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Ascend uses a Central Limit Order Book (CLOB) for price discovery and trade execution. Traders place bids and offers at specific probability prices, and the matching engine pairs compatible orders. This is the same orderbook model used by major exchanges. No AMM, no bonding curves, no protocol-owned liquidity. Just traders trading with each other.

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How the Orderbook Works

The orderbook is a live list of open orders, split into two sides:
  • Bids (LONG): Buyers posting “I will pay up to this price.” The highest bid is the best one. It is closest to getting filled.
  • Asks (SHORT): Sellers posting “I will accept this price or higher.” The lowest ask is the best one. It is closest to getting filled.
The gap between the best bid and the best ask is called the spread. That is the cost of trading immediately. Example: BTC $100k market:
Bids (LONG)PriceAsks (SHORT)
65%500 USDC
64%1,200 USDC
800 USDC63%
2,000 USDC62%
1,500 USDC61%
Reading this: the best bid is 63% (the highest price a buyer posted). The best ask is 64% (the lowest price a seller posted). The spread is 1%, the gap between them.
  • Want to go LONG right now? You match the best ask and pay 64%.
  • Want to go SHORT right now? You match the best bid and receive 63%.
Want a better price? Place a limit order and wait for someone to match you.

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Order Types

Ascend supports standard order types:
You specify a price and size. Your order rests on the book until:
  • It gets matched with an incoming order
  • You cancel it
  • It expires (if you set a time limit)
Example: You place a limit order to LONG 500 USDC at 62%. Your order sits on the bid side. If someone comes in willing to SHORT at 62% or lower, you get filled.Use when: You want a specific price and are willing to wait.

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Matching Logic

The matching engine follows price-time priority:
  1. Best price first: Orders at better prices get filled before orders at worse prices
  2. Earlier orders first: At the same price, older orders have priority
This ensures fair execution with no preferential treatment. Example: Three traders place LONG limit orders at 62%:
TraderTimeSize
Alice10:00:01500 USDC
Bob10:00:05300 USDC
Carol10:00:10400 USDC
A new SHORT market order comes in for 600 USDC. Fills:
  • Alice gets filled: 500 USDC (she was first)
  • Bob gets filled: 100 USDC (partial fill, he was second)
  • Carol gets nothing yet (Bob’s remaining 200 USDC fills before her)
Bob’s remaining 200 USDC order stays on the book.

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Partial Fills

Orders can be partially filled when available liquidity is insufficient. Example: You place a market order to LONG 1,000 USDC. The orderbook looks like:
PriceAsk Size
64%400 USDC
65%300 USDC
66%500 USDC
Your order fills across multiple price levels:
  • 400 USDC at 64%
  • 300 USDC at 65%
  • 300 USDC at 66%
Total: 1,000 USDC filled at an average price of approximately 64.9%. This is called “walking the book.” Large orders may experience slippage if liquidity is thin.

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Spread and Liquidity

The spread is the gap between the best bid and best ask.
SpreadMeaning
Tight (0.1-0.5%)High liquidity, active market, low trading cost
Medium (0.5-2%)Normal liquidity, moderate trading cost
Wide (2%+)Low liquidity, higher trading cost, use limit orders
Example:
  • Best bid: 62%
  • Best ask: 64%
  • Spread: 2%
If you market buy and immediately market sell, you lose 2% just to the spread. In tight markets, this cost is much lower.

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Order Validation

Every order is validated before being accepted:
You must have sufficient margin to cover the position if the order fills. Orders that would exceed your available margin are rejected.
The resulting position must stay within the market’s maximum leverage. Orders that would create excessive leverage are rejected.
Orders at extreme prices (far from current market) may be rejected or flagged. This prevents fat-finger errors and manipulation.
Orders must meet minimum size requirements and cannot exceed maximum position limits.

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Matching vs Risk Management

The matching engine and risk engine are separate:
SystemResponsibility
Matching EnginePairs compatible orders, executes trades
Risk EngineEnforces margin, leverage, liquidation rules
The matching engine is “risk-neutral.” It only matches orders. All safety guarantees are enforced by the risk engine independently. Key invariant: No order can be matched unless margin and leverage requirements are satisfied at execution time. If a match would violate risk constraints, it is rejected.

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Why CLOB for Prediction Markets

The orderbook model provides:
  • Transparent pricing: All bids and offers are visible
  • Fair execution: Price-time priority treats everyone equally
  • No slippage from curves: You trade at discrete prices, not along a bonding curve
  • Real depth: You can see exactly how much liquidity exists at each price level
  • Professional compatibility: Market makers and algorithmic traders can participate using familiar infrastructure
This is what allows Ascend to attract the liquidity that prediction markets need.

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Continuous Price Discovery

Prices on Ascend update continuously as orders are placed, matched, and canceled. Every trade prints a new price. Every new limit order changes the orderbook state. The “current price” is always the midpoint between best bid and best ask, or the last traded price. This continuous process is how probability prices evolve in real time as traders express their views.

Next: Settlement & Resolution

Learn how markets resolve and positions settle