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Numo matches orders off chain and settles every fill on chain. The order book lives in markets-service. Each fill is submitted to Matching.verifyAndMatch on Base, which checks both signatures and moves the assets.

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How a match happens

  1. You submit a signed order to POST /v1/orders. It rests on the book.
  2. The matcher polls the book several times a second. On each pass it takes the best crossed pair in each market, in price-time priority.
  3. The fill size is the smaller of the two remaining amounts. The fill price is the maker’s limit price.
  4. The execution service submits the fill on chain. Your order’s filled amount updates once the transaction settles.
A market handles one fill at a time. A large order fills against resting orders one by one.

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Maker and taker

The order created later is the taker on each fill. The earlier one is the maker. If both were created at the same instant, the one with the higher order_id is the taker. See Fees for what this means for what you pay.

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When a fill would revert

The matcher simulates each fill before it is sent. If the chain would refuse it, both orders stay on the book.
  • A refusal that depends on balances (for example, an account short of margin) is retried with backoff. Nothing is cancelled.
  • A refusal that cannot change while both orders stay as they are skips that pair. Each order can still fill against other orders. An order refused this way against three different subaccounts is cancelled with cancel_reason: "repeated_permanent_revert".
  • An order that can never settle as signed is cancelled with cancel_reason: "unmatchable_signed_order".

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Futures

The matcher skips a futures series while it is closed on chain: before it opens, after last_trade_time, or while its manager is paused. Before each futures fill it also checks: