Instant Email Campaign Launch API for AI Agents
If you want an instant email campaign launch API that an AI agent can call directly, marginal exposes campaign creation, subject line testing, and managed sends as MCP tools — so launching is one tool call away.
Launch in one call, not one workflow
Traditional email tooling makes "launch" a multi-step dance: build a template, configure an audience, schedule a send, then wire up tracking. An instant email campaign launch API collapses that into a single action your agent can trigger the moment it has a draft ready.
marginal's launch_test tool takes your variants and an audience and ships the send immediately, with open and click tracking attached automatically. There's no separate analytics setup — the test is live and measurable from the first send.
- generate_variants — produce subject line and copy options
- launch_test — ship the campaign as a managed send
- get_results — pull opens, clicks, and within-test lift
- recommend_next — get the agent's next-step suggestion
Subject line A/B testing without the overhead
Most instant launches skip experimentation because setting up a subject line A/B test is friction. marginal flips that: every launch is a test by default. You pass multiple subject lines, marginal splits the audience, and lift metrics come back through get_results.
That means your AI agent email marketing loop can launch fast and still learn from every send. No manual variant assignment, no spreadsheet to reconcile winners.
- Split audiences across subject line variants automatically
- Track opens and clicks per variant
- Read within-test lift to identify the strongest line
- Feed results back into the next generation of copy
Built as a hosted email MCP server
marginal is a hosted email MCP server — there's nothing to deploy or self-host. You point your MCP client at https://marginal.sh/mcp, authenticate with a Bearer API key (marg_live_...), and the launch tools are available to your agent immediately.
Because it speaks the Model Context Protocol, the same instant launch capability works across Cursor, Claude Desktop, Claude Code, Codex, Windsurf, Cline, Continue, and Zed without per-client glue code.
- Endpoint: https://marginal.sh/mcp
- Registry: sh.marginal/mcp
- Auth: Bearer API key (marg_live_...)
- Free tier: 100 experiments per month
A typical instant-launch loop
Here's how the pieces fit when an agent owns the campaign end to end. Each step is a single MCP tool call, so the entire cycle from idea to live send happens inside one agent run.
- Call generate_variants to draft subject line options
- Call launch_test to send and start the A/B test
- Poll get_results for opens, clicks, and lift
- Call recommend_next to decide the follow-up send
- See the full reference 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