About PolyJSON

Why PolyJSON Exists

Every developer has been there: you need to compare multiple JSON configuration files across Dev, Staging, and Production, but your diff tool only handles two files at a time. You end up juggling multiple tabs, copying values into spreadsheets, or uploading sensitive configs to online tools. PolyJSON was built to solve this problem once and for all.

PolyJSON lets you compare multiple JSON files locally on your machine — 3, 4, or even 5 files at once. Whether you're auditing environment configs, validating API responses, or reviewing infrastructure-as-code templates, PolyJSON shows you exactly where your files diverge without uploading anything.

Compare JSON Locally — No Uploads

PolyJSON runs entirely on your local machine. All JSON comparison, diffing, and processing happens in your browser. Your data is never sent to any server, never logged, and never stored anywhere except your own device (via IndexedDB for the optional save feature).

We believe developer tools should respect your data. Configuration files often contain sensitive information — API keys, database URLs, internal service names. PolyJSON ensures that information never leaves your machine.

Technology

PolyJSON is built with modern web technologies:

  • Next.js — React framework for fast, SEO-friendly pages
  • React 19 — Latest React with concurrent features
  • Tailwind CSS v4 — Utility-first styling with a Material Design 3 dark theme
  • IndexedDB — Browser-native storage for saving your JSON files locally
  • diff library — Line-level and word-level diffing for precise comparison

The entire application is statically exported — no server-side rendering, no API routes, no backend. This makes PolyJSON fast, reliable, and deployable anywhere.

Open and Free

PolyJSON is free to use with no account required, no premium tier, and no feature gates. The site is supported by non-intrusive advertising. We believe developer tools should be accessible to everyone.

Get Started

Ready to compare your JSON files? Open the tool and start comparing in seconds. Have questions? Check out our FAQ or read our guides.