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Arbitrating auctions

This section gives a high level overview of the different components that are involved for CoW protocol batch auctions to take place.


Three main sub-systems are required to facilitate and drive the auction

Order book

The orderbook is the main entry point of the protocol for traders. Using the orderbook's API, UIs and other integrations allow traders to:

  • Get quotes for orders
  • Place orders
  • Cancel orders
  • Get the currently solved auction
  • Etc.

For instance, when you visit CoW Swap and place an order, the site uses the Order book API to add the order to a database. This database with all orders is shared with the autopilot.


The autopilot is a service that drives the core protocol functionalities with responsibilities including:

  • Creating and arbitrating auctions
  • Defining the timeline and valid orders for each auction
  • Orchestrating the revelation and settlement of the winning solver's solution
  • Monitoring the competition
  • Serving as data consensus layer in the case of dispute or slashing by the DAO
  • Communicating auctions to all registered solvers


For the sake of this documentation, we differentiate solvers into two sub-parts:


The Driver is the executive part of the solving process, and is responsible for:

  • Interacting with the blockchain in order to enrich, encode and eventually execute the settlement
  • Preparing all the data needed for the engine to match orders in the auction and forwarding the augmented auction to the engine
  • Receiving raw solutions from the solver engine, which it post-processes, simulates, merges, encodes into a blockchain transaction and finally scores

The driver interfaces with the autopilot and reports the best solution's score to participate in the competition. If chosen as a winner of the auction, the driver is also responsible for getting the solution included in the blockchain.

Solver Engine

Solver Engines implement the pure matching logic, by employing different types of solving algorithms to optimally match traders with one another taking on-chain as well as private liquidity into account. They receive the pre-processed auction instance from the driver sub-component and return the solution together with instructions on how to achieve the fulfillment on-chain.