JSON Formatter & Validator
Paste messy JSON to prettify, minify or validate it in one click. Everything runs locally in your browser — nothing you paste is ever uploaded.
JSON (JavaScript Object Notation) is the lingua franca of the modern web — API responses, config files, log lines and countless data feeds are all JSON. But it's easy to end up with a single unreadable line, a stray trailing comma or a mismatched bracket. This tool lets you format (re‑indent for reading), minify (strip whitespace for shipping) and validate (confirm it parses) any JSON instantly.
It works by handing your text to the browser's own JSON.parse, then re‑serialising with JSON.stringify — a two‑space indent for formatting, or no spacing for minifying. If the input isn't valid, you get the parser's exact complaint (like an unexpected token or an unterminated string) so you can find the problem fast.
All parsing happens in your browser using native JavaScript. Your JSON is never transmitted to a server, stored, or logged. That makes this safe for API keys, internal payloads, customer records and other sensitive data — unlike many online formatters that POST your text to a backend.
JSON is strict about syntax: keys and string values must use double quotes, there are no trailing commas, and comments aren't allowed. If validation keeps failing, those are the usual culprits. Once your JSON is clean, you might need to encode it for a URL with the URL Encoder, or inspect a token that carries JSON claims with the JWT Decoder. Data like this typically travels over HTTPS — our guide on HTTP vs HTTPS explains why that encryption matters.
Because it's a static page, you can keep this open as a scratchpad while debugging an API. Refresh whenever you like; nothing is remembered and nothing leaves your machine.
Frequently asked questions
Is my JSON uploaded to a server?
No. This formatter uses your browser's built‑in JSON parser, so everything happens locally on your device. Nothing you paste is sent over the network, logged or stored — it is safe for sensitive or internal data.
What is the difference between formatting and minifying?
Formatting (prettifying) re‑indents your JSON with two spaces per level so it is easy to read. Minifying strips all optional whitespace to produce the smallest valid JSON, which is ideal for sending over a network or embedding in code.
Why does it say my JSON is invalid?
The tool reports the exact parser error, such as a trailing comma, a missing quote, single quotes instead of double quotes, or an unclosed bracket. JSON is strict: keys and strings must use double quotes and there can be no trailing commas.
Does it change my numbers or key order?
Formatting preserves your key order and values. Note that very large integers beyond JavaScript's safe range can lose precision because JSON.parse converts them to floating‑point numbers — this is a limitation of JSON itself, not this tool.
Want the theory? Read the guides → · Visit the zoo →