Polymarket order types: GTC, GTD, FOK and FAK — and which a bot should use
Polymarket's order book takes limit orders that rest (GTC, GTD) and orders that must fill now (FOK, FAK). The choice decides whether a bot gets the trade it meant, a partial one, or a surprise.
Orders that rest: GTC and GTD
A good-till-cancelled (GTC) order sits on the book at its price until it is filled or cancelled. A good-till-date (GTD) order does the same until a time you set. Resting orders make you the maker when they are filled — the side that, per Polymarket's documentation, pays no trading fee.
Orders that fill now: FOK and FAK
A fill-or-kill (FOK) order must fill completely at once or not at all. A fill-and-kill (FAK) order fills whatever it can at once and cancels the rest. Both take liquidity, so both make you the taker and pay the taker fee where one applies.
Tick size and minimum size
Every market has a minimum price increment and a minimum order size, both published per market in Polymarket's Gamma API (orderPriceMinTickSize and orderMinSize). An order priced off the tick or below the minimum size is rejected, so a bot has to round to both before sending.
What a copy-trading bot should use
For entries, a fill-or-kill order for an exact number of shares at the best ask: either the copy happens at a price you checked, or nothing happens. An order sized in dollars can fill more shares than intended at the margin, which is why the open-source PMWallets bot sizes buys in shares. For exits, fill-and-kill at the best bid: a partial exit beats none, and the rest is retried until the position is gone.
When a killed order still filled
An exchange response can report an order as killed while part of it filled. A careful bot saves every order as pending before sending it and, when the outcome is unclear, looks the order up again until it knows — rather than assuming nothing happened and buying twice.
Questions
What is a FOK order on Polymarket?
Fill-or-kill: the order must be filled completely and immediately, or it is cancelled with nothing filled.
What is the difference between FOK and FAK on Polymarket?
FOK fills the whole order at once or nothing; FAK fills as much as it can at once and cancels the remainder.
What is the minimum order size on Polymarket?
It is set per market and published in the Gamma API as orderMinSize, alongside the tick size orderPriceMinTickSize. Check the market before sending an order.