Building Production MCP Servers: Architecture, Tool Design, and Distribution Originally published on the BuyWhere Engineering Blog . Read the full deep-dive there. Your MCP server works in development. It passes the mcp inspect smoke test. You've shipped to npm. Then... silence. No installs. No issues. No feedback. Just a package floating in the npm void. This is the gap between "building an MCP server" and "shipping one that developers actually discover and use." Over the past month, we shipped BuyWhere MCP Server — an agent-native commerce API — from zero to 1,700+ daily npm downloads . The Three-Layer Architecture After iterating on BuyWhere's MCP server through 12 releases, we've settled on a three-layer architecture: Layer 1: Tool Definitions — The agent's interface. Tool descriptions are your SEO for AI agents. LLMs decide which tool to call based on description text. Layer 2: Transport — Stdio for local, HTTP/SSE for remote, WebSocket for streaming.…