Last Updated: 09 Oct, 2020

What Is API: Definition, Types, Specifications, & Documentation

Reading time:

Have you ever heard the word “API” batted about, and wondered exactly what this is? Do you have a vague idea, but want to know more about what you might do with an API, and how you might build one? Don’t fret. We can help!

Let’s get down to it and pick apart what an API is, and how building an API is similar (or different!) than building other types of web apps and websites. Here’s a short primer on what an API is, what makes it different, and what you would need to build one yourself.

What Is An API? (Application Programming Interface)




API is the acronym for Application Programming Interface, which is a software intermediary that allows two applications to talk to each other. Each time you use an app like Facebook, send an instant message, or check the weather on your phone, you’re using an API.

Travelopro is a Travel portal development company providing Online Travel Portal Solutions & Booking Engines to Travel agents. If you are developing your travel business, we are here to help you find all the travel portal development related solutions. 

Travelopro is specialized in portal design, development, and integration of various GDS’s XML, API’s, testing & deployment to client domain after which we also maintain the technical and customer support services. Travelopro helps those who are looking for online travel portal development services and B2B & B2C Online Travel Portals.

We provide travel portal software services for B2C and B2B models and travel portal API integration for online hotel booking system, car bookings, flight booking system, holiday booking system, tour reservation system, bus bookings, payment gateway integration, insurance, and cruise booking etc. 

As per the requirements, Travelopro integrates the client's travel portal with tools such as weather widget, Google maps and various information sources providing the latest travel news, trip advice and travel guides which will help travelers in planning their trip accurately while making the travel portal more attractive and informative to customers.

Travelopro, APIs let your product or service communicate with other products and services without having to know how they’re implemented. This can simplify app development, saving time, and money. When you’re designing new tools and products or managing existing one’s APIs give you flexibility; simplify design, administration, and use; and provide opportunities for innovation.

APIs are sometimes thought of as contracts, with documentation that represents an agreement between parties: If party 1 sends a remote request structured a particular way, this is how party 2’s software will respond.

Because APIs simplify how developers integrate new application components into an existing architecture, they help business and IT teams collaborate. Business needs often change quickly in response to ever-shifting digital markets, where new competitors can change a whole industry with a new app. 

In order to stay competitive, it's important to support the rapid development and deployment of innovative services. Cloud-native application development is an identifiable way to increase development speed, and it relies on connecting a microservices application architecture through APIs.

Travelopro APIs are a simplified way to connect your own infrastructure through cloud-native app development, but they also allow you to share your data with customers and other external users. Public APIs represent unique business value because they can simplify and expand how you connect with your partners, as well as potentially monetize your data (the Google Maps API is a popular example).

What Is An Example of An API?

For example, imagine a book-distributing company. The book distributor could give its customers a cloud app that lets bookstore clerks check book availability with the distributor. This app could be expensive to develop, limited by platform, and require long development times and ongoing maintenance.

Alternatively, the book distributor could provide an API to check stock availability. There are several benefits to this approach:

  • Letting customers access data via an API helps them aggregate information about their inventory in a single place.
  • The book distributor can make changes to its internal systems without impacting customers, so long as the behavior of the API doesn’t change.
  • With a publicly available API, developers working for the book distributor, booksellers, or third parties could develop an app to help customers find the books they’re looking for. This could result in higher sales or other business opportunities.

In short, APIs let you open up access to your resources while maintaining security and control. How you open access and to who is up to you. API security is all about good API management, which includes the use of an API gateway. Connecting to APIs, and creating applications that consume the data or functionality exposed by APIs, can be done with a distributed integration platform that connects everything including legacy systems, and the Internet of Things (IoT).

When you use an application on your mobile phone, the application connects to the Internet and sends data to a server. The server then retrieves that data, interprets it, performs the necessary actions and sends it back to your phone. The application then interprets that data and presents you with the information you wanted in a readable way. This is what an API is - all of this happens via API.

Innovating with APIs

Exposing your APIs to partners or the public can:

  • Create new revenue channels or extend existing ones.
  • Expand the reach of your brand.
  • Facilitate open innovation or improved efficiency through external development and collaboration.
  • Sounds great, right? But how can APIs do all that?

Let’s return to the example of the book distributing company.

Suppose one of the company's partners develops an app that helps people find books on bookstore shelves. This improved experience brings more shoppers to the bookstore—the distributor's customer—and extends an existing revenue channel.

Maybe a third party uses a public API to develop an app that lets people buy books directly from the distributor, instead of from a store. This opens a new revenue channel for the book distributor.

Sharing APIs?with select partners or the whole world?can have positive effects. Each partnership extends your brand recognition beyond your company’s marketing efforts. Opening technology to everyone, as with a public API, encourages developers to build an ecosystem of apps around your API. More people using your technology means more people are likely to do business with you.

Making technology public can lead to novel and unexpected outcomes. These outcomes sometimes disrupt entire industries. For our book distributing company, new firms, a book borrowing service, for example, could fundamentally change the way they do business. Partner and public APIs help you use the creative efforts of a community larger than your team of internal developers. New ideas can come from anywhere, and companies need to be aware of changes in their market and ready to act on them. APIs can help.

Types of APIs




Discussing different types of APIs, alongside protocols and standards, such as Open APIs, Internal APIs, Partner APIs, Composite APIs, RESTFUL, JSON-RPC, XML-RPC, and SOAP.

APIs (Application Programming Interfaces) come in many forms. API designers can choose from a range of protocols and standards when creating a new API, depending on the type of API they are creating, and its purpose. This article takes a look at a few important API types and protocols, including REST API protocols.

Web APIs

Web APIs are APIs that can be accessed using the HTTP protocol. The API defines endpoints, and valid request and response formats. Web APIs include the APIs used to communicate with the browser (see list). There may be services such as web notifications and web storage. Different web APIs feature varying levels of security and privacy, including open, internal, and partner APIs. Multiple web APIs can be combined into a composite API - a collection of data or service APIs.

Open APIs

Open APIs, also known as external or public APIs, are available to developers and other users with minimal restrictions. They may require registration, and use of an API key, or maybe completely open. They are intended for external users (developers at other companies, for example) to access data or services. As an example, take a look at the provided by the UK government. Any developer can access it, without even registering, allowing app builders to include governmental data on restaurant standards in their apps.

Internal APIs

In contrast, to open APIs, internal APIs are designed to be hidden from external users. They are used within a company to share resources. They allow different teams or sections of a business to consume each other’s tools, data, and programs. Using internal APIs has several advantages over conventional integration techniques, including security and access control, an audit trail of system access, and a standard interface for connecting multiple services.

Partner APIs

Partner APIs are technically similar to open APIs, but they feature restricted access, often controlled through a third-party API gateway. They are usually intended for a specific purpose, such as providing access to a paid-for service. This is a very common pattern in software as a service ecosystem.

Composite APIs

Composite APIs allow developers to access several endpoints in one call. These could be different endpoints of a single API, or they could be multiple services or data sources. Composite APIs are especially useful in microservice architectures, where a user may need information from several services to perform a single task. Using composite APIs can reduce server load and improve application performance, as one call can return all the data a user need.

API Architectures and Protocols/Specifications




An API protocol defines the rules for API calls: it specifies accepted data types and commands. Different API architectures specify different protocol constraints.

The goal of API specifications is to standardize data exchange between web services. In this case, standardization means the ability of diverse systems, written in different programming languages and/or running on different OSs, or using different technologies, to seamlessly communicate with each other.


REST (representational state transfer) is a very popular web API architecture. To be a REST API, an API must adhere to certain architectural constraints, or principles, including:

Client-server architecture: the interface is separated from the backend and data storage. This allows for flexibility, and for different components to evolve independently of each other.

  • Statelessness: no client context is stored on the server between requests.
  • Cacheability: clients can cache responses, so a REST API response must explicitly state whether it can be cached or not.
  • Layered system: the API will work whether it is communicating directly with a server, or through an intermediary such as a load balancer.


An RPC is a remote procedure call protocol. XML-RPC uses XML to encode its calls, while JSON-RPC uses JSON for the encoding. Both protocols are simple. A call can contain multiple parameters, and expects one result. They have a couple of key features, which require a different architecture to REST:

  • They are designed to call methods, whereas REST protocols involve the transfer of documents (resource representations). Or, to put it another way, REST works with resources, whereas RPC is about actions.
  • The URI identifies the server, but contains no information in its parameters, whereas in REST the URI contains details such as query parameters.


SOAP (simple object access protocol) is an established web API protocol. It is intended to be extensible, neutral (able to operate over a range of communication protocols, including HTTP, SMTP, TCP, and more), and independent (it allows for any programming style) The SOAP specification includes:

  • The processing model: How to process a SOAP message.
  • Extensibility model: SOAP features and modules.
  • Protocol binding rules: How to use SOAP with an underlying protocol, such as HTTP.
  • Message construct: How to structure a SOAP message.

API Documentation




There are many opportunities for creating and extending software products which are provided by API’s; there would be an unusable part of code if the developers didn’t understand how to work with it.

There is well-written and structured API documentation which explains how you can effectively use and integrate an API in an easy to comprehend manner and will make a developer happy and eager to recommend the API to others.

There are numerous contents that can help in making good documentation they are:

  • A quick start guides for what is API
  • API authentication information
  • API call requests explanation
  • API examples with every request and return response description, or error messages, etc.
  • Sample of code for popular programmatic languages like JAVA, Python, JavaScript, or PHP.
  • API tutorials
  • SDK examples which illustrate how to access the resources and much more.

It could be possible that documentation could be static or it could be interactive. The documentation allows trying out API's and see return results and they usually consist of two columns which are humans and machines. The first human column contains API descriptions and on the other hand, the machine column has a console to make calls and also contains information that the clients and servers will be more interested in when they test API.

Generating API documentation is generally done by developers and technical writers. The documentation specialist must use API documentation solutions to make a unique structure and design. One can take help from tools like Postman, Slate, Re-Doc, and Swagger to make unified documentation.

The Business Benefits Of Using APIs

  • Integration with third-party apps, which provide real-time functionality or manage computations, without needing to write your own complex algorithms (this is true for e-commerce, finance and other industries).
  • Empower your lead generation or CRM apps with social insights (by matching email addresses against social media profiles).
  • Integration web/mobile apps with cloud storage of files.
  • Integration mobile apps with a remote backend to push files and retrieve data.

Why Choose Travelopro API Development Company




Travelopro gives you modular, lightweight, and comprehensive API solutions that are open source, open standards, and available on-premise or in the cloud. They're a big part of how you can change your existing integration infrastructure to be more flexible and deliver value more rapidly.


Travelopro API specialists, who have extensive experience in providing API development and integration services, using C, C++, Java, Python, and PHP, create powerful, secure, and easily maintainable APIs. Our API masters have technical expertise in working with the most popular APIs such as Google APIs, Yahoo APIs, Social Media APIs (Twitter, Facebook, LinkedIn, Instagram), Marketplaces APIs (eBay), other APIs, and mashups.

API Costs: 

Hire our dedicated API developers and get significant cost-savings. Why? First, the total cost of your project will be much cheaper than the cost of the same project development in Western Europe or the USA. Secondly, our skilled and experienced developers leverage the latest technologies and follow best practices, so our APIs are built secure and high-performance that let’s avoid wasting time and money on support and maintenance.


We successfully build APIs of high performance and security for any industry and right for your specific requirements. Our developers use the SOAP / REST API methods to provide data processing in different programming languages. We document all the APIs using Swagger to make them more convenient to work with


We are experts in creating new APIs and integrating your application with an interface of an existing API. Our team of experienced IT specialists offers API development and integration services, providing you with custom rich in functions API solution.

Custom API development

We apply individual approaches while strictly following the REST architecture. We provide a clean and well-structured programming code, use the best development tools, and build high-performance APIs for your needs.

Mobile API development

We create APIs, which let you make payments, appointments, find a geolocation etc., to enrich your mobile applications.

API development for Cloud computing: 

Cloud-based APIs allow integrating different applications into the Cloud. They can be cross-platform or specific. We develop cloud-based APIs for social networking, keeping/sharing documents, photos, video, and other data in the cloud, etc.

Web API development

Web API is a set of Hypertext Transfer Protocol (HTTP) request messages. Building Web APIs, we use the latest representational state transfer (REST) and resource-oriented architecture (ROA) styles. We also create mashups and web APIs for social media.

API Integration: 

API integration means setting smooth communication between diverse software components, technologies, and programs: integration with Google, Yahoo!, PayPal, Amazon, Skype, Facebook and Twitter; integration with JS, XML, RESTful APIs; integration with Oracle web services and much more.

API consulting: 

We will analyze your current processes and architecture, help you develop a strategy and a plan, identify and eliminate issues before they become real problems. With extensive experience, we will also help you make the right choice of API management and API integration solutions that will meet all your needs. Our recommendations are developed based on rigorous analysis, taking into account code, processes, security, and architecture.

If you have any questions on the API and the payment solution flexibility we can offer with your CRM, accounting or website software feel free to contact us at Travelopro.



If we take a look at API's then the role of API is definitely greater if we see from it the software development side or from the business perspective angle. There has been a vast study made which states that more than 60% of the businesses are partnering through these API.

There are two main tasks for the developers and the decision-makers and that is to select the specific API that works for the company-specific business needs and the second one is how to effectively use it.


Sort by : newest | oldest | most voted
Samual Jane
Oct 10, 2020

Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum is simply dummy solution

Aby John
Sep 20, 2020

Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum is simply dummy solution


Click on the Tomato to prove you're human.