llm-json-parse

Extract and repair JSON from noisy LLM text output. Zero dependencies, TypeScript-first.

LLMs rarely return perfectly clean JSON. You usually get things like:

Sure! Here's the data you asked for:

```json
{
  "name": "Ada",
  "tags": ["a", "b",],
}
```

Let me know if you need anything else!

llm-json-parse strips the fences and prose, extracts the JSON span, and repairs common mistakes (trailing commas, single quotes, unquoted keys) so JSON.parse doesn't blow up.

Install

npm install llm-json-parse

Usage

import { parseLLMJson, safeParseLLMJson } from "llm-json-parse";

const text = await callYourLLM();

// Throws LLMJsonParseError if it truly can't be parsed
const data = parseLLMJson<{ name: string; tags: string[] }>(text);

// Or, never throws:
const result = safeParseLLMJson(text);
if (result.success) {
  console.log(result.data);
} else {
  console.error(result.error);
}

What it handles

• Markdown code fences (```json ... ```, or plain ``` ... ```)
• Extra prose before/after the JSON ("Sure, here's the result: {...} Let me know!")
• Trailing commas ({"a": 1,})
• Single-quoted strings ({'a': 'b'})
• Unquoted object keys ({a: 1})
• Braces/brackets inside string values (won't confuse the extractor)

API

parseLLMJson<T>(input: string, options?: ParseOptions): T

Parses and returns the JSON value. Throws LLMJsonParseError if parsing fails.

safeParseLLMJson<T>(input: string, options?: ParseOptions): SafeParseResult<T>

Never throws. Returns { success, data, error }.

ParseOptions

{ repair?: boolean } // default: true — set false to disable lenient repairs

License

MIT