One item per line: the item name, an optional quantity such as 2x, the price, then who shares it (names separated by commas, "all", or nothing for everyone). An optional "people:" line fixes the participant list and order; "adjust Ada +15000" makes Ada pay that much more while the others pay proportionally less. Tax, service and discount (percentages or amounts) are allocated in proportion to each person's subtotal; optional rounding shows its difference against the bill; naming the payer prints who pays whom. The summary is plain text ready to paste into a chat. Everything runs locally.
0 keeps exact shares.