Json Validator
Free online JSON validator to check JSON syntax, find errors, and verify JSON data validity. Instantly fix and validate JSON code with ease.
What Is This Tool
JSON Validator is a free, developer-grade online utility that checks, formats, and debugs your JSON instantly - no sign-up, no server uploads, no waiting. It parses your input against the official JSON specification (RFC 8259) and, when something is wrong, tells you exactly where: the line number, column position, and a plain-English description of the problem.
Beyond validation, the tool doubles as a formatter and minifier. One click expands compressed JSON into readable, indented output for review; another strips it back down to a compact single line for production use. All processing happens entirely inside your browser, so API keys, database configs, and any other sensitive data you paste in never leave your machine.
Whether you're debugging a failing API response at midnight, cleaning up a config file before a deploy, or just learning how JSON works, this tool gives you a fast, reliable answer with no friction.
How to Use
- Paste your JSON into the Input panel on the left, or click Load Sample to see a working example. The character and line count update automatically as you type.
- Validate - click Validate to check your JSON for syntax errors. If it's valid, you'll see a green confirmation and a formatted copy of your data in the output panel. If it's invalid, the error message tells you the exact line and column to fix.
- Format - click Format to expand minified or messy JSON into clean, 2-space-indented output that's easy to read and review.
- Minify - click Minify to strip all whitespace and produce a compact single-line version optimized for API payloads and storage.
- Copy the output - click Copy Output, or simply click anywhere inside the output box to copy the result to your clipboard immediately.
- Clear everything - click Clear to reset both panels and start fresh.
Key Features
- Precise error location: When validation fails, you get the exact line number and column position - not just "invalid JSON." This makes it fast to locate and fix issues even in large payloads.
- Format and minify: Switch between human-readable indented output and compact single-line format with one click, without re-validating manually.
- Live character and line stats: Both input and output panels show real-time character and line counts, so you always know the size of what you're working with.
- RFC 8259 compliance: The parser enforces the full JSON standard - catching trailing commas, single quotes, unquoted keys, comments, and other common mistakes that strict parsers reject.
- 100% client-side: Everything runs in your browser. No data is sent to any server, ever. You can disconnect from the internet and the tool still works.
- Click-to-copy output: Click anywhere in the output box to copy its contents instantly - no need to select all manually.
- Responsive layout: Works cleanly on desktop and mobile without horizontal scrolling or layout breakage.
Common Use Cases
- Debugging API responses: Paste a raw API response to instantly check whether the JSON is well-formed and see its structure formatted for inspection.
- Validating config files: Check
package.json,tsconfig.json,.eslintrc, or any other JSON config before committing or deploying. - Minifying for production: Convert formatted JSON to a compact payload to reduce response size and bandwidth.
- Formatting for review: Expand compressed or machine-generated JSON into readable output for code review, documentation, or debugging.
- Catching copy-paste errors: Spot invisible smart quotes, trailing commas, or encoding issues that come in when copying from Slack, email, or rich-text editors.
- Learning JSON syntax: Use the sample data and error messages to understand what valid JSON looks like and what breaks the parser.
Frequently Asked Questions
What errors does this tool detect?
The parser catches all standard JSON syntax errors: trailing commas, single quotes instead of double quotes, unquoted object keys, missing or mismatched brackets and braces, unescaped special characters in strings, and inline comments (// or /* */), which are not valid in JSON. The error message includes the line and column where the problem was found.
My JSON looks correct but the validator says it's invalid - why?
The most common cause is "smart quotes" - curly quotation marks (" ") that word processors and some chat apps substitute for straight double quotes ("). Other common culprits: a trailing comma after the last item in an object or array, or a hidden whitespace character from copying out of a PDF. The error location in the output will point you to the right spot.
What's the difference between Format and Minify?
Format (beautify) adds consistent indentation and line breaks, making JSON easy to read and review. Minify does the opposite - it removes all whitespace to produce the smallest possible representation, which is useful for API payloads, localStorage, or anywhere payload size matters.
Is it safe to paste sensitive data like API keys or database configs?
Yes. The tool runs entirely in your browser using JavaScript. Nothing you paste is sent to a server or stored anywhere. You can verify this by opening your browser's network tab - you'll see zero outbound requests when you validate or format. Turning off your internet connection won't affect the tool at all.
Is there a size limit?
There's no hard limit imposed by the tool. In practice, the browser handles JSON files up to several megabytes without issue. Very large files (50 MB+) may slow down depending on your device's available memory. For extremely large datasets, a command-line tool like jq may be more practical.
Advanced Tips
- Check the line before the error line: JSON parsers often report an error on the line after the actual problem. If the validator flags line 12, check whether line 11 is missing a comma or closing quote.
- JSON requires double quotes: Single quotes (
') are not valid in JSON, even though they work in JavaScript. All keys and string values must use double quotes ("). - No comments allowed: Standard JSON does not support
//or/* */comments. Strip them before validating. If you need comments in a config file, consider JSON5 or JSONC formats instead. - No trailing commas: A comma after the last item in an object (
{"a":1,}) or array ([1,2,]) is a syntax error in JSON, even though modern JavaScript allows it. - Watch out for number precision: Very large integers (beyond 2^53) may lose precision when parsed in JavaScript. If you're working with large IDs, keep them as strings.