Puffin's JSON Formatter & Validator is a free browser tool for cleaning up and checking JSON. Paste raw text, drop a .json file, browse from disk, load a sample, or point at a public URL — then Process to pretty-print and validate.

Formatting uses JSON as defined by the language at json.org and the current Internet standard RFC 8259. You can label output against the older RFC 4627 or ECMA-404 for documentation clarity — parsing still follows what your browser's JSON.parse accepts.

With Fix JSON enabled, the tool attempts light recovery for common mistakes such as trailing commas and single-quoted strings before reporting an error. Nothing is uploaded to a server for formatting — processing runs in your browser (URL fetches are the exception, and may fail when the remote host blocks cross-origin requests).