> ## 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.

# Contracts Overview

> Core architecture and components of the CoW Protocol smart contract system

# Contracts Overview

CoW Protocol (Gnosis Protocol v2) is a decentralized trading protocol that leverages batch auctions and coincidence of wants to provide optimal trade execution.

## Core Contracts

### GPv2Settlement

The central orchestration contract handling order validation, batch settlements, and Balancer Vault coordination.

* Validates order signatures and parameters
* Executes batched trades at uniform clearing prices
* Manages pre/intra/post-settlement interactions
* Inherits from `GPv2Signing`, `ReentrancyGuard`, and `StorageAccessible`

### GPv2VaultRelayer

A relayer for Balancer Vault interactions and token transfers.

* Transfers tokens from user accounts to the settlement contract
* Executes batch swaps through Balancer pools
* Restricted to settlement contract access only

### GPv2AllowListAuthentication

Manages solver authorization via an allowlist mechanism.

* Maintains a mapping of authorized solver addresses
* Managed by a designated manager role
* Supports proxy-based upgradeability

## Key Libraries

| Library             | Purpose                                                                     |
| ------------------- | --------------------------------------------------------------------------- |
| **GPv2Order**       | EIP-712 order hashing and UID management                                    |
| **GPv2Trade**       | Trade encoding/decoding with compact flag representation                    |
| **GPv2Interaction** | Settlement interaction hooks for arbitrary contract calls                   |
| **GPv2Signing**     | Multi-scheme signature verification (EIP-712, eth\_sign, EIP-1271, PreSign) |

## Deployment Order

1. **Authentication contract** is deployed first (with proxy)
2. **Settlement contract** is deployed with the authenticator address
3. **VaultRelayer** is auto-deployed by the settlement contract constructor

## Three-Phase Settlement

```mermaid theme={null}
sequenceDiagram
    participant Solver
    participant Settlement
    participant VaultRelayer
    participant External

    Solver->>Settlement: settle()
    Settlement->>External: Pre-interactions
    Settlement->>VaultRelayer: transferFromAccounts()
    Settlement->>External: Intra-interactions
    Settlement->>External: transferToAccounts()
    Settlement->>External: Post-interactions
```

## Security Features

* **Reentrancy protection** via `ReentrancyGuard`
* **Solver authorization** via `onlySolver` modifier
* **Order validation** including signature, expiry, and price checks
* **Interaction restrictions** preventing calls to VaultRelayer

## Gas Optimizations

* Assembly usage for low-level operations
* Storage refunds for expired order cleanup
* Compact trade encoding reducing calldata costs
* Memory reuse across settlement operations