Order Book#

Seesaw's on-chain matching engine pairs buyers and sellers of YES shares.

Order Book Architecture#

Each side of the book holds up to 63 resting orders. Prices are in basis points of one stablecoin unit: 10,000 bps = 1.00 USDT, and valid trading prices live in [1, 9999].

Single Book Design#

Seesaw maintains one order book per market for YES shares only. All NO orders are converted by price complement:

Matching is complementary only: BuyYes↔SellYes and SellNo↔BuyNo pairs meet on the canonical book. One book concentrates liquidity, eliminates YES/NO arbitrage, and keeps YES @ 0.60 complementary to NO @ 0.40 by construction.

Escrow-Based: Fills Move Real Assets#

Every resting order is fully backed before it can rest:

• A bid (buy) locks its full collateral (shares × price) in the market vault at placement.
• An ask (sell) escrows the actual SPL share tokens in the market's YES or NO escrow PDA at placement.

A fill is therefore an escrow transfer, never a mint: shares move from the maker's escrow to the taker, and stablecoin moves through the vault to the seller. New shares come into existence only through MintShares (pair-minting YES+NO 1:1 against stablecoin) and WithdrawShares (materializing internal-ledger shares); shares are destroyed only by Redeem. See Flow of Funds.

The *WithFreeFunds order variants (0x0D–0x0F) place the same orders against your internal trader-ledger balances — no wallet token transfer per order, same matching rules.

Order Types#

IOC protections#

IOC orders may additionally set:

• worst_acceptable_price_bps — a hard slippage bound; the program will not fill past it.
• min_fill_quantity — cancel rather than accept a fill below this size.
• match_limit — caps how many resting orders one instruction visits (default 63, i.e. effectively unlimited relative to a full side).

Market-style orders: use IOC#

To "buy at market," submit an IOC order with a generous limit and a worst_acceptable_price_bps you're comfortable with. Don't submit a Limit order at an extreme price (e.g. 9900) — Limit and PostOnly orders must pass the maker price band (±10% around the midpoint on a two-sided book), so an extreme resting price is rejected. IOC orders are exempt from the band because they never rest.

Per-order TTL#

Resting orders may carry max_age_seconds > 0. Once expired, the order is ignored by matching and becomes reclaimable by anyone via ReclaimExpiredOrder (0x19) — the refund goes to the maker, and the caller may take a bounty of 10 bps of the refund (capped at 0.1 stablecoin). The TTL may not outlive the market (expiry ≤ t_end).

Price-Time Priority#

Orders match on price first, then arrival order (FIFO):

Same-price ties break by the order's monotonic order_id (allocation order), not by timestamp.

Matching Algorithm#

Fills execute at the maker's resting price — price improvement goes to the taker:

incoming = Sell 100 YES @ 0.55 (Limit)

while incoming.quantity > 0:
    best_bid = book.best_bid()
    if best_bid is None or best_bid.price < incoming.price:
        break                          # nothing crosses

    fill_qty = min(incoming.quantity, best_bid.quantity)
    execute_fill(price = best_bid.price, quantity = fill_qty)
    # maker's escrowed/locked assets move; taker pays the fee

    incoming.quantity -= fill_qty

if incoming.quantity > 0:
    book.rest_ask(incoming)            # Limit only; IOC cancels instead

Tick Size#

Prices must align to the market's tick:

Tick Rounding Rules#

• Bids round DOWN to the nearest tick
• Asks round UP to the nearest tick

Both directions are conservative for the order's owner and the book:

Submitted: Buy @ 0.5567,  tick 0.01  →  Buy @ 0.55  (down)
Submitted: Sell @ 0.5567, tick 0.01  →  Sell @ 0.56 (up)

An ask that would round to ≥ 10,000 bps is rejected (there is no valid price at or above 1.00).

Resting-Order Quality Gates#

Two placement-time gates keep the book clean:

• Maker price band — Limit/PostOnly orders must price within ±10% of the midpoint on a two-sided book (static 1%–99% band otherwise). IOC is exempt.
• Minimum resting notional — a remainder too small to be worth matching is rejected rather than allowed to rest (UpdateMinRestingNotional, 0x2A).

No Crossed Book Invariant#

The order book cannot have best bid ≥ best ask:

If a new order would cross, it immediately executes against resting orders until uncrossed or fully filled.

No Naked Shorts#

You can only sell shares you own (in your wallet or your internal ledger balance):

Alice owns: 50 YES shares

✓ Sell 50 YES @ 0.60  (valid — 50 shares escrowed)
✗ Sell 100 YES @ 0.60 (rejected — insufficient shares)

To bet against YES without owning it:

1. Buy NO shares, OR
2. Mint a YES+NO pair (MintShares) and sell the YES

Order Lifecycle#

Reading the Order Book#

Depth Chart#

Price    Bid Size    Ask Size    Cumulative
─────────────────────────────────────────────
0.65                 200         650
0.60                 300         450
0.58                 150         150
────────── spread ──────────
0.55     100                     100
0.54     250                     350
0.52     500                     850

Key Metrics#

For how the app turns book depth into a fill preview (average price, slippage, price impact), see Slippage & Fill Estimation.

Order Book Events#

Every book mutation is recorded on-chain through the program's binary event recorder (the internal LOG self-CPI), so indexers and UIs can reconstruct the book deterministically. The order-flow event kinds:

How-to guides#

For task-oriented guidance on using this order book:

• Market makers (quoting both sides, PostOnly, spread capture, inventory management): Market Making
• Takers (fill preview, IOC slippage protection, splitting large orders, fee curve): Placing Orders