# 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.
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---
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:**
> 🧪 **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).
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Render(path string) string
Signatures reconstructed verbatim from vm/qfuncs — interface params keep their inline definitions.
vm/qrender output, sanitized (docs/render-security.md) and displayed in an empty-sandbox iframe — scripts, forms and popups cannot run. Links stay inert in-preview; right-click to open.