Trial Conversion Subject Line Tests in Zed
Zed's AI assistant can drive your whole trial-to-paid email workflow when you connect it to marginal. This guide shows how to test trial conversion subject lines in Zed — generating variants, launching a managed send, and reading lift metrics — all from the editor you already write code in.
Why test trial conversion subject lines from Zed
Trial conversion is one of the highest-leverage email moments you own. A few percentage points of open-rate improvement on a day-3 or day-10 nudge can move real revenue, and the subject line is the first lever worth testing.
Because marginal exposes its tools over MCP, you can keep that experimentation next to your product code in Zed. Ask the agent to draft variants for a 'last day of trial' email, launch the subject line A/B test, and check back later — no context switch to a separate marketing dashboard.
- Stay in Zed where you're already shipping product changes
- Pair copy iterations with the feature changes that prompted them
- Let the AI agent handle the email marketing busywork end to end
Connect marginal as an email MCP server
marginal is a hosted email MCP server, so there's nothing to deploy. Point Zed at the endpoint and authenticate with your Bearer API key, then the four tools become available to the assistant.
Add the configuration below to Zed's MCP settings, using your live key (it starts with marg_live_).
- Endpoint: https://marginal.sh/mcp
- Auth: Bearer API key (marg_live_...)
- Tools: generate_variants, launch_test, get_results, recommend_next
- Free tier covers 100 experiments/month for early trial-conversion tests
A trial conversion subject line test, step by step
Once connected, describe the goal in plain language and let Zed's agent orchestrate the tools. A typical trial conversion run looks like this:
- Call generate_variants with your audience and a brief like 'urgency-driven subject for day 13 of a 14-day trial'
- Review the candidate subject lines and pick the ones worth running
- Use launch_test to send the subject line A/B test to your trial cohort with managed delivery
- Pull get_results for open/click tracking and within-test lift metrics
- Run recommend_next to let marginal suggest the follow-up variant to try
Reading lift and iterating
marginal reports open and click tracking plus within-test lift, so you can see how each subject line performed against the control rather than guessing from raw counts. That makes it easy to decide whether a winning line is worth promoting to your standard trial sequence.
Treat AI agent email marketing as a loop: ship a product change, ask Zed to spin up a fresh subject line test for the affected cohort, and feed the lift data back into your next message. Full tool reference and examples live in the docs at https://marginal.sh/docs/ and the endpoint is https://marginal.sh/mcp.
- Compare variants on lift, not just opens
- Promote winners into your evergreen trial flow
- Re-test when pricing, onboarding, or trial length changes
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