Series: AI × Supply Chain build breakdown
Stack: Shopify · Material Manager · Google Sheets
The problem
You want a running stock number you can trust on any given day, not just the day after a count. Shopify’s own inventory drifts as orders, returns and adjustments pile up, and a real warehouse system is overkill and over-budget for a small CPG brand.
What I built
A cheap inventory app (Material Manager) as the perpetual layer over Shopify, feeding the same spreadsheet brain everything else reads. On-hand stays current between counts, so the month-end count becomes a quick reconcile instead of a from-scratch slog.
Where it bit me
The app shows a few columns that all look like “stock on hand”. Only one of them actually is. The others are sold-count and variant views, and grab the wrong one and everything downstream is quietly off. Each SKU also carries a few variant rows you must never add together.
The real lesson: perpetual inventory isn’t a tool you turn on. It’s a discipline about knowing which number is the truth and guarding it. The tool’s the easy part.
Leverage rating: 3 / 10
Unglamorous. But it’s the floor the supply agent and the month-end count both stand on, and nothing built on top is trustworthy without it.
Related: this is the foundation the Shopify Ops Starter is built to own. Email me for the setup.