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JSON Fixer

Paste broken or invalid JSON and get it fixed in one click. The fixer automatically repairs the most common JSON mistakes — trailing commas, single quotes, bare keys, Python literals, and JS comments.

Last updated: May 21, 2026

Client-Side Processing
Input Data Stays on Device
Instant Local Execution

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What is JSON Fixer?

JSON is strict about syntax: no trailing commas, no single quotes, no comments, no unquoted keys. But JSON is often hand-written, copy-pasted from code, or generated by tools that produce slightly non-standard output. The result is JSON that fails to parse and produces cryptic "Unexpected token" errors.

This tool automatically detects and repairs the most common JSON issues: trailing commas before closing braces or brackets, strings wrapped in single quotes instead of double quotes, bare object keys without quotes, Python-style True/False/None literals, JavaScript undefined values, and JS-style single-line or block comments. It shows you exactly what was fixed so you know what changed.

How to Use JSON Fixer

1

Paste broken or invalid JSON into the input area or click "Load Sample"

2

The fixer runs automatically and shows the fixed JSON on the right

3

A fix log appears below listing every correction made

4

If the JSON could not be fully repaired, the error message tells you what still needs fixing

5

Copy or download the fixed JSON output

Common Use Cases

  • Developers fixing JSON copy-pasted from JavaScript source code that has trailing commas or comments.
  • Python developers fixing JSON that was logged or printed with Python repr (True/False/None instead of true/false/null).
  • API engineers cleaning up JSON responses from tools that produce non-standard output.
  • Front-end developers fixing hand-written JSON config files with missing quotes or trailing commas.
  • Data engineers repairing JSON data files before loading them into databases or parsers.
  • Developers debugging API payloads that fail with "Unexpected token" errors.

Example Input and Output

A JSON object with single quotes, trailing commas, bare keys, and a JS comment is automatically fixed to valid JSON.

Broken JSON input
{
  // server config
  host: 'localhost',
  port: 8080,
  debug: True,
  tags: ['api', 'v2',],
}
Fixed JSON output
{
  "host": "localhost",
  "port": 8080,
  "debug": true,
  "tags": ["api", "v2"]
}

Privacy

All fixing runs in your browser. No data is uploaded to any server.

Fix order matters

Fixes are applied in sequence: comments first, then Python literals, single quotes, bare keys, trailing commas, missing commas. The fixer stops as soon as the result is valid — so it only applies the minimum fixes needed.

Frequently Asked Questions

What types of JSON errors can this fixer repair?
The fixer handles: trailing commas before } or ], single-quoted strings, unquoted (bare) object keys, Python literals (True → true, False → false, None → null), JavaScript undefined → null, and // line comments or /* */ block comments. It applies fixes in order and stops as soon as the JSON becomes valid.
What if the JSON still cannot be parsed after fixing?
The tool shows the partially fixed JSON with the remaining parse error. Some issues — like completely missing brackets, deeply malformed structure, or binary data — cannot be repaired automatically. Use the fix log to see what was corrected, then manually address the remaining error shown.
Why does JSON not allow trailing commas?
The JSON specification (RFC 8259) does not permit trailing commas. Most JSON parsers (JSON.parse, Python's json module, etc.) follow the spec strictly. JavaScript itself has relaxed this in array/object literals and in JSON5, but standard JSON does not.
Why does JSON not allow single quotes?
JSON requires double quotes for strings. This is defined in the JSON spec. JavaScript object literals accept single quotes, so JSON copied from JS source code often needs this correction.
Is this tool safe for sensitive data?
Yes. All fixing runs entirely in your browser using JavaScript. Your JSON is never sent to any server.
What is the difference between JSON Fixer and JSON Formatter?
JSON Formatter pretty-prints valid JSON. JSON Fixer repairs invalid JSON first, then formats it. If your JSON is already valid, use the Formatter; if you get parse errors, use the Fixer.

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