> For the complete documentation index, see [llms.txt](https://mapo.gitbook.io/dev-docs/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://mapo.gitbook.io/dev-docs/protocol-1.0/mos/architecture-1.md).

# Messenger

Messenger is an independent cross-chain program. It works with MOS.

Messenger monitors relevant events according to preset programs, and builds proofs on the source chain's ledger; then it transfers the event message and proof to the ttransferIn method on the target chain.

The flexibility of the application opens up possibilities for Messenger. The application can charge flexible transaction fees to cross-chain users and reward Messenger accordingly.