Market Microstructure Guide

The spread is the price of immediacy — what the market maker charges to bear adverse selection risk right now. Huang & Stoll (1997) decomposed it into adverse selection, inventory, and order processing costs, which is why a widening spread is diagnostic, not just expensive. But the average hides the regime change: a bar with mean spread of 2 bps that was 0.5 bps for 55 seconds and 8 bps for 5 seconds tells a fundamentally different story than a steady 2 bps. Bollerslev & Melvin (1994) showed spread volatility itself predicts future return volatility — the instability of the spread matters as much as its level.

• Quoted spread — The gap between best ask and best bid. The sticker price of trading — what you see, not necessarily what you get once real size hits the book.
• Spread in basis points — Price-normalized spread for cross-asset comparison. A 1-cent spread means something very different on a $10 asset versus a $50,000 one.
• Top-of-book depth — How much size sits at the best prices. A 1 bps spread on 50k of depth is a different market than 1 bps on 500k. This tells you the cost of the first fill — not whether the market survives the second.
• Spread/depth ratio — The honesty check on tight spreads. Low ratio means genuinely cheap liquidity. High ratio means the narrow quote is decorative — it will not survive contact with real flow.

Cont, Kukanov & Stoikov (2014) showed it clearly: order book imbalance predicts the direction of the next mid-price change, and the relationship is monotonic — stronger lean, larger expected move. The mechanism is straightforward. When one side is substantially thicker, the thinner side depletes first and the midpoint shifts. But the real insight is in the layers. L1 and L2 can tell contradictory stories, and the divergence between them is often more informative than either alone.

• L1 imbalance — Best-bid versus best-ask quantity. A single snapshot is noisy; time-averaged imbalance over the interval is what actually predicts.
• L2 imbalance — The same signal extended across 5, 10, 20, and 25 levels per side. Captures the full shape of supply and demand behind the frontier — L2 can be draining even while L1 looks stable.
• L1-L2 divergence — Where the actionable signal lives. Thin L1 bids with deep L2 behind them is a market maker repositioning, not genuine weakness. Thick L1 bids with nothing behind them is a single concentrated quote — pull it and there is a gap.
• Weighted midprice — Stoikov (2018) showed the quantity-weighted midprice — shifted proportional to size at each side — beats the simple midpoint as a predictor of the next transaction price.

Not all trades carry the same information. Barclay & Warner (1993) found that medium-sized orders — not the largest — account for a disproportionate share of cumulative price impact. Informed traders deliberately size down to avoid detection. This means aggregate volume alone is insufficient: you need to decompose flow by direction, size, and concentration to understand what it is actually telling you.

• Volume delta — Buy-initiated minus sell-initiated volume. The directional pulse of the market — the net pressure that moved through the book over the interval.
• Buy/sell ratio — The participation rate by side. A ratio that stays skewed across multiple bars is sustained pressure, not noise. Brief spikes wash out; persistent skew does not.
• Trade size segmentation — Volume split into small, medium, and large buckets. When the large-trade buy ratio diverges from the small-trade buy ratio, you are seeing disaggregated flow — the classic microstructure signature of informed accumulation happening alongside retail noise.
• Flow toxicity — Rooted in Easley, López de Prado & O’Hara’s VPIN framework. Relates signed net flow to realized volatility. When both are high simultaneously, adverse selection costs spike and spreads should widen — that is when liquidity provision is most dangerous. Low toxicity in a range-bound market means cheap, reliable liquidity. Some instruments attract systematically more toxic flow than others, which matters for cross-asset risk sizing.

Kyle’s lambda and Amihud illiquidity approach the same question from opposite ends: how much does trading move the price? Lambda measures information content per unit of signed flow; Amihud measures return per dollar of volume. Where they agree, the market is behaving consistently. Where they diverge is where the diagnosis gets interesting — rising Amihud without rising lambda points to exogenous volatility, not informed flow. Rising lambda alone means someone in the order flow knows something the quote does not yet reflect.

• Amihud illiquidity — Absolute return divided by dollar volume. When this is high, small trades are moving price disproportionately — the market cannot absorb even modest flow without repricing.
• Kyle lambda — The slope of price change versus signed order flow. Higher lambda means each dollar of directional flow moves the midpoint further — either because liquidity is thin or because the flow carries information the market maker is pricing in real time.
• Directional impact asymmetry — Buy-side and sell-side lambda are rarely equal. Markets often absorb sells more efficiently than buys, especially in trending environments where sell pressure is expected and already priced.
• Slippage — The gap between what the quote promised and what execution delivered. Perold (1988) called it implementation shortfall — the distance between paper portfolio returns and real returns. This is where backtest assumptions meet reality.
• Buy-sell slippage asymmetry — Persistent buy > sell slippage means the market is paying up for demand — accumulation pressure. The reverse means liquidation pressure. Symmetric slippage is the rare condition where both sides face equal friction, indicating a genuinely two-sided market.

In crypto perpetual futures, funding rate, basis, and open interest are the primary indicators of leverage positioning and directional crowding. When funding, basis, and open interest all point the same direction, the market is building a position that will eventually need to unwind.

• Funding rate — The real-time price of directional consensus in leveraged markets. Strongly positive funding means longs are paying to hold, and crowded positioning raises liquidation cascade risk. Strongly negative funding reflects genuine fear.
• Basis (bps) — The perp-spot spread is the marginal cost of leverage.
• Open interest — Total outstanding contracts. Rising OI with rising price means new longs entering. Rising OI with falling price means new shorts are being opened. Declining OI means positions are being unwound — the market is getting lighter regardless of direction.