Tools that show their rules
Every tool here publishes the complete list of checks it runs — with severities, plain-English explanations and official sources. Built for the edge cases quick scripts miss, and honest about what they cannot tell you.
Working in Claude or Cursor? Every tool here is also a local MCP server — yaktool for AI agents.
An independent project, not affiliated with any standards body or marketplace — who runs it and how the rules are checked.
Subject areas
Start here
A starting set, hand-picked for breadth — not a popularity ranking. This site has no analytics, so it does not know what is popular, and will not pretend to.
- GTIN / UPC / EAN ValidatorValidate barcodes in bulk: check digits, GS1 prefixes, Excel corruption, restricted ranges and placeholder codes.
- Google Shopping Feed ValidatorCatch Merchant Center disapprovals before you upload: required attributes, GTIN validity, identifier logic, price and enum formats.
- Excel Damage DiagnosticFind out what a spreadsheet broke in your column — and whether each value can still be repaired or is gone for good.
- Product Title CheckerCheck a title against every marketplace's length limits and style rules, with the problems highlighted on the words themselves.
- Invisible Character DetectorFind the zero-width spaces, BOM and look-alike characters hiding in your text — and see what each one is doing to your data.
- UN Number LookupSearch the Hazardous Materials Table by product name or UN number, and see every entry sharing that number with its own limits.
Why these instead of a quick script
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The rules are published, not implied
Every tool lists every check it runs — each with an identifier, a severity, a plain-English explanation and, wherever a public specification exists, a link to it. You can read what a tool does before trusting it with a file.
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The edge cases are the whole point
Check-digit arithmetic is easy to get right. A spreadsheet turning a barcode into
8.71E+12, a leading zero eaten on the way out of Excel, a restricted in-store range that will never scan in a shop — that is where a script written on the spot goes quietly wrong. Each of those is a named rule with a regression test behind it. -
Nothing is uploaded
Files are read and processed by JavaScript in your own browser. There is no server here to send a product catalogue to, which is why there is no account and no limit.