JSON Repair

How to repair JSON

1. Paste the broken text or press Open file. The Report tab shows the first error.
2. Press Repair JSON or Ctrl + Enter. The editor now holds valid JSON, indented with your Indent setting.
3. Check the result before you use it.

If repair fails, the editor stays as it was and a message says where it gave up.

Fix JSON from an LLM

Model output breaks in predictable ways: a Markdown code fence, Python literals, trailing commas, ... in place of the rest of a list, and an ending cut off by the token limit. This reply has all of them:

```json
{
  "product": "Trail Runner 2",
  "sentiment": 'positive',
  "pros": ["grip", "weight",],
  "cons": ["sizing runs small", ...],
  "would_recommend": True,
  "rating": 4.5
```

Repair JSON returns:

{
  "product": "Trail Runner 2",
  "sentiment": "positive",
  "pros": [
    "grip",
    "weight"
  ],
  "cons": [
    "sizing runs small"
  ],
  "would_recommend": true,
  "rating": 4.5
}

Copy only the fenced block: a sentence before or after the fence is kept as an extra string, and the result becomes an array.

What JSON repair fixes

• Single quotes, curly quotes and unquoted keys
• Missing commas, and trailing commas such as {"a": 1,}, which Chrome reports as Expected double-quoted property name in JSON
• // and /* */ comments (see can JSON have comments)
• Python’s True, False and None
• Unclosed brackets and strings in cut-off output, where Unterminated string in JSON is the usual symptom
• Raw line breaks inside strings, which become \n
• JSONP wrappers like callback({...}), MongoDB types like NumberLong(2), and escaped JSON like {\"id\": 1}
• One object per line (NDJSON), which becomes an array

The engine is the open-source jsonrepair library (import { jsonrepair } from 'jsonrepair'). This page strips a Markdown fence before it runs and checks the output with the strict parser of the JSON validator.

What it cannot fix

• Missing data. Cut-off text is closed, not completed: {"id": 812, "priority": "low", "summ comes back with "summ": null.
• Windows paths. In "C:\data\new", the invalid \d loses its backslash and \n becomes a line break: "C:data\new". Double the backslashes first.
• Guesses. NaN and Infinity become strings, undefined becomes null, and 02134 becomes the string "02134". Check that this suits your code.

Common JSON errors explains each parser message.