json-repair-llm

Repair broken JSON from LLM outputs. Fix trailing commas, single quotes, unquoted keys, truncated objects, missing brackets, and Python literals — all without dependencies.

The Problem

LLMs frequently return invalid JSON: trailing commas, single quotes instead of double, True/False/None instead of true/false/null, missing closing brackets from truncated output, or JSON wrapped in markdown code blocks. JSON.parse() throws. This library fixes it.

Install

npm install json-repair-llm

Quick Start

const { repair, extract } = require('json-repair-llm');

// Fix broken JSON
repair("{'name': 'Alice', 'age': 30,}")
// → '{"name": "Alice", "age": 30}'

// Extract JSON from LLM markdown output
extract("Here's the data:\n```json\n{\"x\": 1}\n```\nDone!")
// → { x: 1 }

API

repair(str)

Returns a repaired JSON string. Fixes:

• Trailing commas: {a: 1,} → {a: 1}
• Single quotes: {'a': 'b'} → {"a": "b"}
• Unquoted keys: {name: "Alice"} → {"name": "Alice"}
• Python booleans: True/False/None → true/false/null
• Missing closing brackets from truncation
• Escaped single quotes inside strings
• Comments (// and /* */)

extract(text)

Extracts and parses JSON from messy LLM output. Returns parsed object/array or null. Handles: bare JSON, ```json code blocks, JSON embedded in text.

safeParseJSON(str)

Like JSON.parse() but tries repair first. Returns { data, error }.

License

MIT