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What Is Open API? Pros, Cons, and Examples

Girl using open api

In recent years, Open API has become a buzzword in the tech industry, and for good reason. Answering the question ‘What is Open API?’, Open API, also known as RESTful API, is a type of application programming interface that enables developers to access and interact with the functionalities of an application or service over the Internet.

With its emphasis on interoperability and standardized communication protocols, Open API has rapidly gained popularity among software developers and businesses alike. In this blog post, we’ll take a closer look at Open API, its pros and cons, and provide some real-world examples of how it’s used in various industries.

Whether you’re a seasoned developer or just starting out, this article will help you understand what Open API is all about and how you can leverage it in your projects.

Developer using open APIs & using common programming naming conventions

What Is Open API?

An Open API (Application Programming Interface) is a publicly accessible software interface that allows developers to access and interact with a specific application or service.

It uses well-defined, machine-readable request and response formats, such as JSON or XML. This is how it helps us to enable seamless communication and integration between different software systems.

Note that an Open API is not a private API. Moreover, it can help us connect to software without accessing its source code.

What Is the History of Open API?

Open API, also known as Swagger, is a specification for building and documenting RESTful APIs. It was created by Tony Tam and his team at Reverb Technologies in 2010, with the goal of simplifying API development and consumption. In 2015, Reverb was acquired by SmartBear Software, which now manages the Open API initiative.

Since its inception, Open API has undergone several iterations, with version 3.0 being the latest and most widely used. The standard has been embraced by developers worldwide and is supported by a growing number of code-generation tools and frameworks.

Its popularity can be attributed to its ability to streamline API development and enable seamless communication between disparate systems. Moreover, Open API has also been instrumental in promoting API-driven development and the use of microservices architectures.

Why Is Open API a Popular Standard?

Open API is a popular standard for building and documenting RESTful APIs because it simplifies API development and consumption.

Moreover, it enables seamless communication between disparate systems and promotes API-driven development and the use of microservices architectures. Additionally, its widespread adoption has led to a thriving ecosystem of tools and frameworks.

What Is the Format of an Open API?

The format of an Open API document is written in YAML or JSON. Here’s an example of a simple Open API document in YAML format with default value:

What Data Types Open API Support?

Open API supports a variety of data types, including primitive types such as strings, numbers, and booleans, as well as more complex types such as arrays and objects. Furthermore, it also supports common data formats like JSON, XML, and binary. Additionally, Open API allows for the definition of custom data types using JSON Schema.

girl checking twitter feed to run an API call

What Is the Structure of an Open API?

From the above discussion, we have learned about the following three facts:

  1. Open API is a YAML or JSON object.
  2. It supports complex data structures and common data formats.
  3. Open API is standard for documenting and building REST APIs.

Now, let’s discuss the structure of an Open API. Here is the structure of an Open API.

You must know that every section has key-value pairs or priorities. These all provide you with the API specifications or metadata.

What Does an Open API Documentation Contain?

An OpenAPI document contains the following important sections:

External Docs – Contains links to additional API documentation.

Tags – Provides metadata, allowing for the specification of the order in which each API resource displays.

Components – Contains reusable schemas for request bodies, response schemas, and security schemes.

Paths – Contains the relative paths to the separate endpoints of the API.

Security – Declares the type of security scheme authorizing requests.

Servers – Contains the connection details to a server object or multiple server objects.

Info – Contains metadata that can be leveraged by tooling.

OpenAPI – Specifies the version of the OpenAPI specification.

What Are the Open API Strengths?

Here are the strengths of Open API(public API):

Clear Documentation

OpenAPI’s specification provides a clear and structured way to document RESTful APIs. It helps in creating interactive and user-friendly documentation. Moreover, it is compatible with different programming languages.


OpenAPI provides a standardized way to define and document APIs, ensuring consistency across different API versions, teams, and organizations.

This promotes good API governance practices, reducing errors and improving the overall quality of the API.


OpenAPI is a language-agnostic specification that can be used with any programming language or framework. This allows for a greater level of flexibility and interoperability between different systems.

Wide Adoption

OpenAPI has been widely adopted and is supported by a large community of developers, making it easier to find support, resources, and tools.

Robust Tools

OpenAPI has a rich ecosystem of tools and frameworks that support the entire API lifecycle, including design, development, testing, and deployment.

Girl describing rest apis

What Are the Open API Weaknesses?

Here are OpenAPI weaknesses:

Less Useful for API Design and Planning

While OpenAPI is excellent for documenting an existing API, it may not be as helpful for designing and planning an API from scratch.

Not Hierarchical

OpenAPI doesn’t support hierarchical structures, which can make it difficult to represent complex relationships between API resources.

Does Not Support Data Model Inheritance

OpenAPI does not support data model inheritance, which can be problematic when dealing with complex data models.

Not a “Visual” Tool

OpenAPI is a text-based specification, which can make it difficult for some users who prefer visual tools to design and document their APIs.

Lack of Support for Other Architectures

OpenAPI is focused on RESTful APIs and may not be as suitable for other types of APIs, such as SOAP-based APIs or event-driven architectures.

What Are Open API Examples?

OpenAPI examples refer to sample specifications that showcase how to document an API using the OpenAPI specification.

Petstore API

A basic example that demonstrates how to document a simple RESTful API for managing pets and their associated categories and tags.

Swagger UI

An interactive documentation tool that allows users to explore and interact with an OpenAPI specification.

OpenAPI tutorial

A step-by-step tutorial that walks users through the process of creating an OpenAPI specification for a hypothetical “Todo” API.

Microsoft Graph API

A comprehensive example that documents Microsoft’s Graph API using the OpenAPI specification, including details on authentication, error handling, and available endpoints.

These examples demonstrate the flexibility and versatility of the OpenAPI specification, as well as its ability to document a wide variety of APIs.

man working with closed API or private APIs

Final Thoughts

OpenAPI is a powerful tool for documenting RESTful APIs. It provides a standardized way to describe the various endpoints, parameters, and responses of an API, making it easier for developers to understand and use the API.

OpenAPI has many benefits, including clear documentation, language-agnosticism, and wide adoption, which have contributed to its popularity in the developer community. However, it also has some limitations, such as its limited support for other architectures and lack of support for data model inheritance.

Despite these weaknesses, OpenAPI remains an essential tool for API documentation and has numerous examples that demonstrate its flexibility and versatility. Ultimately, it is up to developers to determine whether OpenAPI is the best solution for their project’s needs.


What Is Meant by Open API?

Open API (sometimes written as OpenAPI) is a specification for describing RESTful APIs, also known as web APIs, in a standardized format.

What Is Open API vs Rest API?

OpenAPI provides a way to document a RESTful API, while REST defines how the API should function.

What Can Open API Do?

OpenAPI can document RESTful APIs, facilitate communication between different software systems, and generate client libraries and server stubs.

Does an OpenAPI Mean It Is Free?

No, OpenAPI is a specification for documenting APIs, it is not a product or service and does not have a cost.

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