marginal MCP Pricing and the Free Tier
Looking into the marginal MCP pricing free tier before you wire up an agent? Here's exactly what you get without paying: 100 experiments per month against a hosted email MCP server, with subject line A/B testing and managed sends included.
What the free tier includes
marginal is a hosted email marketing MCP server, so there's nothing to deploy or maintain. The free tier gives you 100 experiments per month — enough to evaluate whether agent-driven subject line testing fits your workflow before committing to anything larger.
- 100 experiments/month at no cost
- Full access to all four MCP tools: generate_variants, launch_test, get_results, recommend_next
- Subject line A/B test orchestration with open and click tracking
- Within-test lift metrics so you can see which variant won
- Bearer API key auth (marg_live_...) — no infrastructure to run
How an experiment is counted
An experiment is a single subject line A/B test you launch and measure. When your AI agent calls launch_test, that consumes one of your monthly experiments. Generating variants and reading results don't burn additional experiments — only the launch does.
This makes the free tier predictable for prototyping. A growth engineer can let an agent run a handful of tests per week, review the within-test lift, and iterate without watching a meter.
Connecting your agent
The free tier works with every supported MCP client, so AI agent email marketing setups can start immediately. Point your client at the endpoint https://marginal.sh/mcp and authenticate with your Bearer API key.
- Compatible clients: Cursor, OpenAI Codex, Claude Desktop, Claude Code, Windsurf, Cline, Continue, Zed
- Endpoint: https://marginal.sh/mcp
- Registry name: sh.marginal/mcp
- Setup details live in the docs at https://marginal.sh/docs/
When to look past the free tier
The 100 experiments/month allowance covers evaluation and light production use. If your agent runs frequent campaigns and you need more headroom, you'll want a higher capacity than the free tier provides. Until then, you get the same email MCP server, the same tools, and the same managed sends — just metered to 100 experiments a month.
Because marginal is fully hosted, scaling up is purely a question of capacity, not configuration. Your subject line A/B test flows, tracking, and lift metrics stay identical whether you're on the free tier or beyond it.
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