A tool call is an AI assistant invoking one specific action that an MCP server has advertised. The server lists what it can do, the assistant picks one item from that list, and the call runs with whatever arguments the task needs.
When your agent publishes a Birta site, that is a tool call: one request, naming the project and the files, answered with the address the site now lives at. Reading your version history or rolling one back are separate tool calls on the same connection.
For the full list of what a server can offer beyond tools, see what MCP is and why it matters for publishing.