JSONパーサー / 整形ツール

Online JSON Parser & Formatter

JSON (JavaScript Object Notation) is the most common data exchange format. A JSON parser validates your JSON, pretty-prints it with indentation, and highlights syntax so you can spot errors instantly.

Features

• Real-time validation with 150ms debounce as you type
• Collapsible tree view — explore nested objects/arrays with +/− toggles
• Format / Minify — 2-space, 4-space, or tab indentation, or strip whitespace
• Error location — shows "line N, col M" for parse failures
• Lenient mode auto-recovery — fixes unescaped control characters, wrap-split tokens, trailing commas, and comments
• Recovery highlight — auto-recovered values get a 🟥 red outline so you can spot what changed
• Syntax highlighting — keys, strings, numbers, booleans, null colored distinctly
• Copy / Download — copy formatted output or save as .json file

Lenient mode — auto-recovery for broken JSON

JSON copied from chat apps, email clients, or terminals often contains accidental line breaks that break JSON.parse. This tool auto-recovers 4 common cases:

1. Control chars inside strings (\n, \t) → replaced with spaces
2. Line breaks inside tokens (e.g. 847\n521, fal\nse) → rejoined
3. Trailing commas → removed
4. Comments (//, /* */) → stripped (URLs preserved)

When recovery applies, a yellow warning banner appears and recovered values are outlined in red.

Privacy: 100% client-side

Your JSON is never sent to any server. All parsing happens in your browser. Safe for JSON containing API keys, passwords, or sensitive customer data.

Common parse errors

• Unexpected token: missing quotes around keys, or missing comma/colon
• Unexpected end of input: unclosed {} or []
• Trailing comma after the last item — not allowed in strict JSON
• Single quotes — JSON requires double quotes for strings

JSON syntax cheatsheet

• Keys must be strings wrapped in double quotes
• Values: string, number, boolean (true/false), null, object {}, array []
• No comments (// or /* */) in strict JSON