Trial Conversion Subject Line Tests in Continue
Turn trial users into paying customers by testing the subject lines that get your nudge emails opened. With marginal's email MCP server connected to Continue, you can generate, launch, and measure trial conversion subject lines without leaving your editor.
Why test subject lines for trial conversion
Trial conversion emails — the day-3 check-in, the expiry warning, the feature-unlock nudge — only work if they get opened. The subject line is the single biggest lever on that open rate, and small wording changes can swing conversion meaningfully across a cohort.
Instead of guessing, a subject line A/B test lets you measure which framing actually moves trial users to come back and finish setup. marginal handles the experiment plumbing so you can focus on the message.
- Urgency vs. value framing for expiry reminders
- Personalized vs. generic openers for re-engagement
- Question vs. statement formats for feature nudges
- Within-test lift metrics so you know the winner is real
Using Continue with marginal
Continue is an open-source AI coding assistant, and once it's connected to marginal it can call email tools directly from chat. You describe the trial conversion campaign in natural language, and the agent drives the workflow through marginal's MCP tools.
marginal is a hosted email MCP server, so there's nothing to self-host. You authenticate with a Bearer API key (marg_live_...) and point Continue at the https://marginal.sh/mcp endpoint. From there, AI agent email marketing happens inside your normal dev loop.
- generate_variants — draft trial conversion subject lines
- launch_test — start a subject line A/B test on your list
- get_results — pull open and click tracking with lift
- recommend_next — get a data-backed next step
A trial conversion subject line workflow
Here's a typical loop you'd run from Continue. Each step maps to a marginal tool, so the agent can chain them in a single conversation.
Because results include within-test lift metrics, you don't have to eyeball raw open counts — recommend_next will surface whether a variant is a clear winner or whether you need more sends.
- Ask Continue to generate 4 subject line variants for an expiring-trial email
- Launch the subject line test against your trial cohort
- Let sends and open/click tracking run, then get_results
- Use recommend_next to ship the winner or iterate on framing
Getting started
The free tier includes 100 experiments per month, which is plenty to validate your core trial conversion sequence before scaling. Connect Continue to the marginal endpoint, run your first subject line test, and let the data pick the line that converts.
Full setup details and tool schemas live in the docs at https://marginal.sh/docs/, and the MCP endpoint is https://marginal.sh/mcp.
- Endpoint: https://marginal.sh/mcp
- Auth: Bearer API key (marg_live_...)
- Free tier: 100 experiments/month
- Docs: https://marginal.sh/docs/
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