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Orderbook

The orderbook shows you the actual liquidity behind a market’s price. Before placing a trade — especially a large one — check the orderbook to understand how much you can buy or sell without significant price impact.

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Orderbook ladder

The OrderBookLadder component displays a traditional trading ladder:
ColumnSideColor
Bid SizeLeftEmerald/green background fill
PriceCenterPrice level in cents
Ask SizeRightRose/red background fill
Key features:
  • Shows the top 8 price levels by default
  • Bid and ask sizes are merged by price level from the raw orderbook data
  • Size background fills proportionally — the largest order at any level gets maximum fill width (50% of column)
  • Hover to see cumulative depth at that price level
  • Real-time updates every 5 seconds (background refetch)
How to read it:
  • Large bid sizes (left, green) = strong buy support at that price
  • Large ask sizes (right, red) = selling pressure at that price
  • Gaps in the ladder = thin liquidity, potential for slippage
  • Asymmetric depth (much more on one side) = directional pressure

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Depth chart

The OrderBookDepth component shows cumulative order book depth:
  • Left side: Bids (emerald gradient) — cumulative buy orders from midpoint down
  • Right side: Asks (rose gradient) — cumulative sell orders from midpoint up
  • Horizontal bars: Each bar represents a price level, width proportional to cumulative depth
  • Midpoint: The current market price, displayed at center
How to read it:
  • Steep depth = lots of liquidity concentrated near the current price
  • Gradual slope = liquidity spread across many price levels
  • A “wall” (sudden large step) = a significant resting order at that price

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Spread indicator

The SpreadIndicator component shows the real-time bid-ask spread:
  • Displayed as a number in cents (e.g., “Spread: $0.02”)
  • Tight spread (1-2¢) = healthy, liquid market
  • Wide spread (5¢+) = be careful, consider limit orders

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Data source

Orderbook data is fetched from Polymarket’s CLOB API via the useOrderBook hook:
  • Refresh interval: 5 seconds (background polling)
  • Data: Raw bid and ask levels with cumulative depth calculation
  • Parallel fetches: Orderbook, spread, and midpoint are all fetched simultaneously

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Using the orderbook to trade better

Check the ask side (right) if buying, or the bid side (left) if selling. If your order size is more than ~10% of the visible depth at the best price, you’ll experience slippage. Consider a limit order instead.
The orderbook is the ground truth of a market. Price charts show where the market has been; the orderbook shows where the market IS. Always check depth before sizing up on a trade.