An MCP Tool to Measure Email Engagement
If you want an MCP tool to measure email engagement directly from an AI agent, marginal exposes managed sends plus open and click tracking so your assistant can read real results instead of guessing.
What 'measure email engagement' means here
Engagement is only useful if it's tied to a decision. marginal tracks opens and clicks per variant inside a single test, then reports lift between them so you can tell which subject line actually moved the needle.
Because everything runs through the email MCP server, the agent that wrote your subject lines is the same one that reads the numbers — no copy-pasting metrics out of a dashboard.
- Open rate and click rate captured per variant
- Within-test lift so winners are comparable, not absolute
- Results scoped to the experiment your agent launched
The tools that do the measuring
marginal ships four MCP tools. The measurement work mostly happens in get_results, but it only makes sense alongside the tools that create and ship the test.
- generate_variants — draft competing subject lines
- launch_test — run a subject line A/B test with a managed send
- get_results — read opens, clicks, and within-test lift
- recommend_next — turn engagement data into the next experiment
Why agents are good at this
Measuring engagement is repetitive: send, wait, pull metrics, compare, decide. That loop maps cleanly onto AI agent email marketing workflows, where the agent can poll get_results and propose a follow-up without a human babysitting the funnel.
marginal is hosted, so there's no self-managed infrastructure. You point a supported client — Cursor, Claude Desktop, Claude Code, Windsurf, Cline, Continue, Codex, or Zed — at the endpoint and authenticate with a Bearer API key.
Getting started
Connect to https://marginal.sh/mcp, run your first subject line A/B test, and read engagement back through get_results. The free tier covers 100 experiments per month, which is plenty to validate the measurement loop before scaling up.
Full tool schemas and setup steps live in the docs at https://marginal.sh/docs/.
Get started with marginal
marginal is a hosted email marketing MCP server at marginal.sh. Sign up free, create an API key, and connect https://marginal.sh/mcp from Cursor, Codex, or Claude Desktop.
- 100 experiments/month on the free tier
- Four MCP tools: generate_variants, launch_test, get_results, recommend_next
- Listed in the MCP Registry as sh.marginal/mcp