🚀 I Built a Free JSON Formatter — Here's What I Learned While Processing Large JSON Files in the Browser

👋 Introduction

If you've ever worked with APIs, you've probably encountered one of these situations:

A massive JSON response that's impossible to read.
An "Unexpected token" error with no clue where it occurred.
A minified JSON payload compressed into a single line.
A need to quickly validate whether your JSON is actually valid.

I ran into these problems almost every day while developing web applications.

Instead of repeatedly switching between different websites, I decided to build my own JSON Formatter as part of my developer tools platform.

Along the way, I learned a lot about browser performance, JSON parsing, and creating a better developer experience.

In this article, I'll share those lessons.

🤔 Why Do Developers Need a JSON Formatter?

Imagine receiving this API response:

{"user":{"id":101,"name":"John","address":{"city":"London","country":"UK"},"orders":[{"id":1,"amount":200},{"id":2,"amount":350}]}}

It's technically correct...

But can you quickly find the second order amount?

Probably not.

Now compare it with:

{
"user": {
"id": 101,
"name": "John",
"address": {
"city": "London",
"country": "UK"
},
"orders": [
{
"id": 1,
"amount": 200
},
{
"id": 2,
"amount": 350
}
]
}
}

💡 How JSON Formatting Works

Behind the scenes, formatting JSON is surprisingly simple.

const formatted = JSON.stringify(
JSON.parse(json),
null,
2
);

The process is:

Parse the JSON
Validate it
Convert it back with indentation

If the JSON is invalid, the parser throws an error.

🚨 Common JSON Mistakes

These are the issues I see most often.

❌ Missing comma

{
"name":"John"
"age":30
}

❌ Single quotes

{
'name':'John'
}

❌ Unmatched braces

{
"name":"John"

⚡ Performance Challenges

Formatting a small JSON file is easy.

Formatting a 20MB JSON file is a different story.

Some challenges include:

Browser freezing
High memory usage
Slow rendering
Delayed syntax highlighting

While building my formatter, I realized that handling large files efficiently requires careful optimization rather than simply calling JSON.stringify().

🛠 Features I Wanted

Instead of creating another basic formatter, I wanted something developers could actually use every day.

My checklist included:

JSON Formatting
JSON Validation
Minification
Pretty Print
Copy to Clipboard
Download JSON
Dark Mode
Mobile Friendly
Fast Performance

📈 Lessons I Learned

Building developer tools taught me that simplicity matters more than flashy design.

Developers want tools that are:

Fast
Reliable
Privacy-friendly
Easy to use
Free for common tasks

If a tool solves a problem in seconds, people come back.

💬 What Developer Tool Should I Build Next?

I'm currently expanding my developer tools platform and would love suggestions.

Ideas I'm considering:

JSON Compare
JSON to C# Class
JWT Decoder
SQL Formatter
YAML Formatter
Base64 Encoder
Image Compressor

Which one would you use the most?

Let me know in the comments.

🙌 Thanks for Reading

Thanks for taking the time to read this article.

If you're building developer tools or have ideas for features that save developers time, I'd love to hear about them.

Happy coding! 🚀

Helpful Resource:- https://toolbenchapp.com/tools/json-formatter