JSON Repair

Fix broken JSON in one paste

Copied JSON out of a log file, a JavaScript source, a Python print, or an LLM answer and your parser rejects it? Paste it above and this tool rebuilds it as valid JSON. It is a tolerant parser, not a find-and-replace: the input is re-parsed token by token and re-serialized, so the output is always syntactically valid JSON. Everything runs locally in your browser — nothing is uploaded.

What it fixes

• Trailing commas — [1, 2, 3,] → [1, 2, 3]
• Single quotes, backticks, and smart quotes — {'a': 'b'} → {"a": "b"}
• Unquoted keys and values — {name: John Smith} → {"name": "John Smith"}
• Missing commas — {"a": 1 "b": 2} → {"a": 1, "b": 2}
• Comments — // line and /* block */ comments are removed
• Markdown fences — the JSON inside ```json … ``` is extracted (prose around it is ignored)
• Truncated JSON — unclosed strings, arrays, and objects are closed ({"a": [1, 2 → {"a": [1, 2]})
• Python & JS literals — True/False/None → true/false/null; undefined, NaN, and Infinity become null
• Raw newlines and tabs inside strings — escaped to \n / \t
• Mismatched brackets — [1, 2} → [1, 2]

Worked example

Input:

{'name': 'John', age: 30, // legacy record
 tags: ['admin' 'ops'],}

Repaired output (2-space indent):

{
  "name": "John",
  "age": 30,
  "tags": [
    "admin",
    "ops"
  ]
}

Limits and edge cases

• Syntax only, not semantics — the repair makes the text parse; it cannot know what a half-missing document was supposed to contain. Review the output before trusting it for anything critical.
• Nesting is capped at 200 levels; deeper input returns an error instead of a repair.
• Duplicate keys keep the last value, and object key order is otherwise preserved.
• Unescaped double quotes inside a double-quoted string end the string early — escape those by hand ("he said \"hi\"").
• NaN and Infinity have no JSON form and become null; numbers larger than 64-bit integers are converted to floating point.
• Several top-level values (e.g. newline-delimited JSON) are wrapped into one array.
• Text after the first complete value is ignored unless it looks like another JSON value.

FAQ