# marginal.sh

> Hosted email marketing MCP server for AI agents.

marginal lets AI agents in Cursor, Codex, Claude Desktop, and other MCP clients run email marketing workflows: write subject lines, send split tests, track opens and clicks, and read experiment results. No ESP integration required — connect with only a marginal API key.

## Product

- Site: https://marginal.sh
- Docs: https://marginal.sh/docs/
- Privacy: https://marginal.sh/privacy.html
- MCP endpoint: https://marginal.sh/mcp
- MCP Registry ID: sh.marginal/mcp
- Registry listing: https://registry.modelcontextprotocol.io/v0.1/servers?search=sh.marginal/mcp

## Connect

1. Sign up at https://marginal.sh/signup
2. Create an API key at https://marginal.sh/dashboard
3. Add remote MCP server:

**Cursor / Claude Desktop**

```json
{
  "mcpServers": {
    "marginal": {
      "url": "https://marginal.sh/mcp",
      "headers": {
        "Authorization": "Bearer marg_live_..."
      }
    }
  }
}
```

**OpenAI Codex** (`~/.codex/config.toml` or `codex mcp add`)

```bash
export MARGINAL_API_KEY=marg_live_...
codex mcp add marginal --url https://marginal.sh/mcp --bearer-token-env-var MARGINAL_API_KEY
```

Docs: https://marginal.sh/docs/#codex

Optional CLI: `npx marginal-cli` (npm package: marginal-cli)

## MCP tools

| Tool | Purpose | Docs |
|------|---------|------|
| generate_variants | Subject lines from a brief, seed text, or agent-provided lines | https://marginal.sh/docs/tools/generate-variants.html |
| launch_test | Random split send to a recipient list with tracking | https://marginal.sh/docs/tools/launch-test.html |
| get_results | Per-variant opens, clicks, winner, within-test lift | https://marginal.sh/docs/tools/get-results.html |
| recommend_next | Suggestion for the next messaging angle to test | https://marginal.sh/docs/tools/recommend-next.html |

Agent workflow: https://marginal.sh/docs/#workflow

## Free tier

- 100 experiments / month
- 250,000 recipients / month
- 10 API keys
- No credit card at signup

## Contact

- Email: admin@marginal.sh

## Optional

- Sitemap: https://marginal.sh/sitemap.xml

## Guides

- Index: https://marginal.sh/guides/ (1106 long-tail pages, 1106 Opus-written)
- Examples: https://marginal.sh/guides/email-mcp-server.html, https://marginal.sh/guides/cursor-email-mcp-server.html, https://marginal.sh/guides/cart-abandonment-email-subject-line-test.html
- Regenerate copy: `npm run seo:write-content` (uses claude-opus-4-8)