json-repair-engine

A JSON repair engine built for LLM-generated output. Fixes common syntax errors and produces a structured diagnostic report for every repair.

Problem

LLMs frequently emit malformed JSON — trailing commas, Python-style literals (True, False, None), unquoted keys, unterminated structures, comments, single-quoted strings, and more. Standard JSON parsers reject these outright, forcing brittle regex workarounds in every integration.

Most repair tools fix silently. json-repair-engine explains every change.

Features

• Python literals — True → true, False → false, None → null, undefined → null
• Trailing commas — strips commas before } and ]
• Unquoted keys — quotes bare identifiers in objects ({key: "val"} → {"key": "val"})
• Single-quoted strings — converts 'string' to "string"
• Comments — strips //, /* */, and # comments
• Missing commas — inserts commas between adjacent values ([1 2 3] → [1, 2, 3])
• Extra commas — collapses doubled commas ([1,,2] → [1,2])
• Unterminated structures — closes missing braces, brackets, and strings
• Trailing garbage — extracts valid JSON from text with extra content before/after
• Markdown fences — extracts JSON from ```json ... ``` blocks
• Hex literals — 0xFF → 255
• String-aware repair — all replacements skip quoted string contents
• Structured diagnostics — every repair includes type, position, original, replacement, and message
• Confidence scoring — each fix has a penalty; aggregate score in the report
• Zero dependencies — standard library only

Installation

pip install json-repair-engine

Usage

Python API

from jsonrepair import loads

data, report = loads('{"ok": True, "items": [1, 2,],}')

print(data)              # {'ok': True, 'items': [1, 2]}
print(report.valid)      # True
print(report.repaired)   # True
print(report.confidence) # e.g. 0.97
print(report.repair_count)  # 3

for fix in report.fixes:
    print(f"[{fix.type}] at position {fix.position}: {fix.message}")

CLI

$ jsonrepair response.json
{
  "ok": true,
  "items": [1, 2]
}

--- Repair Report ---
{
  "valid": true,
  "repaired": true,
  "confidence": 0.97,
  "repairs": 3
}

API Reference

loads(text: str) -> tuple[dict | list, RepairReport]

Parse and repair a JSON string. Returns the parsed data (object or array) and a repair report.

RepairReport

Fix

Fix types

License

MIT