A No-Code ESP Alternative Built for Developers
Traditional email service providers assume you want a visual campaign builder. If you'd rather write a prompt and let an agent handle the rest, marginal is a no-code ESP alternative for developers that runs entirely through an email MCP server.
Why the no-code dashboard doesn't fit your workflow
Most ESPs sell a no-code experience as a feature: point-and-click templates, manual segment toggles, and a results screen you check by hand. For developers, that's friction in disguise. You context-switch out of your editor, click through a wizard, and copy numbers back into a spreadsheet.
marginal flips that model. Instead of a UI you operate, you get an MCP endpoint your AI agent calls. The same coding assistant you already use becomes the interface for generating variants, launching sends, and reading lift — no separate marketing console required.
- No drag-and-drop builder to learn or maintain
- Runs from Cursor, Claude Code, Windsurf, and other MCP clients
- Hosted at https://marginal.sh/mcp — nothing to self-host
- Authenticate with a single Bearer API key (marg_live_...)
Run a subject line A/B test from your agent
The core loop is built around testing. Ask your agent to draft subject line options, ship them to a real audience, and report back which one won — all through four MCP tools.
A typical subject line A/B test goes from idea to live send in one conversation, with open and click tracking plus within-test lift metrics so you know the result is the experiment, not noise.
- generate_variants — produce candidate subject lines
- launch_test — send the managed A/B test to your list
- get_results — pull opens, clicks, and lift per variant
- recommend_next — get the suggested follow-up based on data
AI agent email marketing without the glue code
Because marginal speaks the Model Context Protocol, AI agent email marketing stops being a stack of webhooks and SDK calls you wire together yourself. The agent discovers the tools, calls them with structured arguments, and handles the send and tracking lifecycle on marginal's hosted infrastructure.
That makes marginal a genuine alternative to a no-code ESP rather than a thin wrapper around one. Your agent does the orchestration; marginal does the delivery, measurement, and statistical comparison.
Start free and scale your experiments
The free tier includes 100 experiments per month, which is plenty to validate the workflow before committing. Point your MCP client at the marginal endpoint, add your API key, and start testing.
Read the setup details in the docs at https://marginal.sh/docs/ to connect your editor and run your first subject line A/B test.
- 100 experiments/month on the free tier
- Registry: sh.marginal/mcp
- Docs: https://marginal.sh/docs/
- Works across Codex, Claude Desktop, Cline, Continue, and Zed
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