Streamable HTTP Email MCP for AI Agents
marginal is a hosted email MCP server that speaks Streamable HTTP, so your AI agent connects to one endpoint, authenticates with a Bearer key, and starts running subject line A/B tests immediately.
What Streamable HTTP means for email MCP
Streamable HTTP is the modern MCP transport that replaces the older SSE setup with a single endpoint capable of both request/response and streamed messages. For a Streamable HTTP email MCP like marginal, that means no local process to manage and no stdio bridge — your agent talks to https://marginal.sh/mcp directly over HTTPS.
Because marginal is hosted, there's nothing to self-host. You point a compatible client at the endpoint, pass your API key, and the email MCP server handles variant generation, sends, and tracking on the backend.
- Single endpoint: https://marginal.sh/mcp
- Auth via Bearer API key (marg_live_...)
- No self-hosted server or local daemon required
- Works with any client that supports Streamable HTTP MCP
Running a subject line A/B test over the wire
Once connected, the agent has four tools to drive a full experiment loop. A typical subject line A/B test starts with generating candidate lines, launching them to a split of your audience, then reading back lift metrics to pick a winner.
Every call goes through the same Streamable HTTP transport, so an AI agent doing email marketing can chain these tools in one session without juggling separate connections.
- generate_variants — draft subject line candidates
- launch_test — start a managed split send
- get_results — pull open/click and within-test lift
- recommend_next — get the suggested follow-up action
Connecting your client
marginal works with Streamable HTTP-capable MCP clients including Cursor, OpenAI Codex, Claude Desktop, Claude Code, Windsurf, Cline, Continue, and Zed. Each client points to the same registry entry, sh.marginal/mcp, and the same endpoint.
Configuration is just the URL plus your Bearer key. The free tier includes 100 experiments per month, which is plenty for validating a subject-line workflow before scaling up.
- Registry: sh.marginal/mcp
- Endpoint: https://marginal.sh/mcp
- Free tier: 100 experiments/month
- Docs: https://marginal.sh/docs/
Why agents prefer a hosted email MCP
Letting an AI agent run email marketing means giving it reliable, repeatable tools rather than brittle API glue. A Streamable HTTP email MCP keeps that surface small: one connection, typed tools, and structured results the agent can reason over.
marginal manages the sends and tracking itself, so the agent focuses on decisions — which variants to test, when to stop, and what to send next — instead of plumbing.
- Structured lift metrics agents can act on
- Managed sends with open/click tracking built in
- Consistent tool contract across every supported client
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