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Use a limit order when your code needs to set a price and can wait for a match; use a market-style order when it should try to trade immediately. Neither label guarantees a fill: a limit can cross the book and execute at once, while an immediate order can fill at prices determined by available opposing liquidity. In the Polymarket client examples, limit orders use GTC, while market-style orders use FOK or FAK. The details below describe those examples and Polymarket US rulebook terms, not every Polymarket interface or a guaranteed current API schema.
What’s the difference between a limit order and a market order?
A limit order states the price at which your program is willing to trade. If it cannot match available opposing orders at that price, it may rest on the book; if the price crosses available liquidity, it can execute immediately. A market-style order instead prioritizes immediate execution, with the realized price determined by the opposing orders available when it is submitted.
| Decision | Limit order | Market-style order |
|---|---|---|
| Price control | Your code specifies an order price. | Immediate execution is prioritized; available opposing orders determine the realized price. |
| Timing | May match immediately or remain open on the book. | Attempts to execute immediately. |
| Partial fills | Can fill over time if resting; outcome also depends on order instructions and book state. | FOK requires a full immediate fill; FAK permits an immediate partial fill and cancels the remainder. |
| Key implementation choice | Check price precision, tick size, expiration, and whether the order should rest or cross. | Choose partial-fill tolerance, assess book depth, and explain price uncertainty. |
Polymarket’s FAQ says outcome-share prices range from 0.00 to 1.00 USDC and are shaped by what users are willing to buy and sell. That is product context, not a promise about the execution price of an individual order. Polymarket FAQ
How do GTC, FOK, and FAK affect execution?
GTC: allow a limit order to remain open
The Polymarket client package’s limit-order example creates an order with a token ID, price, side, and size, then posts it using GTC. In the Polymarket US rulebook, a GTC standing limit order remains in force until it is executed, cancelled, or the contract expires. Treat that rulebook description as specific to Polymarket US; do not assume it defines behavior on another interface. @polymarket/clob-client-v2 package documentation · Polymarket US Rulebook (2026.05.19)
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FOK: require a complete immediate fill
Fill-or-kill (FOK) means the order must fill in full immediately or be cancelled. Choose it when a partial position would not meet the program’s intent. A FOK instruction does not guarantee execution: the available book must be sufficient at the time of the attempt.
FAK: accept an immediate partial fill
Fill-and-kill (FAK) fills whatever is immediately available and cancels the unfilled remainder. Choose it when some immediate execution is useful but leaving the remainder resting is not. The client package presents FOK and FAK as execution types for its market-order example. Package examples
How should a developer choose an order type?
- Use a limit order when price control matters more than immediate completion, or when the order should wait for acceptable liquidity.
- Use FOK when the program needs the entire requested amount immediately or would rather not trade.
- Use FAK when an immediate partial fill is acceptable and any remainder should be cancelled rather than left open.
These are choices about intent and execution handling, not interchangeable price settings. A limit order is not necessarily passive: a price that crosses available opposing orders can execute. A market-style order does not specify a guaranteed fill price. Polymarket describes prices as reflecting users’ willingness to buy and sell, so immediate execution depends on the opposing book that is available when the order arrives. Polymarket FAQ
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The client package is useful for understanding its examples, but it is not a substitute for current official endpoint documentation. The available documentation does not establish a current raw endpoint path and payload schema, authentication headers, SDK migration requirements, market-by-market tick sizes, order defaults, or venue access restrictions. Confirm each item against the official developer documentation and the exact SDK version and venue your application targets before relying on a request shape or publishing runnable code.
- Confirm the token, side, amount or size fields, and execution instruction expected by the SDK version in use.
- Check the market’s tick size and valid price precision before constructing a limit price.
- Determine whether a limit order is intended to rest or cross available prices, and set its expiration behavior deliberately.
- For FOK or FAK, make the user-facing outcome clear: FOK can cancel without a fill; FAK can fill partially and cancel the rest.
- Inspect available opposing liquidity and avoid presenting an immediate order as a promise of a particular price.
- Confirm that the target venue supports the behavior you describe; Polymarket US rulebook language should not be generalized to other interfaces.
For implementation examples, consult the client package documentation alongside the current official documentation for the venue and SDK you are using.
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