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.

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

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

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:

// 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...",
};