The validator goes beyond a basic parse error and identifies the root cause for all of these patterns automatically: missing commas between values or key-value pairs; trailing commas before a closing } or ]; Python literals (True, False, None — which must be true, false, null in JSON); JavaScript-only values (undefined, NaN, Infinity — none are valid JSON); single-quoted keys or values (JSON requires double quotes); unquoted or numeric object keys; JS-style line comments (//) and block comments (/* … */); an = sign used instead of : between key and value; unterminated strings (missing closing quote); unclosed or mismatched brackets — the checker is string-aware so characters inside values are not miscounted; and typographic 'curly' quote characters that look like standard quotes but are rejected by JSON parsers. A UTF-8 byte-order mark (BOM), common in Windows-saved files, is silently stripped before parsing so it never causes a spurious error.