Protocol released by Anthropic in 2024, based on JSON-RPC, designed for LLMs to invoke tools. LLM-ready in a way REST is not: calling REST tools costs many tokens, whereas MCP is tailored to the model's interaction style and is therefore token-efficient, at the cost of lower raw performance. Paired with LLM runtimes like Claude Code, an MCP server (e.g. built with fast-mcp) can expose tools that the LLM picks and invokes on its own — in the wroclove.rb 2026 demo Emiliano simply writes 'create an order for product ID, customer and shipping address' and Claude finds the right tool, formats currency, and on an unknown product reads the Active Record 'product not found' stack trace and proactively suggests double-checking the product ID.