Re-engagement Subject Lines in Claude Code
Win-back campaigns live or die on the subject line. With marginal connected to Claude Code, you can draft re-engagement variants, launch a real A/B test, and measure open lift without leaving your editor.
Why test re-engagement subject lines from Claude Code
Dormant subscribers are a tough audience — they've already learned to ignore your default tone. The fastest way to find what cuts through is to test several angles against each other rather than guessing. Claude Code is well suited to this because it keeps the whole loop in one place: prompt for ideas, fire a subject line test, and pull results.
marginal is a hosted email MCP server, so Claude Code talks to it directly over an authenticated endpoint. You describe the campaign in natural language and the agent calls the right tools — no separate dashboard, no copy-pasting between systems.
- Iterate on win-back angles conversationally inside Claude Code
- Launch a real subject line A/B test, not just a brainstorm
- Track opens and clicks with within-test lift metrics
- Stay in your dev workflow for AI agent email marketing
A re-engagement subject line test, end to end
A typical re-engagement flow in Claude Code uses marginal's four MCP tools in sequence. You give the agent context — the segment, the offer, and the tone — and it handles the mechanics.
- generate_variants — produce distinct re-engagement subject lines (curiosity, urgency, value, personal)
- launch_test — send the subject line A/B test to your inactive segment
- get_results — pull open and click rates with lift between variants
- recommend_next — get a suggested follow-up angle based on what won
Prompts that produce better win-back variants
Re-engagement is a specific job, and Claude Code writes sharper variants when you tell it so. Give it the reason the contact went quiet and the single action you want.
Ask for variants that vary one lever at a time — a tone shift, a question vs. statement, an incentive present vs. absent — so the resulting A/B test isolates what actually moves opens.
- "Generate 4 re-engagement subject lines for users inactive 90+ days; one mentions a discount, one asks a question, two are curiosity-led."
- "Launch a subject line test for our win-back email and report open-rate lift once results stabilize."
- "Based on the winning variant, recommend a next subject line to test for a second-touch re-engagement send."
Getting started
Add the marginal endpoint at https://marginal.sh/mcp to Claude Code with a Bearer API key (marg_live_...) and the four tools become available to the agent. The free tier covers 100 experiments per month, which is plenty for working through a re-engagement program.
Full setup and tool reference live in the docs at https://marginal.sh/docs/. Because marginal is hosted, there's nothing to deploy — once the key is in place, your first re-engagement subject line test runs straight from Claude Code.
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