Chrome extension that auto-formats JSON when you view it in a browser tab.

• Fast, even on very long JSON pages
• Dark mode
• Syntax highlighting
• Collapsible trees, with indent guides
• Clickable URLs
• Negligible performance impact on non-JSON pages (less than 1 millisecond)
• Works on any valid JSON page – URL doesn't matter
• Buttons for toggling between raw and parsed JSON
• Parsed JSON is exported as a global variable, json, so you can inspect it in the console*

*Typing json the in console is not working since Manifest v3. If you need a workaround, paste this snippet into the console:

json = JSON.parse(document.getElementById("jsonFormatterRaw").querySelector("pre").innerText)

Some JSON documents for testing it on: https://callumlocke.github.io/json-formatter/

Option 1 (recommended) – Install it from the Chrome Web Store.

Option 2 – Install it from source (see below).

Requirements: Deno (and Node for now).

Initial setup:

• Clone repo
• Run pnpm i to get TypeScript typings for chrome (or use npm i if you prefer)
• Optional: if using VSCode and you need to mess with the Deno build scripts, install the official Deno plugin and set "deno.enablePaths": ["tasks"].

To build it:

• Run deno task build

To build and rebuild whenever files change:

• Run deno task dev

To install your local build to Chrome

• Open Chrome and go to chrome://extensions
• Enable "Developer mode",
• Click "Load unpacked",
• Select the dist folder you built above.

This is a limitation of JavaScript and therefore a limitation of JSON as interpreted by your web browser.

• Anything above Number.MAX_SAFE_INTEGER (2^53 - 1 or 9007199254740991) is adjusted down to that number.
• Anything below Number.MIN_SAFE_INTEGER (-2^53 + 1 or -9007199254740991) is adjusted up to that number.
• Extremely precise floating point numbers are rounded to 16 digits.

It's not JSON Formatter doing this, it's the native JSON.parse in V8. JSON Formatter shows you the parsed values, exactly the same as what you'll see after loading the JSON in JavaScript.

If your API endpoint really needs to represent numbers outside JavaScript's safe range, it should quote them as strings.

What you see in JSON Formatter is a representation of the parsed object/array. It's the same order you'll get with Object.keys( JSON.parse(json) ) in JavaScript.

Historically, the JavaScript standard explicitly stated that object keys can be iterated in any order, and V8 took advantage of this by moving numeric string keys (like "1" or "99999") to the top to facilitate a small performance optimisation. This V8 implementation detail has since become standardised.

For now, your best option is to just use the "Raw" button to see the raw JSON. This is what the server sent. The "Parsed" buttons represents what you'll get from JSON.parse.

In future JSON Formatter might switch from using JSON.parse to a custom parser (if performance allows) in order to detect when a value has been 'changed' by parsing and show an appropriate warning.