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Collateral Rail is a Uniswap v4 settlement system for markets that need normal AMM liquidity plus controlled off-pool settlement capacity.

The pool still behaves like a pool. The extra machinery only wakes up when a swap intentionally carries signed settlement material.

System Components

These are the pieces you will see repeated across the docs. The important part is not memorizing every contract. It is knowing which component owns the decision you are looking at.

First, The Shape

The system is not a binary switch between issuer capacity and pool liquidity. The quote server chooses the allocation and signs the settlement envelope. The SDK carries it into the hook as signed hookData, and the hook verifies risk before executing the quote-selected controlled leg exactly.

That is the core mental model:

• Pool liquidity only: if controlled settlement is not used, the pool can handle the whole swap.
• Controlled capacity only: issuer, vault, or controller capacity can settle the whole eligible amount when risk checks allow it.
• Mixed allocation: the quote server can allocate across controlled capacity and pool liquidity, for example when issuer capacity covers part of the balance and the pool handles the remainder.
• Reader takeaway: signed flow is not just a second lane; it is an allocation problem constrained by quote bounds, risk policy, and available liquidity.

What To Remember

One Signed Swap, Illustrated

This is the story most integrators need first:

1. Build The Executable Quote

2. Enter The Hook And Allocate

3. Settle And Close

The quote is not a vague offchain promise. It is a bounded envelope: signer, trader, pool, amount, price, expiry, and replay identity all have to line up. The router checks that envelope before the swap starts; the hook then uses it during beforeSwap and afterSwap to size controlled settlement, leave any remainder to the pool, and consume replay state exactly once.

The Four Planes

Use this map when you are trying to place a file, script, or page in your head. The control plane is drawn as a wrapper because it is not a late-stage check; it constrains every request, quote, and settlement action.

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