This page explains exactly how RuneTools produces the Grand Exchange prices, margins and profit figures you see across the site, so you can trust the numbers and reproduce them yourself.
Where prices come from
All live prices come from the official OSRS Wiki real-time prices API, which aggregates real buy and sell trades from the game. For each item we show the latest instant buy and instant sell price, the 5-minute and 1-hour average prices, and the daily traded volume, all refreshed continuously.
Instant buy vs instant sell
The instant-sell price is what you get if you sell into a standing buy offer right now; the instant-buy price is what you pay to buy from a standing sell offer right now. The gap between them is the raw margin a flipper captures.
The 2% Grand Exchange tax
Since the 2021 update, selling an item on the Grand Exchange costs a 2% tax, rounded down and capped at 5,000,000 coins per item; items that sell for under 50 coins are exempt. Every margin, ROI and profit figure on RuneTools already subtracts this tax, so the profit shown is what you actually keep.
Margin and ROI
Margin = instant-sell price minus instant-buy price minus the 2% tax. ROI expresses that margin as a percentage of the buy price, so you can compare flips of very different values on equal footing. Potential profit multiplies the margin by the item's 4-hour buy limit.
Buy limits and volume
Each item has a 4-hour Grand Exchange buy limit that caps how many you can buy per cycle, so profit per hour depends on both the margin and the limit. Daily volume shows how actively an item trades: high-volume items fill fastest and are the safest to flip.
Price history
Charts merge the Wiki's real average high/low series with our own permanently-collected daily buy/sell history, so item history keeps growing beyond the one-year window the API exposes. Older history is shown as an estimated band where exact buy/sell data is not available from any source.
Combat and skilling data
Combat stats, drop tables, equipment bonuses and skilling rates come from the Old School RuneScape Wiki. Our DPS engine is validated against the wiki's own combat calculator so damage, accuracy and max hit match the game exactly.
More detail in the about page. Try it on the live Grand Exchange, the GE tax calculator or the DPS calculator.