JSON Repair & Malformed Syntax Fixer

MALFORMED JSON INPUT

Broken / LLM Output JSON

REPAIRED VALID JSON

Valid Repaired Output

JSON Syntax Repair Guide — Fixing Truncated LLM Outputs

JSON (JavaScript Object Notation) requires strict formatting rules. Malformed JSON payloads cause server parsers to throw runtime syntax errors. This tool automatically cleans and repairs invalid JSON structure.

Common Syntax Errors Repaired

Single Quotes to Double Quotes: {'key': 'val'} → {"key": "val"}
Unquoted Object Keys: {name: "John"} → {"name": "John"}
Trailing Commas: [1, 2, 3,] → [1, 2, 3]
Python Literals: None → null, True → true, False → false

Related Developer Tools

Validate JSON schemas with the JSON Schema Validator, format JSON payloads using the JSON Formatter, or convert JSON to TypeScript interfaces with the JSON to TypeScript Generator.

Frequently Asked Questions

Common questions about this tool.

How does the JSON Repair tool work? ▼

The tool uses deterministic string transformation rules to automatically convert unquoted keys (`{name: "val"}`), single quotes (`{'key': 'val'}`), trailing commas (`[1, 2,]`), and missing closing brackets into valid JSON.

Why do LLM API outputs frequently contain broken JSON? ▼

LLMs streaming responses may truncate near token limits or output Python-like syntax (single quotes, `None` instead of `null`, `True` instead of `true`), breaking standard `JSON.parse()`.

Does this tool support repairing truncated JSON arrays? ▼

Yes! The repair engine detects missing closing brackets `]` and braces `}` and appends them to form valid JSON.

Is my JSON data kept private? ▼

100% private. All repair operations run locally in your browser using client-side JavaScript.

Can I copy the repaired JSON output? ▼

Yes! Click the "Copy Repaired JSON" button to copy clean, formatted JSON directly to your clipboard.