How to Comment in a JSON File: Workarounds and Best Practices

How to Comment in a JSON File

JSON (JavaScript Object Notation) is a lightweight data-interchange format that is easy for humans to read and write, but it lacks native support for comments. If you’ve ever wanted to document or annotate your JSON file, you’ve probably faced this limitation. This blog will explore why JSON doesn’t support comments, common workarounds, and best practices to keep your files clean and maintainable.

What is JSON and Why Comments Are Not Supported

JSON was designed to be a simple, data-only format, which is why it does not include support for comments as part of its specification. Created by Douglas Crockford, JSON was meant to be an efficient format for transmitting data between a server and a client. Its strict syntax rules keep it lightweight and easy to parse by machines.

The omission of comments is intentional, as the JSON specification prioritizes simplicity and universality. Adding comments could complicate parsing and introduce potential misuse, making JSON less efficient for its primary purpose: data exchange.

Why You May Want to Add Comments to a JSON File

Despite the lack of native comment support, developers often feel the need to include comments in JSON files to provide context or instructions. For instance, configuration files often benefit from notes to explain various fields, especially when multiple developers are working on the same project.

Comments can also help during debugging by highlighting what specific fields are intended for. However, since JSON parsers reject invalid syntax, including comments in the traditional sense (e.g., // or /* */) will cause parsing errors.

Workarounds for Adding Comments to JSON Files

While JSON itself doesn’t support comments, there are practical workarounds you can use to include contextual information without breaking the file’s structure.

1. Using a _comment key: Add a dedicated key to include notes in the JSON object.
2. External documentation: Maintain separate documentation for JSON structure and field explanations.
3. Temporary modifications: Use inline notes in a local copy of the JSON file for debugging purposes, ensuring these are removed before production.

How to Use a _comment Key for Adding Notes

A common approach to add comments in JSON files is by including a dedicated _comment key with explanatory text. Here’s an example:

{

  "_comment": "This is a configuration file for the app",

  "appName": "MyApp",

  "version": "1.0.0",

  "features": {

    "_comment": "Enable or disable features individually",

    "featureA": true,

    "featureB": false

  }

}

Best Practices:

• Use consistent naming for comment keys, such as _comment or description.
• Avoid embedding lengthy explanations that could clutter the file.
• Clearly associate comments with the fields they explain.

Limitations:

• Parsers and tools will still treat _comment as regular data, potentially increasing file size.
• Some teams might view this as a deviation from JSON’s minimalist philosophy.

Tools and Libraries That Support JSON Comments

Some tools and parsers allow extended JSON syntax with comments for flexibility during development.

1. JSON5: JSON5 extends JSON syntax to include features like comments. Example:

// This is a comment in JSON5

{

  "key": "value"

}

2. Tools like Prettier or JSONLint: These tools can help validate JSON files while ignoring non-standard elements like comments during development.
3. YAML: If you need comments and flexibility, consider using YAML instead of JSON. YAML supports comments with # and is often used for configuration files.

The Importance of Stripping Comments for Production

When using commented JSON files, it’s essential to strip out the comments before deploying to ensure compatibility with standard parsers.

Tools for Comment Removal:

• Use scripts or tools like jq to clean JSON files:
• jq 'del(._comment)' input.json > output.json

Automate in CI/CD Pipelines:

• Integrate comment removal into your build process to ensure only valid JSON files are deployed.

By doing this, you maintain the readability of JSON during development while ensuring production-ready files adhere to the JSON specification.

Alternatives to Comments: Keeping JSON Files Clean and Clear

Instead of relying on comments, there are other strategies to make your JSON files self-explanatory and easier to understand:

1. Use descriptive keys and values: Avoid ambiguous names like val1; instead, use userName or accessLevel.
2. Structure data for readability:

{

  "user": {

    "name": "John Doe",

    "role": "admin"

  }

}

3. Leverage schemas: Use JSON Schema to define the structure, types, and purpose of your data, and share this schema with your team.
4. Document externally: Maintain a README or wiki explaining the purpose and structure of your JSON files.

Conclusion

While JSON’s simplicity is one of its strengths, the lack of comment support can sometimes pose challenges for developers. Workarounds like _comment keys, JSON5, and external documentation provide effective ways to add context without violating the JSON specification.

By following best practices and automating the removal of non-standard elements for production, you can balance clarity and maintainability in your JSON files. Share your experiences or favorite tools for handling JSON comments in the comments section below!