Solver
A solver (also called a filler) is an entity in intent-based and OFA architectures that competes to fulfill user intents at the best possible execution. Solvers run optimization algorithms to find the cheapest execution path for a user's trade — sourcing from on-chain AMMs, their own inventory, CEXs, or other solvers — and bid for the right to execute the trade via an auction mechanism. The solver profits from the spread between the user's limit price and the execution price they achieve. Solver competition is structurally similar to builder competition in PBS: multiple solvers race to provide the best outcome, and the winner's margin is compressed by competition. Top solvers invest heavily in latency optimization, liquidity discovery, and gas estimation to win auctions. The role of the solver has become a professional category in DeFi, sitting alongside the searcher and builder as one of the core MEV-economic actors.