Paste JSON and get it pretty-printed with proper indentation, or minified to a single line. Syntax errors are caught immediately, so it doubles as a JSON validator.
No. Formatting and validation run entirely in your browser — the data never leaves your machine.
Anything that makes JSON invalid: missing commas or quotes, trailing commas, unclosed brackets, bad escapes.
Yes, within your browser's memory — documents of several megabytes format without problems.
Minification strips whitespace to shrink payloads sent over the network or stored in databases.