JSON Formatter and Validator

The usual culprits are habits imported from JavaScript: a trailing comma after the last item, single quotes instead of double quotes, unquoted object keys, or NaN and Infinity as values. Copy-paste adds two more: smart quotes from Word or Slack, and invisible characters like non-breaking spaces. The validator above points at the exact line and column, and the Fix button repairs all of these in one click.

JSON5 is a relaxed superset built for config files written by humans. It allows comments, trailing commas, single quotes, unquoted keys, hex numbers and multi-line strings. Strict JSON allows none of that, and nearly every API, database and parser expects strict JSON. If a config file works locally but an API rejects it, you probably wrote JSON5. The Fix common mistakes button converts the most common JSON5 habits back to strict JSON.

Yes. Everything runs as JavaScript inside your own browser tab. Your JSON is never uploaded, sent to a server, stored or logged, and the page makes no network requests with your data. You can load the page, disconnect from the internet, and the formatter keeps working. That makes it safe for API responses containing tokens, customer records or production configuration.

An unexpected token error means the parser hit a character it did not expect at that position. Use the line and column this tool reports, then look one character earlier: the real cause is usually a missing comma between items, a missing closing quote on the previous string, or a stray trailing comma. If the token is a single quote, a letter starting a bare word, or a slash starting a comment, the Fix button will repair it automatically.

Minify anything a machine consumes. Whitespace adds 20 to 40 percent to payload size before compression and buys nothing at runtime, since parsers ignore it. Pretty-print anything a human reads: files in version control, documentation examples and debug logs. Two-space indentation is the common convention for committed files because it keeps deep structures readable without excessive line width.

Modern browsers parse multi-hundred-megabyte JSON strings, but the practical ceiling is lower because the parsed object tree takes several times more memory than the raw text. This tool formats and validates documents of any size your tab can hold, and disables only the interactive tree view above 3 MB, since rendering hundreds of thousands of DOM nodes would freeze the page.

Not to the specification: two objects with the same keys in different order are equivalent, and consumers must not rely on ordering. It matters to humans and to diffs. Sorting keys alphabetically makes committed config files deterministic, so version control shows real changes instead of reshuffles. The Sort keys A-Z toggle above applies recursive alphabetical ordering to every object in the document.