> For the complete documentation index, see [llms.txt](https://docs.helio.bet/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.helio.bet/orders-and-clob.md).

# Orders and the CLOB

HelioExchange is a fully funded central limit order book, or CLOB, implemented onchain. Buyers reserve collateral. Sellers reserve outcome shares they already own. This release has no leverage or borrowing.

## Price and time priority

Compatible orders match at the resting maker's price. Better prices execute first, then earlier orders at the same price. Incoming orders may receive price improvement against their limit.

UP and DOWN orders share a normalized book. A DOWN price of 0.40 corresponds to an UP price of 0.60. The contract supports three kinds of fill:

| Fill                | What happens                                                                                                                         |
| ------------------- | ------------------------------------------------------------------------------------------------------------------------------------ |
| Transfer            | A buyer receives an existing outcome from a seller.                                                                                  |
| Complementary mint  | An UP buyer and a DOWN buyer fund a new complete pair. Their share payments total one collateral unit per pair before the taker fee. |
| Complementary merge | An UP seller and a DOWN seller surrender a complete pair and receive the released collateral, with the taker's fee deducted.         |

Matching creates the same funded outcome accounting used by explicit split and merge operations.

## Order types

| Type      | Behaviour                                                                                              |
| --------- | ------------------------------------------------------------------------------------------------------ |
| GTC       | Match immediately where possible, then rest the remainder until expiry, cutoff, fill, or cancellation. |
| IOC       | Match immediately within the price and traversal limits, then release the remainder.                   |
| FOK       | Fill the entire quantity immediately or revert the transaction.                                        |
| Post-only | Rest as a maker. Revert if the order would take an eligible opposing order.                            |

All orders have an expiry no later than the round cutoff. GTC does not keep an order alive across rounds.

A partially filled maker retains its place for the remainder. Atomic cancel-and-replace creates new orders with new priority. The contract prevents same-account fills by cancelling the older maker order during normal matching.

## Units and limits

Prices range from 0.0001 to 0.9999 collateral units per share, in 0.0001 increments. In the interface's cents-style notation, that is 0.01 to 99.99, with a 0.01 tick. In the pilot these are hTEST-denominated prices, not a dollar-value claim.

Order quantities must be multiples of 0.01 share. Collateral and outcome amounts use six decimals.

Each incoming order allows at most 64 matching traversal steps. Those steps can include clearing expired entries. IOC may stop and release its remainder at the limit; other modes can revert if they need further traversal. Cancel-and-replace supports at most 32 total cancellations and new orders per call.

## Expiry, cancellation, and exposure

Expired orders cannot fill, even before someone removes them from storage. Cancellation and expiry cleanup release the remaining reservation.

Each pilot round has a 1,000 hTEST gross escrow cap. Splitting pairs and complementary minting consume that capacity. Reaching the cap can prevent an otherwise compatible incoming trade from completing. The cap does not guarantee a liquid book or an exit price.

Read [Fees and balances](/fees-and-balances.md) for charges and reservations.


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