I Built a Fast, Privacy-First JSON Formatter with Next.js

As a developer, I work with JSON almost every day.

Whether it's debugging APIs, inspecting responses, or formatting configuration files, I constantly found myself opening online JSON formatter tools.

After trying dozens of them, I noticed a few recurring problems:

1. Some were cluttered with too many ads.
2. Some felt slow when formatting large JSON files.
3. Some uploaded data to a server, which isn't ideal when working with sensitive information.
4. Many had outdated interfaces and poor mobile support.

So I decided to build my own.

Goals

Before writing any code, I made a list of what I wanted:

• Fast performance
• Clean and modern interface
• Works entirely in the browser
• No login required
• Mobile-friendly
• Free to use

Tech Stack

I built the project using:

• Next.js
• React
• TypeScript
• Tailwind CSS
• Vercel for deployment

The goal wasn't just to create another JSON formatter—it was to build a growing collection of useful developer tools.

Features

The formatter currently supports:

• JSON formatting
• JSON validation
• Pretty printing
• Error detection
• Instant formatting
• Responsive design

Since everything runs in the browser, your JSON stays on your device instead of being uploaded to a server.

Challenges

One challenge was handling invalid JSON gracefully.

Instead of showing a generic error, I wanted the tool to clearly indicate when the JSON couldn't be parsed so developers could fix it quickly.

Performance was another focus. Large JSON files should still feel responsive without unnecessary loading.

What's Next

This is only the beginning.

I'm planning to add many more developer tools, including:

• JWT Decoder
• JWT Generator
• Regex Tester
• UUID Generator
• XML Formatter
• YAML Formatter
• SQL Formatter
• URL Encoder/Decoder
• Markdown Preview

The goal is to create a fast, simple collection of tools that developers can rely on every day.

I'd Love Your Feedback

1. If you're a developer, I'd really appreciate your feedback.
2. What features do you usually look for in a JSON formatter?
3. What tools do you find yourself using most often?
4. Your suggestions will help shape future updates.

If you'd like to try the formatter, you can find it here:

https://www.devynta.com/json-formatter

Thanks for reading, and happy coding!