How can I get started with OpenAPI?

How can I get started with OpenAPI? #

OpenAPI, also known as the OpenAPI Specification (OAS), is a framework for defining your APIs in a way that is both human-readable and machine-readable. This allows developers to clearly understand what an API does, which endpoints are available, what parameters do they accept, and what formats they return, among other details. Whether you are a seasoned developer or a beginner, getting started with OpenAPI can greatly streamline your API development process.

In this article, we’ll walk you through the steps of getting started with OpenAPI, from understanding what it is and why it matters, to creating your first OpenAPI document, and using tools to generate code and documentation.

What is OpenAPI? #

Before delving into how to get started, it’s crucial to understand what OpenAPI actually is. OpenAPI is a specification for building APIs. Initially created by the company SmartBear, it is now maintained by the OpenAPI Initiative. The core idea is to provide a standard way of describing your API, which can then be used by tools and libraries to generate client and server code, API documentation, and more.

The specification is language-agnostic and can describe APIs based on REST principles. The primary output is an OpenAPI definition file (either in JSON or YAML format), which includes all the details about your API.

Why Use OpenAPI? #

Here are some compelling reasons to consider using OpenAPI:

  1. Standardization: It provides a standard way to describe APIs, making your APIs easier to understand for collaborators and third-party integrators.
  2. Automation: With an OpenAPI definition, you can automate the generation of API documentation, client SDKs, and server stubs.
  3. Consistency: Helps ensure consistent API behaviour.
  4. Tooling: A plethora of tools support OpenAPI, making it easier to test, document, and integrate your APIs.

Getting Started With OpenAPI #

The first step in getting started with OpenAPI is to install some essential tools that will help you create, edit, and validate your OpenAPI definitions. One highly recommended tool is Swagger, which offers a suite of tools for working with OpenAPI specifications.

You can get started by installing Swagger Editor, an open-source project that allows you to edit OpenAPI definitions in your browser.

Installing Swagger Editor Locally #

  1. Download the Swagger Editor from GitHub.
  2. Unzip the downloaded folder.
  3. Open a terminal or command prompt.
  4. Navigate to the unzipped folder.
  5. Run npm install to install dependencies.
  6. Run npm start to launch the editor.

Alternatively, you can use the online Swagger Editor which requires no installation.

Step 2: Familiarize Yourself With OpenAPI Specification #

Before you start writing your own OpenAPI definitions, it’s helpful to familiarize yourself with the OpenAPI Specification. The specification is a detailed document outlining how to describe all aspects of your API.

Here are some key components:

  • Info: General information about the API (title, description, version).
  • Paths: Defines the endpoints (/users, /items/{itemId}, etc.).
  • Operations: Methods like GET, POST, PUT, and DELETE for each endpoint.
  • Parameters: Path parameters, query parameters, headers, etc.
  • Responses: Status codes and response structures.
  • Schemas: Data models used in your API requests and responses.
  • Security: Authentication methods and authorization.
  • Tags: Group related endpoints for better organization.

Step 3: Create Your First OpenAPI Document #

Start by creating a basic OpenAPI document. Here’s an example in YAML format:

openapi: 3.0.0
  title: Simple API
  description: A simple API to get started with OpenAPI
  version: 1.0.0
  - url:
      summary: Get a list of users
          description: A JSON array of user names
                type: array
                  type: string
      summary: Get user by ID
        - name: userId
          in: path
          required: true
            type: string
          description: A user object
                type: object
                    type: string
                    type: string
          description: User not found

Step 4: Validate Your OpenAPI Document #

It’s crucial to validate your OpenAPI definitions to ensure they are correct. You can use tools like Swagger Editor, or the command-line tool Swagger CLI.

To validate using Swagger Editor:

  1. Open the editor.
  2. Copy and paste your OpenAPI definition into the editor.
  3. Look for any errors in the validation pane at the bottom.

Step 5: Generate Code and Documentation #

With your OpenAPI definition ready, you can now generate both server-side and client-side code, as well as comprehensive API documentation.

Generate Server-Side Code #

Several frameworks and tools can generate server stubs from OpenAPI definitions, such as:

Example (using OpenAPI Generator):

openapi-generator-cli generate -i openapi.yaml -g spring -o /path/to/server

This will generate a Spring-based server stub.

Generate Client-Side Code #

Similar to server-side code, you can generate client SDKs using tools like Swagger Codegen and OpenAPI Generator.


openapi-generator-cli generate -i openapi.yaml -g javascript -o /path/to/client

This will generate a JavaScript-based client SDK.

Generate Documentation #

Tools like Swagger UI can be used to generate and display interactive documentation for your API.


  • Include the Swagger UI library in your project.
  • Serve your OpenAPI definition to Swagger UI.

Your OpenAPI definitions will be rendered as interactive API documentation, allowing users to try out endpoints directly from the browser.

Step 6: Test Your API #

Testing is an integral part of the API development process. OpenAPI definitions can be integrated into testing frameworks like Postman or Hoppscotch.

Importing OpenAPI Definition into Postman #

  1. Open Postman.
  2. Click on “Import” in the top-left corner.
  3. Import your OpenAPI definition file.
  4. Postman will generate a collection based on your OpenAPI definition.

This allows you to test your endpoints directly from Postman.

Step 7: Iterate and Improve #

API development is an iterative process. Continue to refine your OpenAPI definitions, validate them, and regenerate code as necessary. Take advantage of community resources and forums to stay updated. The OpenAPI Initiative blog is a great place to start.

Conclusion #

Getting started with OpenAPI may seem daunting due to its comprehensive specification. However, by breaking down the process into manageable steps—installing essential tools, understanding the specification, creating and validating definitions, generating code and documentation, and testing—you can streamline your API development workflow significantly.

Following the steps and using the recommended tools will set you on the path to mastering OpenAPI and building robust, well-documented, and easily maintainable APIs.

For further readings, here are some useful resources:

Happy coding!

This website is not affiliated with the OpenAPI Initiative.