Product feed validator

This is a field checker, not a full feed review. It reads the pasted text only: links and image URLs are never fetched, so a broken URL slips through unless it is also empty or malformed. The GTIN check is the GS1 mod-10 digit over 8, 12, 13, and 14 digit codes, which catches typos but cannot tell a real assigned GTIN from an invented one that happens to checksum. The RSS side is a tag scanner over item blocks, not a full XML parser, so deeply nested or attribute-heavy markup is read loosely. Google's live feed requirements change; treat the profile as a strong baseline and the Merchant Center diagnostics as the final word.