Checks supplied GTIN-8, GTIN-12, GTIN-13 and GTIN-14 text for length, digits and checksum. A valid checksum does not establish ownership, assignment or a genuine product. No registry lookup. Uses explicitly supplied structured inputs. Server computations are transient; the standalone website computes locally in your browser. Review the output before exporting it. No persistent account records, external source retrieval, sending, transactions or paid model calls. CSV/JSON review and export are available on the standalone website. MCP requests are capped at 128 KiB and computed responses at 256 KiB; individual field and record limits also apply.