marginal is a Model Context Protocol (MCP) server: Email A/B tests for AI agents: subject lines, managed sends, open/click tracking, and results. As an MCP server it plugs straight into AI assistants, exposing its functionality as tools the model can invoke on your behalf.
It's a hosted (remote) server — point your client at https://marginal.sh/mcp and you're connected, with nothing to install locally. The current release is v0.3.0.
You'll find marginal in the AI & Agents category here on mcp.site; it connects to Claude Desktop, Claude Code, Cursor, VS Code, Windsurf, Zed, and any other MCP client — see the install snippets below. If you maintain marginal for marginal.sh, claim this listing to verify ownership, earn the Verified badge, and keep the details current.
