How to Validate JSON in JavaScript

There's no need for a library to validate JSON in JavaScript — the language has it built in. The trick is knowing how to use JSON.parse correctly and how to read the errors it throws.

The reliable way: JSON.parse in a try/catch

JSON.parse throws a SyntaxError on invalid input, so wrap it:

function isValidJSON(str) {
  try {
    JSON.parse(str);
    return true;
  } catch {
    return false;
  }
}

If you also want the parsed value (you usually do), return it instead of a boolean:

function tryParseJSON(str) {
  try {
    return { ok: true, value: JSON.parse(str) };
  } catch (err) {
    return { ok: false, error: err.message };
  }
}

Reading the error

Modern engines point at the problem. A message like Unexpected token } in JSON at position 42 tells you the character offset — you can turn that into a line and column by counting newlines up to that index, which is exactly what a good formatter shows you visually.

Common mistakes

• Single quotes — JSON requires double quotes for keys and strings.
• Trailing commas — [1, 2, 3,] is invalid JSON (valid JS, invalid JSON).
• Unquoted keys — { name: "x" } is a JS object literal, not JSON.
• undefined / functions / comments — none are allowed in JSON.
• Confusing "valid JSON" with "the shape I expect" — JSON.parse only checks syntax. Validate the structure separately (or with a schema).

Try it

Paste your JSON to validate and format it — invalid input shows the exact line and column of the problem, so you can fix it fast.