How to Validate JSON Online (with Exact Line & Column Errors)
Updated
"Is this JSON valid?" is usually the first question when an API call fails, a config file won't load, or JSON.parse throws. A JSON validator answers it in seconds — and a good one tells you exactly where the problem is, not just that one exists.
The Advanced JSON Toolkit validates as you type and reports the precise line and column of the first syntax error, entirely in your browser.
Step-by-step
Open the JSON validator
Go to the Advanced JSON Toolkit homepage — the editor doubles as a validator.
Paste or upload your JSON
Paste the document, drop in a .json file up to 10MB, or load it from a URL. Validation runs automatically on every change.
Read the error message
If the JSON is invalid, the toolkit shows the parser's error message with the exact line and column where parsing failed, so you can jump straight to the problem.
Fix and re-check
Correct the reported issue and the validator re-runs instantly. When the error banner disappears, the document is valid JSON per RFC 8259.
What "valid JSON" actually means
JSON is defined by RFC 8259 (and ECMA-404). A valid document is a single JSON value — object, array, string, number, true, false, or null — where all strings and keys use double quotes, no trailing commas appear, and no comments exist. These rules are stricter than JavaScript object-literal syntax, which is the single biggest source of confusion.
Validators built on the browser's native JSON.parse — like this one — apply exactly the same rules your production code does, so a green result here means JSON.parse, Python's json.loads, and every standards-compliant parser will accept it.
The five errors that cause 90% of failures
Almost every invalid document fails for one of these reasons: single quotes instead of double quotes; a trailing comma after the last item; a missing closing brace or bracket (often from a truncated copy-paste); comments, which JSON forbids; or JavaScript-only values like undefined, NaN, or Infinity.
Each of these produces a distinctive parser message. The dedicated guides below walk through the two most common ones character by character.
Validating without uploading your data
Payloads you validate are often the ones you least want to share: production API responses, auth tokens, customer data. This validator runs entirely client-side — nothing is transmitted, logged, or stored, and it keeps working offline once the page has loaded.
Try it now
Paste your JSON into the free toolkit — validate, beautify, minify, and explore it without your data ever leaving the browser.
Open the JSON ToolkitFrequently asked questions
How do I check if JSON is valid without writing code?
Paste it into an online validator like the Advanced JSON Toolkit. It parses the document instantly and either confirms it is valid or shows the exact line and column of the first syntax error.
Why does my JSON work in JavaScript but fail validation?
JavaScript object literals allow single quotes, unquoted keys, trailing commas, and comments — JSON allows none of these. A validator checks the stricter JSON standard (RFC 8259), which is what APIs and parsers expect.
Does the validator check JSON Schema?
No — it checks syntax (is this well-formed JSON?), not schema conformance (does it have the right fields and types?). Syntax validation is the necessary first step before any schema check.