Is this JSON validator free?

Yes — completely free with no signup. All validation runs in your browser; no data is sent to any server.

What does 'Unexpected token' mean in JSON?

It means the parser found a character it didn't expect — often a single quote (should be double), a trailing comma, or a JavaScript-only value like undefined.

Can I validate large JSON files?

Yes — there are no size limits. The validator processes your JSON entirely in the browser.

Does the validator show the line number of the error?

Yes — when a syntax error is detected, the exact line number and column are shown alongside a plain-English hint for how to fix it.

JSON Validator Online — Free & Instant

JSON Input

Paste any JSON — validator checks syntax & structure

Validation Result

Syntax check, structure warnings & type breakdown

Paste JSON and click Validate

Checks syntax, structure, and value types

JSON Validator

How to Use

1Paste your JSON string into the input area. The border color indicates the current state (green = valid, red = invalid).
2Click 'Validate JSON' to run a full syntax and structure check.
3If there is a syntax error, the exact line and column number is shown alongside the raw error message.
4A 'How to Fix' hint card provides a plain-English explanation of the most common cause for that error.
5If the JSON is valid, a type distribution breakdown (objects, arrays, strings, numbers, booleans, nulls) is shown.
6Structure warnings (like deep nesting > 10 levels) are shown separately from syntax errors.

Practical Applications

API Development

Validate request and response payloads before sending or processing them, catching malformed JSON early in the development loop.

Config File Verification

Check that JSON config files (package.json, .eslintrc, appsettings.json) are syntactically correct before deploying.

Data Pipeline QA

Quickly verify that exported data from databases, spreadsheets, or third-party systems is valid JSON before importing.

Learning JSON Syntax

Use the validator as a learning tool — experiment with JSON syntax and get immediate, specific feedback on any mistakes.

Frequently Asked Questions

QWhat makes JSON invalid?

Common causes include: using single quotes instead of double quotes, trailing commas after the last item in an array or object, unquoted object keys, using JavaScript keywords (undefined, NaN, Infinity) which are not part of the JSON spec, and unclosed brackets or braces.

QWhat is the difference between JSON validation and JSON formatting?

Validation checks that your JSON is syntactically correct according to the spec. Formatting (pretty printing) takes valid JSON and makes it more readable with indentation. You must validate before formatting — formatting invalid JSON will fail.

QDoes this validator check for duplicate keys?

The JSON specification technically allows duplicate keys but most parsers keep only the last value. The native browser parser used here does not throw an error for duplicates, so they will not be flagged as errors but may cause silent data loss.

QIs the JSON validator free to use?

Yes — completely free, no signup, no limits. All validation happens in your browser using the native JavaScript engine. No data is sent to any server.

QWhat does 'Unexpected token' mean in a JSON error?

It means the parser encountered a character it did not expect at that position. Common causes: a single quote (should be double), a trailing comma, an unquoted key, or a JavaScript value like undefined or NaN that is not part of the JSON spec.