You can develop your API that uncovers an existing resource. 

Besides, you can use a current resource as a fundamental to develop your API product. 

Whatever approach you pick, in the end, your API will demand a connection to its downstream resource. In the beginning, it will address these resources in a test environment. 

d. Test Your API

After you build your API, it’s time for API testing. 

Obviously, to conduct testing, you need a testing environment. But, while developing an API, you need to consider some testing specifications. 

The chief objective of testing API is to ensure your API performs as expected under multiple conditions. Also, you should test the security of your API and validate any other important non-functional requirements. 

To test your API properly, your API needs to be linked to a resource that mocks the final product resource. 

On the other hand, you can configure your API to return a mock response; which is an easy way in the absence of downstream resources. 

One of the mostly-preferred ways to test API is to pair your API platform with a test automation platform, like Perfecto. Some platforms, like Akana, offer an integrated test client that facilitates both functional testing and validating if security policies are fulfilled. Besides, Perfecto offers an automation platform that paces up test execution. 

e. Deploy Your API

After testing and reviewing your API; you need to deploy it in production. 

Enterprise APIs are generally hosted on API gateways, like cloud APIs that make sure the expected security, scalability, and performance needs are met. 

You should publish APIs in an API developer portal to ease their adoption. You can improve API adoption by providing clear documentation that outlines API functions and applicable use cases. Additionally, it needs to explain applicable API security constraints clearly. 

Developers can properly understand the API and its related features (functional and from a security perspective) using an interactive tool. 

Preferably, the testing tools showcase the API in a sandbox environment, which permits testing without using real production data or linking to production systems.

Moreover, you can monetize your APIs by offering your API in subscription plans with tiered pricing.

f. Monitor Your API

After you finish testing and deploying your API, you need to monitor it to understand its usage and performance. 

You can consider the below metrics to monitor your API:

• API metrics, such as consumption and engagement.
• Operational metrics, such as throughput and availability. 
• Business metrics, such as how API performs and affects a business. 

Various APIs are for monitoring, but selecting a platform with in-built analysis will ease API monitoring.

Where to find New APIs?

You can get new web APIs from API directories and API marketplaces. 

• API Directories: These are controlled repositories controlled by the directory owner. 
• API marketplaces: These are open platforms where anyone is permitted to list an API for sale. 

Adroit API designers are allowed to access and test a new API and, after that, add it to their directory. 

How can we help you in building an API or Integrating API to a website or app?

Well, it’s not easy for every brand to build and integrate APIs as it demands various technicalities and expertise to let the workflow move flawlessly after the API integration. 

If you are also devising to develop and  integrate APIs into your business app, you can achieve that by connecting with the best mobile app development company. We will help you in meeting your objectives efficiently and with no hassle. 

Wrapping Up

The APIs play a vital role not only in software and app development but also in business collaboration. Such machine-readable interfaces for the resource exchange are like delivery services and enable the required technological connectivity. 

So, the decision-makers and developers need to pick the API that performs for a company’s particular business requirements and understand how to use them effectively. 

We hope this post proved to be helpful for you in understanding APIs and relevant information about them.