> ## 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.

# Solvers

> Understanding CoW Protocol solvers - off-chain agents that discover optimal batch auction solutions

# Solvers

Solvers are critical infrastructure in CoW Protocol -- off-chain agents that monitor the order pool for new and existing orders and compute optimal settlements by finding clearing prices and trade routes.

## Key Responsibilities

Solvers perform five primary functions:

1. **Monitor** incoming orders from the order pool
2. **Calculate** optimal trade settlements and clearing prices
3. **Access liquidity** from various sources (AMMs, aggregators, private inventory)
4. **Submit** settlement transactions on-chain
5. **Earn fees** upon successful execution

## Authorization and Security

Only approved solvers can call the settlement function through the `GPv2AllowListAuthentication` contract, which maintains an allowlist managed by a designated manager role.

```solidity theme={null}
modifier onlySolver {
    require(authenticator.isSolver(msg.sender), "GPv2: not a solver");
    _;
}
```

<Warning>
  The manager role has significant power over the protocol. It should be assigned to a multi-sig wallet or DAO.
</Warning>

## Competition Mechanism

Multiple solvers submit solutions simultaneously, and these are ranked by:

* **Trader surplus generated** - How much better the execution is compared to limit prices
* **Number of orders filled** - More filled orders is preferred
* **Gas efficiency** - Lower gas consumption for the same outcome
* **Execution success probability** - Likelihood of on-chain execution success

## Solver Economics

### Revenue Sources

* Protocol fees
* Surplus capture (executing at better prices than order limits)
* CoW finding (matching orders directly without external liquidity)
* Arbitrage opportunities

### Risks

* Transaction failures (gas costs without revenue)
* MEV extraction by block builders
* Price slippage between solution computation and on-chain execution
* Competition from other solvers

## Technical Details

Solvers interface with external liquidity sources through standardized interaction structures supporting three execution phases:

```typescript theme={null}
// Pre-settlement: Setup operations
const preInteraction = {
  target: "0x...", // e.g., approve token
  value: 0,
  callData: "0x...",
};

// Intra-settlement: Trading operations
const intraInteraction = {
  target: "0x...", // e.g., Uniswap swap
  value: 0,
  callData: "0x...",
};

// Post-settlement: Cleanup operations
const postInteraction = {
  target: "0x...", // e.g., unwrap WETH
  value: 0,
  callData: "0x...",
};
```