> ## 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.

# cannon

> Canonical hub for cannon, the OP Stack fault proof virtual machine — what it does, who runs it, and where its guides, releases, source, and spec live.

cannon is the OP Stack's fault proof virtual machine (FPVM): an onchain MIPS
instruction emulator that lets a disputed L2 state transition be re-executed,
one instruction at a time, on L1.

## Overview

cannon has two halves that must behave identically:

* **Onchain `MIPS64.sol`** — a Solidity implementation of big-endian 64-bit
  MIPS (MIPS64r1) instruction execution, used to verify a single disputed
  instruction on L1.
* **Offchain `mipsevm`** — an instrumented emulator of the same
  instruction set that runs the full program and produces the witness data
  needed to repeat any one step onchain.

The program cannon executes is the fault proof program,
[kona-client](/releases/kona-client), compiled to a MIPS ELF binary; the
[kona-host](/releases/kona-host) binary runs alongside as the preimage
server that supplies chain data during execution. Together they make fault
disputes resolvable: participants bisect an execution trace down to a single
MIPS instruction, and that one instruction is proven onchain.

**Who runs it:** dispute game participants, not everyday node operators.
[op-challenger](/op-stack/fault-proofs/challenger) invokes the cannon binary
automatically when a fault dispute reaches the execution-trace stage, and
chain operators build cannon prestates when configuring permissionless fault
proofs. For how cannon fits into the dispute game, see the
[fault proofs explainer](/op-stack/fault-proofs/explainer) and the
[Cannon](/op-stack/fault-proofs/cannon) and
[MIPS](/op-stack/fault-proofs/mips) deep-dive pages.

## Get started

* [Cannon usage](https://github.com/ethereum-optimism/optimism/tree/develop/cannon#usage)
  — the in-repo README walks through building cannon, loading a kona-client
  ELF into an initial VM state, and running the emulator.

## How-tos

* [Generating absolute prestate and preimage files](/chain-operators/tutorials/absolute-prestate)
  — build and verify the cannon prestate of kona-client that op-challenger
  runs at dispute time.
* [Generating a custom kona-client absolute prestate](/chain-operators/tutorials/kona-custom-prestate)
  — the same, for chains not yet in the public Superchain Registry.

## Configuration & flags reference

* cannon has no configuration reference page on this site yet; it is
  configured entirely through CLI flags, documented by `cannon --help` and
  the [in-repo README](https://github.com/ethereum-optimism/optimism/tree/develop/cannon#usage).

## Releases

* [cannon release tags on GitHub](https://github.com/ethereum-optimism/optimism/releases?q=cannon%2Fv\&expanded=false)
  — cannon does not have a page under [Releases](/releases) yet.

## Source & spec links

* [Source: `cannon/`](https://github.com/ethereum-optimism/optimism/tree/develop/cannon)
  in the Optimism monorepo; the onchain contracts live in
  [`packages/contracts-bedrock/src/cannon`](https://github.com/ethereum-optimism/optimism/tree/develop/packages/contracts-bedrock/src/cannon).
* [Cannon overview docs](https://github.com/ethereum-optimism/optimism/blob/develop/cannon/docs/README.md)
  — in-repo documentation of the onchain/offchain split and the witness
  data (packed state, memory proofs, preimage data).
* [Cannon fault proof VM specification](https://specs.optimism.io/fault-proof/cannon-fault-proof-vm.html)
  — the normative definition of the VM.