Test Back in Stock Subject Lines in Cursor
Restock emails convert because they hit a customer who already wanted the item — but only if the subject line earns the open. With marginal connected to Cursor, you can generate, launch, and measure back in stock subject line tests without leaving your editor.
Why pair Cursor with marginal for restock emails
Cursor is where you already build product flows and trigger logic. marginal is a hosted email MCP server that adds four tools — generate_variants, launch_test, get_results, and recommend_next — so the AI agent in Cursor can run a full subject line A/B test against your back in stock campaign.
Because marginal is hosted, there's nothing to deploy. You point Cursor at the endpoint, authenticate, and ask the agent to spin up a test.
- Generate restock subject line variants from a single prompt
- Launch managed sends without a separate dashboard
- Track opens and clicks with within-test lift metrics
- Free tier covers 100 experiments per month
Writing back in stock variants that get opened
Back in stock messages have a built-in advantage: intent. The job of the subject line is to surface urgency and specificity. Ask the agent in Cursor to use generate_variants with the product name, scarcity signal, and tone you want to compare.
Good restock subject line tests usually pit different psychological angles against each other rather than tweaking single words.
- Urgency: "It's back — and going fast"
- Specificity: "The [Product] you wanted is in stock"
- Personalization: "You waited — it's here"
- Scarcity: "Only a few left of [Product]"
Running the subject line A/B test
Once you have variants, have the agent call launch_test to send them across your audience split. marginal handles the managed send and starts tracking opens and clicks immediately. From Cursor you can poll get_results to watch within-test lift accumulate.
When the test has enough signal, recommend_next tells you which back in stock subject line is winning and what to try next — so your AI agent email marketing loop keeps improving instead of guessing.
- launch_test — split your restock audience and send
- get_results — open/click rates and lift per variant
- recommend_next — winner plus the next variant idea
Getting connected
Add marginal to Cursor's MCP configuration using the endpoint https://marginal.sh/mcp and a Bearer API key in the marg_live_ format. From there the agent can drive your entire back in stock subject line test conversationally.
See the docs at https://marginal.sh/docs/ for the full tool reference and setup steps.
- Endpoint: https://marginal.sh/mcp
- Registry: sh.marginal/mcp
- Auth: Bearer API key (marg_live_...)
- Works in Cursor, Claude Code, Windsurf, Cline, and more
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