How to Convert Postman Collections to OpenAPI 3.0: A Step-by-Step Guide

As a developer working with APIs, you're likely no stranger to Postman, a popular tool for testing and documenting your endpoints. However, when it comes to sharing your API documentation in a standardized format like OpenAPI 3.0, you might find yourself at a loss.

Fear not! This comprehensive guide will walk you through the process of converting your Postman collections to OpenAPI 3.0 specifications, with a focus on the popular postman-to-openapi npm package.

Why Convert Postman to OpenAPI?

Before getting strated, let's quickly touch on why you might want to convert your Postman collections to OpenAPI:

• Standardization: OpenAPI is an industry-standard for describing RESTful APIs, ensuring that your documentation is consistent and easily understandable by other developers.
• Interoperability: Many tools and platforms support OpenAPI, making it easier to integrate with other systems and services.
• Documentation: OpenAPI provides a clear, human-readable format for API documentation, making it easier for others to understand and use your API.
• Code Generation: You can use OpenAPI specs to generate client libraries and server stubs, streamlining your development process.

Now, let's explore how to make this conversion happen!

Use postman-to-openapi: A Step-by-Step Guide

The postman-to-openapi npm package is a powerful tool for converting Postman collections to OpenAPI 3.0 specifications. Here's a step-by-step guide on how to use it:

Step 1: Install postman-to-openai  Package via npm

First, you'll need to install the package. Open your terminal and run:

npm install postman-to-openapi

Or if you prefer yarn:

yarn add postman-to-openapi

Step 2: Use postman-to-openai in Node.js

Once installed, you can use the package in your Node.js project. Here's a simple example:

const postmanToOpenApi = require('postman-to-openapi')

const postmanCollection = './path/to/your/collection.json'
const outputFile = './output/openapi.yml'

async function convertCollection() {
  try {
    const result = await postmanToOpenApi(postmanCollection, outputFile, {
      defaultTag: 'General'
    })
    console.log(`OpenAPI specs: ${result}`)
  } catch (err) {
    console.error('Conversion failed:', err)
  }
}

convertCollection()

This script will convert your Postman collection to an OpenAPI 3.0 YAML file.

Step 3: Customized Usage of postman-to-openai

The postman-to-openapi package offers several options to customize your conversion. Here are some useful ones:

• defaultTag: Set a default tag for all operations (default: 'default').
• outputFormat: Choose between 'yaml' or 'json' (default: 'yaml').
• includeAuthInfoInExample: Include auth info in examples (default: false).

Let's modify our script to use these options:

const postmanToOpenApi = require('postman-to-openapi')

const postmanCollection = './path/to/your/collection.json'
const outputFile = './output/openapi.json'

async function convertCollection() {
  try {
    const result = await postmanToOpenApi(postmanCollection, outputFile, {
      defaultTag: 'MyAPI',
      outputFormat: 'json',
      includeAuthInfoInExample: true
    })
    console.log(`OpenAPI specs: ${result}`)
  } catch (err) {
    console.error('Conversion failed:', err)
  }
}

convertCollection()

This script will output a JSON file with auth info included in examples and all operations tagged as 'MyAPI'.

What If I Do Not Want to Use postman-to-openai Package?

While the postman-to-openapi package is great for straightforward conversions, sometimes you might need more control or have specific requirements. Let's explore some advanced techniques.

Option 1. Use APIDog for Postman to OpenAPI Conversion

APIDog is another excellent tool that can help you convert Postman collections to OpenAPI format. Here's a quick guide on how to use it:

1. Log into APIDog and navigate to the "Settings" menu.
2. Select "Import" from the options.
3. Choose the Postman collection file you want to import. APIDog will import and convert your collection, allowing you to view and edit the resulting API documentation.

4. Click on the Export Data button, and choose to export to OpenAPI 3.0 Format.

But wait, APIDog isn't merely a converter for Postman Collections to OpenAPI format. It is an easy-to-use alternative that makes you forget about paying for Postman Enterprise.

APIDog offers additional features like API testing and mock servers, making it a comprehensive solution for API development and documentation. Here is what you get from APIDog instead of subscribing for Postman for $19/month:

• Unlimited API Creation
• No Flow Restrictions and Unlimited Collection Runner Runs
• Unlimited API Calls
• Unlimited API Mock Server Calls

These are all available in the APIDog Free Version!

Besides, for merely $9/month, you can access all the features for Postman Profesional Plan that would cost you $39/month!

Option 2. Use the Postman API for Conversion

Postman itself offers an API that can transform collections to OpenAPI format. Here's how you can use it:

1. Get your Postman API key from your account settings.
2. Use the following curl command (replace placeholders with your actual values):

curl --location --request GET 'https://api.getpostman.com/collections/{{collectionId}}/transformations' \
--header 'Content-Type: application/json' \
--header 'x-api-key: {{postman-api-key}}'

1. The response will contain the OpenAPI specification. You can save this to a file for further use.

Option 3. Online Tools for Postman to OpenAPI Conversion

If you prefer a quick, no-code solution, you can use some online tools for quick conversion. Here's how to use it:

1. Pick from one of the free online tools available.
2. Upload your Postman collection JSON file or paste the collection URL.
3. Click "Convert" and download the resulting OpenAPI specification.

This method is great for one-off conversions or when you don't want to set up a development environment.

How to Convert Postman to OpenAPI without Hassles: Tips and Best Practices

Even with the best tools, you might encounter some hiccups. Here are some common issues and their solutions:

• Splitting Collections: Divide large collections into smaller, more manageable parts. This approach allows for easier conversion and maintenance of the resulting OpenAPI specifications.
• Using Folders: Organize your Postman collection using folders to create a logical structure. This will help in generating a well-organized OpenAPI specification and make it easier to navigate.
• API Transformer: Utilize tools like API Transformer, which can handle large Postman collections and convert them to OpenAPI specifications efficiently.
• OpenAPI Validation: Validate your OpenAPI specification after conversion to ensure it is correct and complete. This step is crucial in identifying any issues that may have arisen during the conversion process.

So, to ensure a smooth conversion process, keep these tips in mind:

• Clean Your Postman Collection: Before conversion, review your collection for any inconsistencies or unnecessary elements.
• Use Descriptive Names: Ensure your endpoints, parameters, and responses have clear, descriptive names in Postman.
• Include Examples: Add example responses in Postman to enrich your OpenAPI documentation.
• Organize with Folders: Use folders in Postman to logically group your endpoints, which will translate to tags in OpenAPI.
• Validate the Output: After conversion, use an OpenAPI validator to ensure the resulting specification is valid.

Conclusion

Converting Postman collections to OpenAPI specifications is a crucial step in standardizing API documentation and ensuring seamless integration with other systems.

By following the steps outlined in this guide, you can efficiently convert your Postman collections and take advantage of the benefits offered by OpenAPI.

Frequently Asked Questions (FAQs)

Q: What is the primary benefit of converting Postman collections to OpenAPI specifications?
A: The primary benefit is standardization, which enables easier integration with other systems and tools.

Q: Can I use online tools for Postman to OpenAPI conversion?
A: Yes, online tools like p2o.defcon007.com and APIDog are available for converting Postman collections to OpenAPI specifications.

Q: How do I handle large Postman collections during conversion?
A: Large collections can be split into smaller parts, organized using folders, or converted using tools like API Transformer.

Q: Is it necessary to validate the OpenAPI specification after conversion?
A: Yes, validating the OpenAPI specification after conversion is crucial to ensure it is correct and complete.