Limit order book simulator
Read the book, predict the fill, watch the shares trade. See what a market order really costs once it walks through several price levels, and practise working a larger order over time.
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How to use it
Each level of the book shows a price and the quantity available there. Predict the average price of a market order before you send it. For example, if sellers offer 10 shares at $100.10 and 20 at $100.20, a market buy of 25 shares averages $100.16.
In the execution exercise you must buy or sell a target of up to 200 shares before a deadline. You can rest limit orders, replace them or wait. At the deadline, remaining shares trade at available prices and anything still unfilled incurs a $1 per share penalty. Costs are measured against the starting mid.
What it teaches
The quoted spread is only the start of trading cost. Larger orders consume depth and move the average price, and waiting trades price impact against the risk that the market moves away. The tool estimates execution quality, not future trading profit; fees and margin are omitted.