How the RS3 Grand Exchange actually works
Why RS3 trading looks nothing like OSRS flipping, and what Varrock can honestly show you about RS3 prices.
One price a day, not a live spread
The OSRS Grand Exchange shows two live numbers for most items: an instant-buy price and an instant-sell price, moving throughout the day as real trades happen. RS3 does not work that way. Checked directly against the Grand Exchange price data (api.weirdgloop.org), RS3 items carry a single price that updates about once a day, with no separate buy and sell figure published anywhere.
RS3's exchange keeps that single price from swinging too far in one day: it moves within roughly plus or minus 5 percent a day for most items (up to roughly plus or minus 20 percent for items that only recently started trading). That is a general mechanic described in community and wiki sources, not an exact figure confirmed per item, so treat it as an approximate cap rather than a precise number for any one item.
What this means for trading RS3 items
Because there is no visible gap between a buy price and a sell price, the kind of same-day arbitrage OSRS flipping relies on does not really exist on RS3's exchange in the same form. What RS3 traders actually do instead is closer to short-term speculation: buying before a price looks likely to rise over the coming days, then selling once it has, watching the daily trend rather than an intraday spread.
This is also why Varrock's RS3 tools look different from its OSRS ones. There is no flip score, no profit-per-4-hours figure, and no buy-limit timer here, because none of those numbers can be honestly calculated from data that only updates once a day with no spread. What you do get: the current price, how it has moved day to day and over the last 7, 30 and 90 days, and a watchlist with price alerts, which matches what RS3's own trading tools focus on.
Official price data exists too, and is even coarser
Jagex also publishes its own RS3 item database (the same family of page OSRS's itemdb uses), which gives a current price, a trend arrow, and percentage changes over 30, 90 and 180 days, but no day-by-day history at all. It is useful as a sanity check, but it has even less detail than the data Varrock already uses here.