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Solver Engine API

The Solver Engine API enables route optimization services within CoW Protocol. These engines receive auction data and return abstract solutions without handling calldata encoding, transaction simulation, or settlement submission.

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Core Responsibilities

Solver engines focus on four main functions:
  1. Route Finding - Determining optimal paths through liquidity
  2. Order Matching - Identifying coincidence of wants between orders
  3. Price Discovery - Computing uniform clearing prices
  4. Constraint Satisfaction - Respecting order limits and balance rules

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Solver Types

CoW Protocol provides internal solvers (Baseline, Balancer, Legacy) while supporting external providers including 1inch, 0x, ParaSwap, and custom implementations.

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API Endpoints

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POST /solve

Receives auction data and returns one or multiple solutions. Key parameters include:
  • tokens: Token address mappings with decimals, symbols, reference prices
  • orders: Array of CoW Protocol orders requiring solutions
  • liquidity: Available on-chain liquidity sources
  • effectiveGasPrice: Current gas pricing in Wei
  • deadline: ISO 8601 timestamp for solution delivery
Response includes: Solution ID, uniform clearing prices, trades, interactions, and gas estimates.

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POST /notify

Receives performance feedback on solutions, with notification types including:
  • success: Solution settled on-chain
  • simulationFailed: Solution reverted during testing
  • timeout: Solution missed deadline
  • banned: Solver has been restricted

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Solution Requirements

Solutions must satisfy:
  • Order Limits: Executed amounts respect sell/buy constraints
  • Uniform Prices: All trades use identical price vectors
  • Token Conservation: Total inputs equal outputs per token
  • Fee Application: Proper surplus, volume, and price improvement fee calculations

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Scoring Formula

Score = sum(user_surplus) + sum(protocol_fees) - gas_cost_in_native_token

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Fee Policies

Three fee types apply:
  1. Surplus Fee: Charge factor x surplus, capped at maxVolumeFactor x volume
  2. Volume Fee: Factor multiplied by executed volume
  3. Price Improvement Fee: Factor applied to improvement over quoted prices

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Best Practices

  • Respect solution deadlines consistently
  • Validate input data thoroughly
  • Apply fee policies with precision
  • Provide accurate gas estimations
  • Handle partial fills appropriately
  • Test constraints before returning solutions

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Resources

Last modified on March 4, 2026