PriceRadar

The context

A store selling appliances on a marketplace starts the day opening thirty tabs to see what price the competition set and copying the numbers into a spreadsheet. By eleven it's done and by two it's already stale. The worst part isn't the time: it's that the spreadsheet says who is cheaper and doesn't say the only thing that decides, which is how low you can go without the sale losing money. That number isn't on any page, because the marketplace doesn't know what the goods cost.

What the system does

• The panel appears over the listing you're looking at: nothing to export, no other tool to open
• It knows the cost, the marketplace fee and the shipping you're giving away, and with that it calculates each listing's floor
• The button says "set 371,400, leaves 17.4% margin", not "match the cheapest": that's the difference between a figure and a decision
• The cheapest seller who's out of stock is shown struck through and outside the calculation: chasing them costs margin and doesn't win a single sale
• It flags competitors that reprice automatically —twelve changes in thirty days— so you don't enter a race you lose
• It matches listings with different titles that are the same model, which is the hard part and the one that makes the comparison six wide instead of two
• Alerts are filtered by rule: six a week instead of six hundred, because an extension that over-notifies gets uninstalled