Reading Level 2 Market Data
Level 2 market data shows the full depth of the order book, all visible buy and sell orders at each price level, along with the size and the exchange or market maker posting them. While Level 1 data shows only the best bid and ask (the national best bid and offer, or NBBO), Level 2 reveals the supply and demand landscape behind those prices.
Understanding the Order Book
The order book displays two sides:
Bid Side (Buyers): All resting buy orders arranged from highest to lowest price. The top of the bid book is the best bid, the highest price someone is willing to pay. Below it are additional buy orders at progressively lower prices, representing levels where buyers are willing to step in.
Ask Side (Sellers): All resting sell orders arranged from lowest to highest price. The best ask is the lowest price someone is willing to accept. Above it are sell orders at higher prices.
The Spread: The difference between the best bid and best ask is the spread. Tight spreads (one cent in liquid stocks) indicate high liquidity and competition among market makers. Wide spreads indicate lower liquidity and higher transaction costs.
What Level 2 Reveals
Depth of Market: The total size available at each price level indicates how much buying or selling pressure exists. A bid side showing 50,000 shares at the best bid versus 5,000 shares at the best ask suggests immediate buying pressure exceeds selling pressure at current prices.
Stacked Orders: When large orders (relative to the stock's average) accumulate at a specific price level, they create potential support (on the bid side) or resistance (on the ask side). These levels often correspond to round numbers or technically significant prices.
Order Book Imbalance: Calculating the ratio of total bid size to total ask size across several levels provides an imbalance metric. Persistent imbalance toward the bid side is associated with short-term upward price pressure, and vice versa.
Reading Market Maker Activity
In Nasdaq-listed stocks, Level 2 displays market maker identifiers (MPIDs) alongside their quotes. Certain market makers have developed reputations for their behavior:
Size at the Top: Market makers consistently posting large sizes at the best bid or ask are actively providing liquidity. Their presence stabilizes the price at that level. If a major market maker suddenly pulls their bid, it can signal an impending downward move.
Stepping Away: When multiple market makers widen their quotes simultaneously, it signals uncertainty or anticipation of a large order or news event. This "thinning" of the book can precede volatile moves.
Limitations of Level 2
Iceberg Orders: Large institutional orders are often displayed as small visible quantities (e.g., showing 100 shares while the actual order is 50,000). The visible order book is therefore an incomplete picture of true supply and demand.
Spoofing Remnants: Although illegal, the practice of placing and quickly canceling large orders to create false impressions of supply or demand has influenced how traders view Level 2 data. Not all large visible orders will actually be executed, some may be pulled before they can be filled.
Dark Pool Diversion: A significant percentage of institutional order flow executes in dark pools, never appearing on the visible order book at all. Level 2 shows only the lit market, which may represent a minority of actual trading interest. The aggregate off-exchange measure we publish free is the dated DIX reading, from the published series.
Speed: The order book changes hundreds of times per second in active stocks. What you see on your screen is a snapshot that may already be stale. High-frequency traders exploit this latency, making Level 2 less reliable as a real-time indicator for manual traders.
Practical Application
Despite its limitations, Level 2 provides valuable context:
Entry Timing: Ask-side depth shows how much displayed supply sits above the current price. Thin asks mean less displayed resistance to upward movement.
Stop Placement: Visible bid size is one reference point for stops. If 100,000 shares are stacked at $49.90, a stop at $49.85 sits behind that displayed size, although displayed size can be pulled before price reaches it.
Confirmation Tool: Order book dynamics can be read alongside other signals, for example whether bullish options flow coincides with bid-side dominance in the stock's book.
Execution Quality: Understanding Level 2 helps you place limit orders more effectively, improving fill rates and reducing slippage.