The book and the curve
Runner is a central limit order book that runs fully on chain. The book is an account of the Runner program on Solana, and the program does the matching. Every trade is a buyer and a seller meeting at a price on that book. There is no pool pricing against a formula and no house on the other side.
Ladders
Each market's book holds its strikes. Each strike has four ladders, for call bids, call asks, put bids and put asks. A ladder fills in price-time priority.
A buyer who crosses the best ask takes. The order walks the ask ladder from the best price until it is filled or reaches its limit. See Fees for what takers and makers pay.
A take never trades with you. It passes over your own resting orders and your own curve paint and fills the makers behind them, so the price the desk quotes you is what the other makers on the ladder offer. A limit order whose unfilled rest would sit on the book crossing one of your own orders or quotes is refused: cancel yours first, or send it immediate-or-cancel.
Orders and curves
Makers put liquidity on a ladder in two ways, and both rank together on it.
Discrete orders. A limit order at a premium for a fixed quantity, post-only, limit or immediate-or-cancel. A resting sell reserves its full deliverable while it rests, so the order is backed whether or not it fills.
The quote curve. A maker publishes a premium mid and up to eight regions around it for each strike and side they quote. Each region is a size at mid + offset. The book turns the curve into orders at the moment someone trades against it. The Write page paints asks this way (see Write options).
Backing at fill
A painted region locks no collateral of its own. The maker sets aside a paint reserve on each token — part of its account that withdrawals and orders cannot touch — and every region it paints on that token is backed by that one reserve at the moment of each fill. A paint is accepted only while the reserve covers its largest single region in full; fills draw the reserve down, and paint beyond what is left is shown with its backing and never executes until the maker tops the reserve up.
So one maker can quote a full strike grid from one reserve and move every quote with one instruction.
A quote is the maker's to keep only while the maker keeps it. One the maker has not touched for the market's stale window (a day unless the market sets its own) — any repaint or mid move counts, even one that changes nothing — or that its reserve can no longer fill, anyone may take off the book.
Reduce-only
Orders and curve regions can be marked reduce-only. They only close an existing position and never open a new one.
Close-only and the protocol pause
The protocol can be paused, everywhere at once, one family of instructions at a time: listing new markets, strikes and curves; opening new positions; trading; deposits; withdrawals; and settlement (exercise and the writer's claim). A paused family is refused for everyone until the pause is lifted. Cancelling an order, closing an empty slot and removing paint are never paused, so anyone can always unwind. The desk says what is paused and switches off what would be refused.
While opening is paused, every market is close-only: positions can still be closed, sold and exercised, and only reduce-only orders and paint are accepted. There is no switch for one market alone.