Validate JSON or YAML and get a clear error message with the line that failed. Valid JSON is pretty-printed so you can read it immediately.
JSON is parsed exactly, so its validation is authoritative. The YAML check is a structural lint — it catches indentation problems, bad list markers and malformed keys, but it is not a full YAML parser.
Yes. For JSON the reported position from the parser is included, and for YAML the offending line number is listed.
No. Validation runs entirely in your browser.