How to build a simple inventory that never goes stale
A simple inventory is a number next to every product that runs out, and it only stays accurate when it's deducted automatically with each paid sale — not when you remember to write it down at night.
Don Braulio runs a feed store in Salamanca. On Thursday a customer pulled up with his truck out front for two sacks of rabbit feed. “Yeah, I’ve got some, let me grab them.” The notebook said five. The shelf said zero.
It’s not that Don Braulio doesn’t keep track. He does: he counts the sacks every Monday and writes down what sells “later, when things calm down.” But Tuesday the seed supplier showed up, Wednesday his daughter had a school festival, and two days’ worth of “later” never arrived. The notebook wasn’t wrong by much. It was wrong by three days — and that was enough to let down the one customer of the day who was in a hurry.
If you keep a simple inventory in a notebook, on a whiteboard, or in an Excel sheet, you already know this scene. And you’ve probably already tried to fix it with more discipline. The good news is discipline was never the problem.
What is a simple inventory?
A simple inventory is a number next to every product that runs out — how many you have left today — placed somewhere the sale itself can subtract from. That last part is what separates it from a well-intentioned list.
It’s not your catalog. The catalog answers the customer’s question, “do you have it?”; the inventory answers yours: “how much is left, and what do I order this week?” You can have a catalog without inventory — you show what you carry, without counting pieces — and for a lot of businesses that’s enough. Inventory starts to matter the day you said “yeah, I’ve got it” and you didn’t.
Why does your inventory always go stale?
Because writing it down is a second job, separate from selling, and the second job always loses. The sale happens at eleven in the morning, with the store full and the customer waiting for change; the note-taking gets promised to the evening, and the evening has closing up, dinner, and exhaustion.
That’s why switching tools doesn’t save you. The notebook, the whiteboard, and the spreadsheet all fail the same way, because they share the same factory defect: between the sale and the number, there’s a person who has to remember. Every unrecorded sale is a small debt, and small debts don’t get paid off — they pile up. By Thursday, the number isn’t information anymore: it’s a story about how the store looked on Monday.
The right question isn’t “how do I remember to write it down?” It’s “how do I make the sale write it down by itself?”
How does inventory deduct itself automatically?
When an order comes in through your own page and gets paid, the number drops without anyone touching it. A working inventory has exactly two writers: you, when you restock, and the sale, when it gets paid. No one else — not your memory, not the evening, not “later.”
On a page built with Proyecta, it works like this: if the customer pays by card, the number drops right then. If the order is cash-on-delivery or bank transfer, it stays pending payment, and the number drops when you log that payment in your console — a button you tap while collecting, not a note you jot down at night. The difference sounds small, and it’s the whole point: tapping “Log payment” is part of collecting, and you never forget to collect. Writing it in the notebook was a separate job, and separate jobs fall through the cracks.
You only touch the number when the supplier shows up: you go into the console and update how many sacks there are. From then on, every paid order takes it down on its own.
Which products need a number?
Only the ones that run out. A product with no number sells normally, as if you had plenty, and it never shows as sold out — so you’re never forced to count the entire store just to get started.
Of the forty-something products Don Braulio carries, putting a number on eight is enough: the feeds that run out every week. Wire, feeders, and buckets don’t need a counter — he’s never once said “I’m out” of those.
Start there. Eight numbers that tell the truth are worth more than the whole store counted once; everything else can go without a counter for as long as you like.
What happens when a product hits zero?
Your page marks it “Sold out” and turns off the order button, on its own. No one can ask you for a sack that no longer exists, and Thursday’s “yeah, I’ve got it” disappears because the page told the truth before you had to.
And if you work on backorder, there’s a way to handle that too: you can mark a product as pre-order, and it keeps selling even at zero — useful for whatever you order from the supplier every week. The difference is that now it’s a decision you made per product, not an accident you discover with the customer standing in front of you.
What’s still your job?
Two things: the counter, and ordering from the supplier. A sale that didn’t go through your page doesn’t move any number — if someone walks in, pays cash, and walks out with a sack, you’re the one who subtracts it in the console, because the page never knew about it. If most of your business is in-person, the number still works for you, just as a checkpoint: you adjust it once a day, and the page’s orders keep it honest in between.
And no one’s going to warn you that something’s running low. The number is there for you to see when you open your console; there’s no “time to order from your supplier” message — that call is still yours to make. Inventory takes writing it down off your plate. It doesn’t take the thinking off your plate.
Start without going to the storeroom
Run a test before you set anything up. Pick the product that runs out most often and say how many you have left, without going to look. Then go count them. The gap between your two numbers is the real state of your inventory today — and it’s the same gap a customer with a truck out front is about to discover for you.
If you got it right, you already have a system that works; don’t touch it. If it went like it did for Don Braulio, describe it at proyecta.dev: “a page for my feed store in Salamanca, with my sacks and their prices, cash-on-delivery orders, and rabbit feed that marks itself sold out the moment it runs out.” It comes out published, with its own link and a console where the number drops with every paid order. The only two things still written by hand are the ones that were always yours: restocking, and collecting.