# Luhn Checksum > ⚠️ **Experimental — generated with no human supervision** by the daily MCP pipeline to exercise gno tooling. Not audited. See [r/moul/x/daily](https://github.com/moul/gno-contracts/blob/main/r/moul/x/daily/README.md). --- Put a number in the path and the realm tells you whether its Luhn check digit is right — and if not, what it should have been. Demo of the [`p/moul/x/daily/luhn`](https://github.com/moul/gno-contracts/tree/main/p/moul/x/daily/luhn/v0) library — validation, the check digit and the separator handling all come from the package; this realm holds no checksum logic of its own. Read-only and stateless, so `Render` is fully deterministic. ``` /r/moul/x/daily/luhndemo/v0 → usage + worked samples /r/moul/x/daily/luhndemo/v0:79927398713 → valid /r/moul/x/daily/luhndemo/v0:79927398710 → invalid, suggests check digit 3 /r/moul/x/daily/luhndemo/v0:4539-1488-0343-6467 → separators are ignored ``` The samples on the root page are picked to show the two error classes Luhn actually catches: a wrong digit, and two adjacent digits swapped. Built for gno 0.9. --- Part of **[moul/gno-contracts](https://github.com/moul/gno-contracts)** — moul's versioned gno.land contracts. See the repository for the full catalog, build/test tooling, and usage. **Dependency graph:** ![gno.land/r/moul/x/daily/luhndemo/v0 dependency graph](https://raw.githubusercontent.com/moul/gno-contracts/main/_assets/gno.land/r/moul/x/daily/luhndemo/v0/deps.png) > 🧪 **Highly experimental — potentially vibe-coded.** Not audited; may break, change, or be removed at any time. Do not use with anything of value. Full disclaimer: [DISCLAIMER](https://github.com/moul/gno-contracts/blob/main/DISCLAIMER.md).