JSON Formatter & Validator は何をしますか？
JSON Formatter & Validator はブラウザ上でデータを整形・検証するツールで、結果と制限を明確に示します。 検証済みの機能： Strict RFC 8259 parsing, 2-space, 3-space, 4-space, or tab indentation, JSON5 repair, Lossless large-number mode, Searchable tree view, Local file input and optional draft restore.
Choose strict, repair, or lossless behavior deliberately
Use strict formatting for API payloads, Repair JSON5 only for known relaxed input, Tree view for inspection, and Lossless numbers when every numeric digit must survive.
使い方
- Paste, type, or open one JSON document.
- Choose indentation, key sorting, minification, lossless numbers, or Tree view.
- Correct any reported syntax location, optionally repair JSON5 syntax, then copy or download formatted.json.
実際の入出力例
Format one compact object
入力
{"project":"KitLumi","local":true}出力
{
"project": "KitLumi",
"local": true
}The parser validates the document first and then prints the same parsed values with two-space indentation.
一般的なエラーと対処
| 症状 | 原因 | 対処 |
|---|---|---|
| Parsing stops near a property name. | The key uses single quotes or no quotes. | Wrap every property name and string in double quotes. |
| A large integer changes after formatting. | Standard mode uses JavaScript Number and the value exceeds safe-integer precision. | Enable Lossless numbers or represent identifiers as JSON strings. |
Strict JSON, explicit repair, and numeric precision
このツール固有の制限： Strict mode rejects comments, trailing commas, single quotes, NaN, Infinity, and undefined. Repair JSON5 converts supported extensions; Lossless numbers keeps exact numeric text.
標準と実装の参考資料
- RFC 8259 — JSON (opens in a new tab)Defines the JSON grammar and value types.
- MDN — JSON.parse() (opens in a new tab)Documents the browser parser used by the page.
JSON Formatter — FAQ
Does the JSON Formatter upload data?
No. Parsing, formatting, key sorting, and minification run in the current browser tab.
Does it accept JSON5 or comments?
Strict formatting rejects JSON5 extensions, but Repair JSON5 can deliberately convert comments, trailing commas, single quotes, and unquoted keys to strict JSON.
Can it preserve very large numbers?
Yes. Enable Lossless numbers to keep the original JSON number text instead of rounding through JavaScript Number.
更新内容
実質的な更新： JSON Formatter: Added file input, three-space indentation, JSON5 repair, lossless-number mode, searchable tree view, undo and redo, auto-format control, opt-in draft restore, fullscreen, and printing.