JSON

JSON Cheat Sheet

A compact reference for JSON syntax, types, and the FreeToolMate tools that format, validate, and inspect JSON privately in your browser.

Basic structure

{
  "name": "Ada",
  "active": true,
  "score": 42,
  "tags": ["json", "api"],
  "profile": null
}

Types

• Object — curly braces with "key": value pairs
• Array — square brackets of values
• String — double quotes only
• Number — no leading zeros
• Boolean — true / false
• null — explicit empty value

Common syntax errors

• Trailing commas after the last item
• Single quotes instead of double quotes
• Unquoted keys
• Comments (// or /* */ are not valid JSON)
• NaN or undefined values

FreeToolMate JSON tools

• JSON Beautify / Formatter — pretty-print or minify
• JSON Viewer — collapsible tree
• JSON Schema Validator — validate structure
• JSON Compare — match paths across two documents
• JSON Diff — added, removed, changed
• JSONPath Tester — query nested values

All articles · JSON Tools hub