Model Context Protocol server: a meta-tool that exposes a list of tools the LLM can discover and invoke, so only relevant ones consume context budget. Increasingly popular, with multiple Ruby implementations that can expose data from real applications to LLMs. Major caveat Hasiński flags: MCP servers come with no built-in security checks — any MCP server can break your model, so using one is essentially handing someone else control of your LLM.