Fractional fee on a maker fill; negative for a rebate.
Fractional fee on a taker fill (a quote submitted already crossing the spread).
Fill rule for a trade at your price. "touch" fills a participation partial; "breach" fills only on a trade through.
Fraction of an at-price trade's size captured (front-of-queue at 1.0).
Price step a marketable order walks for the size beyond the displayed quote.
Inventory floor; sell fills are capped so the position never falls below it.
Inventory ceiling; buy fills are capped so the position never exceeds it.
Contract multiplier applied to mark-to-market PnL, fill slippage, and proportional fees.
Fixed fee (or rebate when negative) charged per contract on maker fills.
Fixed fee (or rebate when negative) charged per contract on taker fills.
https://screamer.readthedocs.io/en/latest/ for the Python reference and full details.
Backtest a two-sided market maker against top-of-book quotes with a trade tape driving the fills, into a costed equity curve.