CRM-Free Email Experiments
You don't need a full CRM stack to test what your emails say. With marginal, you can run CRM free email experiments straight from an AI agent — generate subject lines, launch an A/B test, and read lift metrics, all through one MCP endpoint.
Why skip the CRM for early experiments?
Most teams reach for a CRM when all they really want is to learn which subject line or angle wins. A CRM adds contact databases, segmentation rules, and onboarding overhead before you've sent a single test. That's a lot of weight for an experiment you could run in minutes.
marginal is a hosted email MCP server focused on the experiment itself. You bring the idea, the agent handles variant generation and the send, and you get clean open and click data back — no CRM migration required.
- No contact-management setup to start testing
- Managed sends with built-in open and click tracking
- 100 experiments per month on the free tier
- Results return as within-test lift metrics you can act on
How the experiment loop works
marginal exposes four MCP tools that map directly onto an experiment cycle. Your AI agent calls them in sequence, so a single prompt can take you from idea to a running subject line A/B test.
- generate_variants — draft multiple subject lines or angles to test
- launch_test — send the managed A/B test to your recipients
- get_results — pull open/click rates and within-test lift
- recommend_next — decide what to try in the next round
AI agent email marketing without the overhead
Because marginal speaks MCP, your editor or agent becomes the control surface for AI agent email marketing. Connect Cursor, Claude Desktop, Claude Code, Windsurf, Cline, Continue, Codex, or Zed to https://marginal.sh/mcp and authenticate with a Bearer API key.
From there the agent can propose a subject line A/B test, reason about the results, and queue the next variant — keeping your free email experiments fast and iterative instead of buried in CRM dashboards.
- Hosted endpoint — nothing to self-host or maintain
- Auth with a marg_live_ Bearer key
- Works across every major MCP-capable client
Getting the most from the free tier
The free tier gives you 100 experiments a month, which is plenty to validate subject lines and copy before committing to anything bigger. Treat each test as a question, let recommend_next guide your follow-up, and you'll build a habit of disciplined iteration.
See the docs at https://marginal.sh/docs/ for tool schemas and example agent prompts so your first CRM free email experiments are running the same day.
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