One number,
and it is the true one.

The thing people actually buy is a medium in bone, so that is what gets counted. Each combination carries its own number, its own low line and its own status, and a paid order takes it down by itself.

• Amber when it reaches the line you set, red when it is gone.
• A sale that would take you below zero is refused rather than oversold.
• Stock comes down exactly once, even if a payment notification arrives twice.
• Some things you never want to count. Turn tracking off and they simply sell.

A shop, a market van and a storeroom, each with its own count and one total that stays true. An online order draws from the place you nominated; a till sale draws from where the till is standing. Move stock between them and the move itself is written down.

• Every movement is recorded and never edited: sales, restocks, returns, transfers, corrections.
• A sale that would oversell is refused and tells you where the stock actually is.
• A return puts the units back on the shelf the order came off, not just anywhere.
• Included in the store. Some tools charge per location for this. This one does not.

It is opt-in by design. Until you add a second place, none of this exists for your shop and nothing about it runs.

A deli sells coffee at a price per kilo and somebody walks out with 250 grams. Until you can say that properly, that sale can only be told as a fib. Price a product per kilo, per metre or per litre and the quantity is allowed to be a real amount.

• A decimal quantity is only ever allowed on a product priced that way.
• An ordinary countable product refuses half of itself, in plain words, instead of rounding.
• The line is worked out once, so the totals cannot drift by a cent.

One thing on the shelf that is really three things in the stockroom. A bundle holds no stock of its own, because a second number is a second thing to be wrong. How many kits you can make is simply the smallest answer its parts give.

• For each tracked part: how many you have, divided by how many the kit needs, rounded down.
• The smallest of those answers is how many kits are available. Nothing else to maintain.
• A part you do not track is ignored, so it can never be the thing that runs out.
• Selling a kit takes its parts down, so the shelf and the website agree.

Your own part number is one thing; the manufacturer's barcode printed on the box is another. A product or a size can carry both, and keeping them apart is what stops a shopping feed being rejected and a scanner finding the wrong thing.

• Scanning looks for the barcode first, then falls back to your SKU.
• A shop that only ever filled in a SKU keeps working exactly as it did.
• Google is sent the manufacturer barcode and your part number in their own fields.
• A Shopify export carries both columns, and both come across on import.

Size, colour, collection, price, in stock. Built from your own catalogue rather than typed into a form by you, because the answer is already sitting in your products. Then you adjust: hide an axis, rename it in your own words, pin your favourites first.

• It works on your search results and on a ready-made all-products page you can switch on.
• It also works on the shop page you designed yourself, without changing a byte of it.
• Price ranges come from your real prices, not from round numbers somebody guessed.
• Only the things you changed are remembered. The rest keeps following your catalogue.

You type a real price per currency. Yetty never invents an exchange rate, because a rate nobody maintains daily is a lie that charges real money. And you can give a group of buyers their own prices, with a from-this-many rule if you want one.

• A basket stays in one currency from start to finish, and reports never add two into one.
• A product with no price in a currency is simply not sold in it, and the cart says so.
• A trade group sees its prices only once signed in. Nobody else ever does.
• A price you left blank means that group pays your normal one. No trap doors.