Polymarket Built-in Strategies and Custom Rules

This page covers how strategies run on regular Polymarket (platform: polymarket): how each built-in strategy enters, prices, sizes and exits here, and what is specific to custom rules: the fields, the actions, how a custom buy is priced and sized, and what the validator checks when you save. For every key and its allowed values, see All Polymarket parameters.

Built-in strategies on Polymarket

All six strategy types work on Polymarket, but the built-ins run on Polymarket's own logic, so sizes, prices and exits differ from Kalshi. Parameter meanings and bounds are on Built-in Strategies. This is how each one trades here:

Things to know before you use a built-in here:

• Entries rest at the midpoint. They are limit orders and may not fill. An entry that hasn't filled after two loops (at least 60 seconds) is cancelled. Regular Polymarket cancels by market, so any other order resting in the market is cancelled with it.
• Exits clear the market first. Before a built-in sells, it cancels whatever is resting in the market: the unfilled rest of its own entry, or an earlier exit the bid has moved away from.
• Memory starts over in each market. On series_slug or recurring, each new market starts with a fresh mean_reversion cooldown, panic_fade price history and fade count, observation_momentum history and pre_announcement_drift entry. Everything also resets when the Bot restarts.
• panic_fade holds one fade at a time. Its exit sells the YES that fade bought, never shares you held before it, and the fade stays open until those shares are sold, even when a stop below the floor rests at the bid without filling.
• observation_momentum stops at max_position and sells what it holds when the move reverses. Its backtests record no trades, because Polymarket history has no last-trade prices.
• pre_announcement_drift needs an end date. With a token-pinned market it never enters.
• rules on a built-in are ignored on Polymarket, without an error.
• Write params as plain, unquoted values. A quoted number such as cooldown: "5m", or a quoted "false", no, off, yes or on for post_only or exit_on_release, is rejected. Use unquoted numbers and unquoted true and false. See The params block.

Custom rules on Polymarket

With strategy: custom, the Bot runs your rules every loop, top to bottom. The first rule whose conditions match runs its action, and nothing else happens that loop. The full rule syntax is on Custom Rules. This section covers what is specific to Polymarket.

• Rule keys you can use here: name, when, action, size.
• At least one rule must be an exit: sell_yes, sell_no, sell_all or cancel_all. A cancel_all rule alone passes this check but never sells anything; add a sell rule if you want the Bot to close positions.
• Put exits above guards. A skip or cancel_all rule that matches first also blocks the exits below it.
• Do not use a double quote (") in a rule name or selector value, and do not end one with a backslash. The strategy saves, but the Bot fails to start.

Fields

Twelve fields work on Polymarket:

YES and NO are separate tokens with separate books. Live, the Bot never works out a NO price as 1 minus the YES price:

Empty books. A book field for an empty side has no value. Every comparison with it is false, whatever the operator, including !=, and on either side of a value_field comparison. If the NO book cannot be read on a loop, the NO fields have no value for that loop and the Bot logs a no_book error. If the YES book cannot be read, the whole loop is skipped.

unrealized_pnl can be unavailable. It is only worked out when one of your rules reads it. If a side you hold has no bid, or, on a live Bot, your holdings can't be matched to this market's recent trade history or that history can't be read, unrealized_pnl is unavailable for that loop: conditions on it are false whatever the operator, including !=, the Bot logs an unrealized_pnl error, and your other rules, exits included, still run. A P&L exit therefore can't fire until the position can be valued again, while a price exit doesn't depend on it. Keep this in mind for thin markets and for shares you moved in or out by hand. A Paper Bot values its position from its own paper fills, so there only a missing bid makes unrealized_pnl unavailable.

Actions

sell_all sells everything your wallet holds in this market, including shares you bought by hand. cancel_all cancels only orders this Bot placed: Polymarket orders carry no client id, so the Bot keeps the id of every order the exchange accepts from it, and never cancels your manual orders or another Bot's. An order from before the Bot started keeping ids is not cancelled.

How a custom buy is priced and sized

On Kalshi a custom buy takes the best ask. On Polymarket it rests at the side's midpoint, so it can sit unfilled while the market moves. Without max_entries_per_market, any resting order in the market blocks the next buy; a cancel_all rule is how you clear a stale bid.

This is the path every buy_yes and buy_no takes after its rule fires:

The position, budget, minimum-size and price steps are covered in more detail under risk.max_position, risk.max_notional, Order size and the market minimum and Price ticks and rounding.

What the validator checks

Besides field and action names, the validator checks rule behavior when you save. It rejects:

• conditions that can never match, or entries that match in every state;
• rules that earlier rules make unreachable;
• exit sets that together fire in every held state, and an exit whose only condition is on position_size and that fires whenever you hold anything (such as position_size > 0);
• entries and exits that would alternate on an unchanged market (add bounds to the entry so the exit cannot fire straight after it);
• buy sizes that max_position or max_notional can never allow.

It does not know the market minimum, so a buy with no size saves but never trades.

Warning: Paper Bots can differ from live Bots. Paper orders skip tick rounding and the price clamp, and pay no fees by default, so paper results can differ from live near the price bounds. Custom paper buys still respect the market's minimum order size. max_notional counts only resting paper buys, not filled ones, so on a Paper Bot it binds less than live and max_position is the cap that holds. max_entries_per_market counts a held position and resting buys, not completed paper trades, so after a round trip back to flat a Paper Bot can buy again where a live Bot would stop.