JSON Validator - Check & Fix JSON Errors Online (Free)

Catch every JSON error in seconds

Paste your JSON above and hit Validate. The checker highlights the exact line and column where the problem is, so you can fix it without hunting through hundreds of lines by hand.

No sign-up needed, no file uploads - everything runs right in your browser. Your data stays on your device.

How to use the JSON Validator

1. Paste your JSON into the editor above.
2. Click Validate (or just start typing - errors appear as you go).
3. Read the error message: it tells you the line number, column, and what went wrong.
4. Fix the highlighted spot, then validate again until you see the green Valid JSON checkmark.
5. Optionally click Format to beautify the output once it's clean.

Worked example: spotting a real error

Here is a common broken payload - a trailing comma after the last key, which most JSON parsers reject:

{
  "user": "alice",
  "role": "admin",
  "active": true,
}

The validator flags: Error on line 5, column 1: Unexpected token }. Remove the comma after true and the document turns valid instantly:

{
  "user": "alice",
  "role": "admin",
  "active": true
}

Why is my JSON invalid? Common errors and one-line fixes

Our validator points to the first error's exact line and column so you never have to guess. Fix the reported spot, validate again, and work through any remaining issues one at a time.

Validate JSON in your code (Python & JavaScript)

Sometimes you want to validate a JSON string programmatically rather than in a browser. Here's the standard way in each language.

Python - uses the built-in json module:

import json

raw = '{"user": "alice", "active": true}'  # note: true is valid JSON, not Python True

try:
    data = json.loads(raw)
    print("Valid JSON", data)
except json.JSONDecodeError as e:
    print(f"Invalid JSON at line {e.lineno}, col {e.colno}: {e.msg}")

JavaScript (Node.js or browser) - uses the native JSON.parse:

const raw = '{"user": "alice", "active": true}';

try {
  const data = JSON.parse(raw);
  console.log('Valid JSON', data);
} catch (e) {
  console.error('Invalid JSON:', e.message);
}

Both approaches throw a descriptive error you can log or surface in your UI. The online validator above does the same thing, just without writing any code.

How the validator works

The tool runs the JSON.parse algorithm - the same parser built into every modern browser - directly in your browser tab. No server ever sees your data.

When parsing fails, the engine captures the character position of the first syntax problem. The editor then scrolls to that line and underlines the offending spot. The official JSON spec at json.org (authored by Douglas Crockford) defines exactly what the parser accepts; our checker follows it strictly. You can also check the IETF RFC 8259, which is the current JSON standard.

When to use a JSON validator vs. other tools

• Validate first when you're debugging an API response that your app can't parse - find and fix the error before doing anything else.
• Format after validating to make the structure readable. Try our JSON Beautifier for pretty-printed output with adjustable indentation.
• Minify before shipping to production to reduce payload size. Our JSON Minifier strips all whitespace in one click.
• View nested data in a collapsible tree with the JSON Viewer.
• Don't use a JSON validator if your data is actually JSONC (JSON with comments) or JSON5 - those are supersets that allow comments and trailing commas. A strict validator will reject them. Check your tool's docs to see which dialect it expects.
• Converting formats? If you need to move between JSON and YAML, see our JSON to YAML Converter or the YAML to JSON Converter.

Your JSON is only ever processed in your own browser. Nothing is uploaded to our servers, so it's safe to paste API keys, tokens, or internal config while debugging - just remember to rotate any secrets after you're done.

Paste your JSON above and let the validator do the work - a green checkmark means you're good to go.