Reading the orderbook

Most retail traders look at a chart. The chart is a downstream artifact. The thing that's actually happening — the live, twitching mechanism that produces the chart — is the orderbook. Once you can read it, the chart starts to feel like the shadow on a wall instead of the action itself.

What an orderbook is

An orderbook is a list of every unfilled buy and sell order on a particular trading pair, sorted by price. The buys (bids) are below the current price; the sells (asks) are above it. The gap between the highest bid and the lowest ask is the spread.

    PRICE      SIZE      SIDE
    87,455      2.10      ASK
    87,440      0.85      ASK
    87,420      4.30      ASK
    -- spread --
    87,395      1.20      BID
    87,380      3.10      BID
    87,370      0.90      BID

When a buy order arrives that's willing to pay 87,455 or more, it eats the 2.10 BTC sitting at that price level and the price ticks up. When a sell order arrives willing to take 87,395 or less, it consumes that bid and the price ticks down. The chart you watch is the price of the most recent trade, plotted over time.

Two kinds of orders

• Limit orders sit in the book at a specific price, waiting for someone to fill them. They make the book — they are 'maker' orders.
• Market orders arrive and immediately consume liquidity at whatever price is available. They take from the book — they are 'taker' orders.

Most exchanges charge takers more than makers in fees. The exchange wants you to leave liquidity in the book, not remove it.

Depth

Depth is how much volume sits within some distance of the current price. Deep books absorb large orders without much price movement. Thin books are fragile — a single 50 BTC market buy can rocket the price 2% on a thin altcoin pair.

When you place a market order larger than the top level, you 'walk the book' — your order eats through level after level, paying progressively worse prices. The difference between the price you expected and the price you actually got is slippage.

Estimating slippage

Most exchange APIs let you fetch the current orderbook. Walking it manually for, say, a $100k buy on BTC/USD will tell you exactly what slippage to expect. For most major pairs the answer is 'basically none.' For mid-cap altcoins on a single venue, it can be alarming.

Patterns and what they actually mean

Walls

A 'wall' is a single huge order at one price level, often visible on the depth chart as a vertical cliff. Walls are sometimes real — a fund placing a large limit order — and sometimes spoofed, placed to scare off the other side and pulled before they execute. Spoofing is illegal in regulated venues but trivial on most crypto exchanges.

Iceberg orders

Big traders don't want their full size visible because it would move the market against them. Iceberg orders show only a small portion of the total at any time, refilling automatically as it gets eaten. If you watch a level get bid 0.5 BTC at a time over and over, that's probably an iceberg — there's a much bigger buyer behind it.

Tape reading

The trade tape is the chronological list of executions: time, price, size, side. Watching it during volatile periods is more informative than any chart. Aggressive sequences of taker buys at the ask, growing in size — that's pressure. A sudden gap with no trades, then a print 1% lower — somebody just wiped the bid stack.

Why this matters even if you don't trade

Liquidity is what determines whether you can actually exit a position at the price you see on the screen. The screen shows last trade. Last trade is one tiny order. Your exit is much bigger than that. If the book under you is thin, the screen price is a lie.

Aggregation across venues

Crypto liquidity is fragmented across dozens of venues. Real institutional execution doesn't happen against any single book — it happens via aggregators that route slices of the order across many venues simultaneously, plus OTC desks for the largest blocks. The 'true' price at any moment is a weighted average across enough venues to count as a market.

For retail purposes, picking a single deep venue (Coinbase, Kraken, Binance) for a major pair is almost always good enough. Just be aware that the book you're looking at is a fragment, not the whole.