JSONLint Alternative — JSON Validator and Formatter
Validate and format JSON entirely in your browser — no data sent to any server. Instant syntax errors with line numbers, beautify, and minify.
Why Use This JSON Validator
If you've used JSONLint, you already know what you need: paste JSON, see whether it's valid, and get clear error messages. This tool does exactly that — and because all processing runs locally in your browser, your JSON never leaves your device. That matters when you're working with API keys, auth tokens, or production config files.
- Instant validation: Syntax errors are highlighted with exact line and column numbers
- Beautify / format: Reindents and pretty-prints JSON with configurable indent size
- Minify: Strips all whitespace to reduce payload size for production use
- Clear error messages: Explains what's wrong — trailing comma, unquoted key, mismatched bracket
- No account needed: Open the page and start pasting — no sign-up, no rate limits
Choose the Right Variant
- This page: Validate JSON syntax and reformat — the core workflow most developers need
- JSON Formatter: Full formatter with tree view, path copying, and collapsible nodes
- JSON Validator Online: Strict RFC 8259 validation with detailed diagnostics
- JSON Minifier: Focused minification for shrinking API payloads
Key Features
- RFC 8259 compliance: Catches errors that lenient parsers silently accept — trailing commas, single-quoted strings, unquoted keys,
NaN/Infinityvalues - Line-level error location: Reports the exact line and character offset so you jump straight to the problem
- Large file support: Handles JSON files up to tens of MB without uploading anything
- Configurable formatting: Choose 2-space, 4-space, or tab indentation when beautifying
- Offline capable: Once the page loads, validation works without a network connection
- One-click copy: Copy formatted or minified output to clipboard in a single click
Privacy and Data Handling
All processing runs in your browser using the built-in JavaScript JSON.parse engine. No data is sent to any server. This is especially important when validating config files that contain database credentials, API secrets, or tokens — none of that ever leaves your machine.
Frequently Asked Questions
Is this as accurate as JSONLint?
Yes. Both tools validate against the same JSON specification (RFC 8259). The underlying parser is your browser's native JSON.parse, the same engine used by Node.js and virtually every JavaScript runtime. It catches all standard JSON syntax errors: trailing commas, unquoted keys, single-quoted strings, mismatched brackets, invalid escape sequences, and values like undefined or NaN that are valid in JavaScript but not in JSON. The key difference is that this validator runs entirely client-side, so your data stays on your device.
Does it work offline?
Yes. After the page loads once, the validator runs entirely in your browser with no network calls required. This makes it practical for validating JSON while on a train, in a meeting with spotty Wi-Fi, or in an air-gapped development environment. The page itself is lightweight, so the initial load is fast even on slow connections.
Can it handle large JSON files?
Modern browsers can parse JSON files of 10–50 MB comfortably in under a second, limited only by your device's available memory. For very large files (over 100 MB), performance depends on the browser and device. If you're regularly validating files that large, consider using the command-line tools jq . file.json or python -m json.tool file.json which are more memory-efficient for bulk processing.