How does a format command built with MCP prompts work?

A practical example is a format command that converts documents to markdown. The user-facing workflow looks like this: the user types a slash to see the available commands, selects format, and specifies a document ID. The client then asks the MCP server for the format prompt with that document ID as an argument. The server fills the document ID into the prompt template and returns the resulting messages. The client sends those messages to Claude. Claude reads and reformats the document using the available tools. The user gets back clean markdown with proper headers, lists, and formatting, all from a single slash command.