Validate

Find syntax errors in JSON strings with precise line numbers

Parse and validate JSON strings to expose syntax errors at exact line and column positions.

🛡️ Your rows never leave your browser.

Why Onfyt: Pinpoints the exact character position of JSON errors—not just 'invalid JSON'—so you fix the right spot on the first attempt.

Interactive Sample Data

raw_json	status
{"id":1,"name":"Grace","active":true}	active
{"id":2,"name":"Peter","active":false,}	active

How this tool works

JSON is strict by design—a single trailing comma, an unmatched bracket, or a bare control character will make any conformant parser throw an exception. Production systems that consume API webhooks or message-queue payloads must validate incoming JSON before passing it to downstream deserialization layers. DataFix's validator reports the line number, column offset, and character that caused the parse failure. It also detects common near-misses such as trailing commas after the final element (valid in JavaScript, invalid in JSON), unescaped newlines inside string values, and single-quoted keys which are JavaScript-syntax but not valid JSON. Syntactically invalid JSON breaks API gateways, microservice communication, and database migrations. Common JSON errors include trailing commas in arrays, single quotes wrapping keys instead of double quotes, missing colons between keys and values, unescaped control characters within strings, and mismatched enclosing brackets. DataFix executes deep structural syntax validation directly inside your browser. When a syntax error occurs, the validator pinpoints the exact line number, column offset, and token context, displaying an intuitive visual highlight and actionable remediation advice so you can fix malformed payloads immediately.

Things that usually go wrong

Trailing commas after the last element are the most common JSON syntax error.
Single-quoted strings ('hello') are JavaScript syntax, not JSON. All strings must use double quotes.

Edge cases we tested

🧪 Trailing comma after last object key

Reported with exact line; auto-repair mode can strip it.

🧪 JSON Lines format (one object per line)

Each line validated independently; per-line errors listed separately.

🧪 Escaped Unicode surrogate pairs

Valid surrogate pairs (\uD800\uDC00) pass; isolated surrogates flagged.

🧪 Deeply nested objects (20+ levels)

Nesting depth reported; validation still completes without stack overflow.

Frequently Asked Questions

What is the difference between Validate JSON and Format JSON?

Validate only checks syntax. Format also pretty-prints the JSON. If validation fails, formatting also fails.

Are large JSON files supported?

Files up to 10 MB are validated in-browser without any server upload.

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