JSON Validator & Syntax Linter

Free online JSON Validator and Syntax Linter. Pinpoint exact error line and column numbers, fix trailing commas and unquoted keys with one-click Auto-Fix, 100% private in your browser.

JSON Validator & Syntax Linter

RFC 8259 syntax checker with line pointers and one-click auto-repair

Test Cases:

Invalid JSON Syntax

Unexpected token ']', ..."ogout", ], "time"... is not valid JSON

JSON Document Editor

10 lines • 135 chars

Developer Scenario: Locating a Hidden Trailing Comma in a 5,000-Line Config

An application crashes on startup with `SyntaxError: Unexpected token } in JSON at position 4982`. The engineer pastes the configuration to isolate the offending line.

Invalid JSON Snippet	{ "name": "production-cluster", "nodes": ["node-1", "node-2",], "timeout": 30, }
Validator Error Report	Line 3, Column 33: Trailing comma before closing bracket `]`. Line 5, Column 1: Trailing comma before closing brace `}`.
Auto-Fixed Valid JSON	{ "name": "production-cluster", "nodes": [ "node-1", "node-2" ], "timeout": 30 }

💡 One-click Auto-Fix strips illegal trailing commas and converts unquoted keys to valid RFC 8259 format in milliseconds.

How to use JSON Validator & Syntax Linter

1
Paste your JSON payload into the input editor, or choose from common invalid JSON test presets.
2
Read instant syntax validation reports indicating exact line numbers, character positions, and error explanations.
3
Click the Auto-Fix button to automatically repair common syntax issues such as trailing commas, single-quoted strings, and unquoted object keys.
4
Inspect the validated object schema, count keys, arrays, and max depth, then copy the clean JSON output.

Why use this tool?

Precise Line & Column Error Pointers

Highlights the exact line, column, and context snippet where JSON parsing fails, saving hours of manual debugging.

Smart Auto-Repair for Common Mistakes

Automatically corrects single quotes to double quotes, removes trailing commas, quotes unquoted keys, and strips comments.

Structural Metrics & Hierarchy Audit

Reports total keys, objects, arrays, byte size, and maximum nesting depth of validated documents.

Frequently asked questions

What are the most common reasons for invalid JSON?

The most frequent causes are trailing commas in arrays or objects, unquoted or single-quoted keys and string values, missing closing brackets, and inline JavaScript comments (// or /* */).

Can this validator auto-fix invalid JSON syntax?

Yes. The Auto-Fix engine fixes trailing commas, replaces single quotes with double quotes, quotes bare identifiers, and strips comments to turn invalid JSON into valid RFC 8259 compliant code.

Does my JSON data get sent to any server?

No. All validation and repair occur entirely inside your local browser sandbox. Your data remains strictly private on your computer.

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JSON Validator & Syntax Linter