> ## Documentation Index
> Fetch the complete documentation index at: https://docs.cow.bleu.builders/llms.txt
> Use this file to discover all available pages before exploring further.

# Swap Guards

> Implement the ISwapGuard interface to restrict which programmatic orders can settle via CoW Protocol.

# Swap Guards

Swap Guards implement the `ISwapGuard` interface to restrict which programmatic orders can settle via CoW Protocol. They provide an additional layer of security and control over programmatic orders by validating orders during settlement verification.

## How Verification Works

During order processing, ComposableCoW checks if an owner has configured a guard. If present, the guard's `verify` function must return `true` to permit settlement. The verification receives four parameters:

| Parameter       | Description                                                                         |
| --------------- | ----------------------------------------------------------------------------------- |
| `order`         | Complete `GPv2Order.Data` struct with all settlement details                        |
| `ctx`           | Context identifier (`bytes32(0)` for merkle trees or `H(params)` for single orders) |
| `params`        | Programmatic order configuration data                                               |
| `offchainInput` | Dynamic off-chain data for order generation                                         |

If verification fails, settlement triggers a `SwapGuardRestricted` error.

## Implementation Pattern

Guards should extend `BaseSwapGuard` for ERC165 interface support. The `ReceiverLock` example demonstrates restricting orders so funds return only to the owner (receiver address `0x0` in GPv2 terminology means "self").

## Practical Applications

* Preventing fund transfers to external addresses
* Restricting trading to whitelisted token pairs
* Enforcing time-window limitations
* Setting transaction size or volume caps

## Important Constraints

Guard implementations must be:

* **Gas-efficient** since they execute during signature verification
* **Deterministic** providing the same results for the same inputs (they execute as view functions)
* They cannot reliably depend on mutable external state

## Setup and Management

* Activate guards via `setSwapGuard()`
* Disable them by passing `address(0)` to the same function