JSON Repair — Fix Broken JSON Online

JSON repair identifies and corrects common syntax mistakes that cause JSON.parse() to throw a SyntaxError, without changing the underlying data. The repair process applies a series of targeted transformations before attempting to parse:

• Trailing commas — removed before closing } or ]. The JSON spec (RFC 8259) explicitly forbids trailing commas even though JavaScript allows them. This is the most common error when JSON is written or edited by hand.
• JavaScript comments — stripped before parsing. Both line comments (// ...) and block comments (/* ... */) are removed. Comments are common in configuration files but invalid in strict JSON.
• Single-quoted strings — replaced with double quotes. JSON requires all strings to use double quotes; single quotes are a JavaScript-only convention that many developers apply out of habit.
• Unquoted keys — property names without quotes (e.g., { key: "value" }) are wrapped in double quotes to produce valid JSON. Unquoted keys are valid in JavaScript object literals but not in JSON.

After all transformations are applied, the tool attempts JSON.parse() on the result. If parsing succeeds, the repaired and formatted JSON is shown alongside a summary of every change that was applied. If the input is too structurally broken to repair automatically — missing brackets, missing colons, fundamentally malformed input — the tool reports what it found so you can make targeted manual corrections.

A developer copies a JavaScript object literal from their codebase intending to use it as an API request body or config file, but it contains several issues that make it invalid JSON:

{
  // User profile
  name: 'Alice',
  age: 30,
  city: 'NYC',
  active: true,
}

This input has four problems: a JavaScript line comment, single-quoted strings, unquoted keys, and a trailing comma after the last property. The repair tool fixes all four in one pass:

{
  "name": "Alice",
  "age": 30,
  "city": "NYC",
  "active": true
}

The comment is stripped, single quotes become double quotes, all keys gain quotes, and the trailing comma after "active" is removed. The result passes JSON.parse() cleanly and retains all the original values. This pattern is extremely common when developers copy JavaScript config objects and need to use them in an API body, a .json config file, a database seed script, or a Postman / curl request.

Automated repair works best for the class of errors introduced by manual editing or copying from JavaScript source code. Trailing commas, comments, single quotes, and unquoted keys are all artifacts of JavaScript syntax that developers habitually write but that the stricter JSON spec rejects. These are mechanical, unambiguous fixes — the repair tool can apply them reliably without any risk of changing the intended data.

Repair cannot fix structural problems: mismatched brackets or braces, missing colons between keys and values, duplicate keys, two adjacent values without a separating comma, or keys without values. These require understanding the intended structure of the data, which no automated tool can infer reliably. For these cases, the error message will indicate the approximate location of the problem so you can make a targeted manual correction.

After repairing, always verify that the output is semantically correct — that every value is what you intended, not just that the JSON parses successfully. The repair tool reports every transformation it applies so you can review each change. A repair that silently alters a key name or value would be more dangerous than one that fails loudly, so no speculative changes are ever made to data values.