Email Marketing Without the Mailchimp API
You don't need to provision a Mailchimp API key, glue together SDKs, and babysit webhooks just to test subject lines. marginal is a hosted email MCP server that lets an AI agent generate variants, launch tests, and read results directly — no third-party marketing API required.
Why skip the Mailchimp API entirely
Traditional email marketing stacks assume you'll integrate a platform API, manage list IDs, and write custom code to interpret campaign reports. That's a lot of plumbing before you ever ship a single experiment.
With marginal, the work happens through MCP tools your agent already understands. The result is email marketing without Mailchimp API setup — you point your assistant at the server and it handles generation, sending, and measurement.
- No platform API key to rotate or scope
- No campaign report parsing or webhook handling
- Managed sends with built-in open and click tracking
- Within-test lift metrics returned straight to your agent
How a subject line A/B test works in marginal
marginal exposes four MCP tools that map cleanly to the testing loop. Your AI agent calls them in sequence to design and run an experiment.
A typical subject line A/B test starts with variant ideas and ends with a data-backed recommendation, all without leaving your editor or agent runtime.
- generate_variants — draft multiple subject line candidates
- launch_test — send the variants and begin tracking
- get_results — pull opens, clicks, and within-test lift
- recommend_next — let the agent suggest the winning direction
Built for AI agent email marketing
Because marginal speaks the Model Context Protocol, AI agent email marketing becomes a native workflow rather than a custom integration project. The email MCP server connects to the agents and editors you already use.
Supported clients include Cursor, OpenAI Codex, Claude Desktop, Claude Code, Windsurf, Cline, Continue, and Zed. The endpoint at https://marginal.sh/mcp authenticates with a Bearer API key, and the free tier covers 100 experiments per month.
- Hosted at https://marginal.sh/mcp — nothing to self-host
- Bearer auth with a marg_live_ key
- Free tier: 100 experiments/month
- Docs and tool references 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