> ## 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.

# Prologue

The prologue stage of the program is commonly responsible for bootstrapping the program with inputs from an external
source, pulled in through the [Host-Client communication](/rust/kona/sdk/fpp-dev/env#host---client-communication) implementation.

As a rule of thumb, the prologue implementation should be kept minimal, and should not do much more than establish
the inputs for the [execution phase](/rust/kona/sdk/fpp-dev/execution).

## Example

As an example, the prologue stage of the `kona-client` program runs through several steps:

1. Pull in the boot information over the [Preimage Oracle ABI][preimage-specs], containing:
   * The L1 head hash containing all data required to reproduce the L2 safe chain at the claimed block height.
   * The latest finalized [L2 output root][l2-output-root].
   * The [L2 output root][l2-output-root] claim.
   * The block number of the [L2 output root][l2-output-root] claim.
   * The L2 chain ID.
2. Pull in the `RollupConfig` and `L2ChainConfig` corresponding to the passed L2 chain ID.
3. Validate these values.
4. Pass the boot information to the execution phase.

[op-stack]: https://github.com/ethereum-optimism/optimism

[op-program]: https://github.com/ethereum-optimism/optimism/tree/develop/op-program

[cannon]: https://github.com/ethereum-optimism/optimism/tree/develop/cannon

[cannon-rs]: https://github.com/op-rs/cannon-rs

[asterisc]: https://github.com/ethereum-optimism/asterisc

[fp-specs]: https://specs.optimism.io/experimental/fault-proof/index.html

[fpp-specs]: https://specs.optimism.io/experimental/fault-proof/index.html#fault-proof-program

[preimage-specs]: https://specs.optimism.io/experimental/fault-proof/index.html#pre-image-oracle

[cannon-specs]: https://specs.optimism.io/experimental/fault-proof/cannon-fault-proof-vm.html#cannon-fault-proof-virtual-machine

[l2-output-root]: https://specs.optimism.io/protocol/proposals.html#l2-output-commitment-construction

[op-succinct]: https://github.com/succinctlabs/op-succinct

[revm]: https://github.com/bluealloy/revm

[kona]: https://github.com/ethereum-optimism/optimism/tree/develop/rust/kona

[issues]: https://github.com/ethereum-optimism/optimism/issues

[new-issue]: https://github.com/ethereum-optimism/optimism/issues/new

[contributing]: https://github.com/ethereum-optimism/optimism/tree/develop/rust/kona/CONTRIBUTING.md

[op-labs]: https://github.com/ethereum-optimism

[bad-boi-labs]: https://github.com/BadBoiLabs