> ## Documentation Index
> Fetch the complete documentation index at: https://docs.optimism.io/llms.txt
> Use this file to discover all available pages before exploring further.

# kona-client

> Canonical hub for kona-client, the OP Stack fault proof program, covering what it does, who runs it, and where its guides, releases, source, and spec live.

kona-client is the OP Stack's fault proof program: a Rust program, built as
part of the [Kona](/rust/kona/intro/overview) project, that executes the L2
state transition so a disputed output root can be verified inside a fault
proof VM.

## Overview

kona-client derives the disputed span of the L2 chain from L1 data,
re-executes its blocks, and checks the result against the claimed L2 output
root. It runs sandboxed, with no network access: every piece of chain data it
consumes (L1 headers, transactions, receipts, blobs, L2 state) arrives
through the preimage oracle ABI, served by its companion host process,
[kona-host](/op-stack/components/kona-host). It is built so that the same
inputs produce not only the same outputs but the same execution trace.

That determinism is what makes fault disputes resolvable. For dispute games,
kona-client is compiled to a big-endian 64-bit MIPS (MIPS64) ELF binary and
run inside the [cannon](/op-stack/components/cannon) FPVM; this pairing backs
the `CANNON_KONA` dispute game (game type 8), the respected game type for
permissionless fault proofs since [Upgrade 19](/notices/upgrade-19). Because
every honest participant computes the identical execution trace, a dispute
can be bisected down to a single MIPS instruction and that one instruction
proven on L1.

kona-client succeeded op-program, the Go fault proof program behind the
legacy `CANNON` (game type 0) and `PERMISSIONED_CANNON` (game type 1) games;
op-program has reached end of support (see
[End of Support for op-geth and op-program](/notices/op-geth-deprecation)),
and the kona binaries are the maintained fault proof program today.

**Who runs it:** nobody invokes it by hand in production.
[op-challenger](/op-stack/fault-proofs/challenger) runs cannon when a fault
dispute reaches the execution-trace stage, and cannon executes the
kona-client ELF committed to by the chain's absolute prestate. Chain
operators pin that prestate when configuring fault proofs; developers can
also run kona-client natively through kona-host for testing.

## Get started

* [Generating absolute prestate and preimage files](/chain-operators/tutorials/absolute-prestate):
  build and verify the absolute prestate, the onchain commitment to a
  specific kona-client build, whose preimage op-challenger runs at dispute
  time.

## How-tos

* [Generating a custom kona-client absolute prestate](/chain-operators/tutorials/kona-custom-prestate):
  build a kona-client that embeds a chain configuration not yet in the
  public Superchain Registry.
* [Switch to Kona Proofs](/chain-operators/guides/features/switching-to-kona-proofs):
  move an existing chain's respected game type to the Kona-based fault
  proofs.
* [Run a fault-proof challenger](/use-cases/run-a-fault-proof-challenger):
  stand up the op-challenger deployment that exercises kona-client, from
  prestate selection through configuration and monitoring.

## Configuration & flags reference

* kona-client has no configuration reference page and no operator-facing
  flags. Its inputs (the L1 head, the disputed output roots, the chain
  configuration) arrive as bootstrap data over the preimage oracle, as
  defined in the
  [fault proof program specification](https://specs.optimism.io/fault-proof/index.html#fault-proof-program).

## Releases

* [kona-client release history](/releases/kona-client)

## Source & spec links

* [Source: `rust/kona/bin/client`](https://github.com/ethereum-optimism/optimism/tree/develop/rust/kona/bin/client)
  in the Optimism monorepo.
* [Fault proof program development](/rust/kona/sdk/fpp-dev/intro): the Kona
  book chapter on how fault proof programs like kona-client are structured
  (prologue, execution, epilogue) and built on the Kona SDK.
* [Fault proof program specification](https://specs.optimism.io/fault-proof/index.html#fault-proof-program):
  the normative definition of the program's prologue, main content, and
  epilogue.