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kona-host is the OP Stack’s fault proof host program: a native Rust binary, built as part of the Kona project, that runs the preimage server supplying chain data to kona-client while it executes.

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Overview

kona-client runs with no network access, so it cannot fetch chain data itself: everything it reads arrives as a preimage requested by key over the preimage oracle ABI. kona-host is the other end of that channel. It fetches the requested data (L1 headers, transactions, receipts, blobs, L2 state) from its configured L1, L1 beacon, and L2 endpoints, responds to the client’s hints so the right preimages are ready when asked for, and serves them back. Without it, the fault proof program would have no way to learn the chain state it is asked to verify. kona-host runs in single mode (one pre-interop chain) or super mode (an interop superchain cluster), and its preimage server starts in one of two ways: server mode, where it only serves preimages to a client program run by an FPVM (when cannon executes kona-client, it launches kona-host as a subprocess, passing the host command after a -- separator on cannon run), and native mode, where kona-host runs kona-client itself in a native process, useful for witness generation and testing. Who runs it: dispute game participants, indirectly: op-challenger’s --cannon-kona-server flag points at a kona-host binary, which cannon launches when a fault dispute reaches the execution-trace stage. Developers also run it directly in native mode to execute kona-client without an FPVM.

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Get started

  • kona-host usage: the in-repo README documents the host modes, the preimage server modes, and the CLI surface.

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How-tos

  • Run a fault-proof challenger: stand up an op-challenger deployment, including pointing --cannon-kona-server at a kona-host build that matches the configured prestate.
  • Spin up challenger: configure op-challenger for a new chain, including where to get the kona-host binary it needs.

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Configuration & flags reference

  • kona-host has no configuration reference page on this site yet; it is configured entirely through CLI flags, documented by kona-host --help and the in-repo README.

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Releases