What is rustpad-mcp?

rustpad-mcp is a Model Context Protocol server for Rustpad, the efficient, minimal, self-hosted collaborative text editor. It lets an AI assistant read pads, create them, append to them, search-and-replace inside them, and set their editor language — against your own instance.

Why it exists

Rustpad's HTTP surface is read-only: GET /api/text/{id} and GET /api/stats. Everything that changes a pad happens over a WebSocket speaking an operational-transformation (OT) protocol. rustpad-mcp implements enough of that protocol to act as a well-behaved client:

• Edits are operations, not overwrites. append_to_document and replace_in_document retain every character they do not touch. If a human is typing in the same pad at the same moment, the Rustpad server transforms the two edits against each other and both land.
• Positions are Unicode code points. Rustpad counts characters the way Rust does, not the way JavaScript strings do — the server gets this right, emoji and all, and rejects text that cannot survive the trip (unpaired surrogates).
• The model is a visible collaborator. While editing, the server announces itself as rustpad-mcp, so anyone with the pad open sees who is typing.

What Rustpad is — and is not

Two properties of Rustpad shape everything this server does:

• Pads are ephemeral. Documents live in the Rustpad server's memory and are lost on restart and after 24 hours without an open connection (unless the instance runs with SQLITE_URI persistence). The tools say so in their results; treat pads as shared scratch space, not storage.
• There is no authentication. Anyone who can reach the instance and knows a pad id can read and write it. That makes every pad untrusted input — see Security for what the server does about it.

The tool set

Eight tools: three read (get_document, get_document_info, get_stats) and five write (create_document, set_document, append_to_document, replace_in_document, set_language). The full list with parameters is in the tools reference.