Your CLI Tool Needs an MCP Server: Shipping One in a Day, Protocol by Hand

Every CLI tool built before 2026 is asking itself the same question: how do AI agents discover me? The answer the ecosystem converged on is the Model Context Protocol — MCP. If Claude Desktop, Cursor, or any MCP-capable client can list your tool's capabilities and call them, your tool exists for agents. If not, it doesn't.

xbrowser is a browser-automation CLI (57 commands, 130+ site plugins, self-healing replay). This week we shipped xbrowser mcp — a stdio MCP server exposing 7 browser tools. This post is the build log: the design decisions, the two real bugs the first smoke run caught, and why we wrote the protocol layer by hand.

Why hand-write the JSON-RPC layer?

The official @modelcontextprotocol/sdk is fine software. We didn't use it, for three reasons that generalize:

Your CLI Tool Needs an MCP Server: Shipping One in a Day, Protocol by Hand

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