Testing Review Request Subject Lines in Windsurf
Review request emails live or die by the subject line. With marginal connected as an email MCP server, you can draft, launch, and measure subject line A/B tests for your review requests directly inside Windsurf — letting the AI agent handle the busywork while you focus on the wording.
Why test review request subject lines
A review request is a low-friction ask, but the open rate determines whether anyone ever sees that ask. Small wording shifts — using a first name, naming the product purchased, or leading with gratitude versus a direct prompt — can move opens meaningfully. Guessing which one wins wastes sends.
Running a subject line test removes the guesswork. marginal measures within-test lift so you know whether a variant genuinely outperforms control rather than reading noise.
- Compare personalized vs. generic openers for review requests
- Test urgency ("Got 30 seconds?") against appreciation framing
- Measure open and click tracking on the review link itself
- Let lift metrics decide the winner, not gut feel
Connecting marginal in Windsurf
marginal is a hosted MCP server, so there's nothing to deploy. Add it to Windsurf's MCP configuration with your Bearer API key and point at the endpoint. Once connected, the four tools — generate_variants, launch_test, get_results, and recommend_next — become available to the AI agent in your Windsurf workspace.
Because the server is hosted at https://marginal.sh/mcp, you only need the endpoint and your key. No separate sending infrastructure or self-hosting is required.
- Registry: sh.marginal/mcp
- Endpoint: https://marginal.sh/mcp
- Auth: Bearer API key (marg_live_...)
- Docs: https://marginal.sh/docs/
{
"mcpServers": {
"marginal": {
"serverUrl": "https://marginal.sh/mcp",
"headers": {
"Authorization": "Bearer marg_live_your_key_here"
}
}
}
}A review request workflow in Windsurf
Prompt the AI agent in Windsurf to draft review request subject line variants, then launch them as a single managed test. marginal sends, tracks opens and clicks, and reports lift — the whole loop happens through the MCP tools without leaving your editor.
- Ask Windsurf to call generate_variants for 4–5 review request subject lines
- Use launch_test to split the send across your recipient list
- Pull get_results to see opens, clicks, and within-test lift
- Call recommend_next to surface the strongest direction for your follow-up
Tips for sharper variants
AI agent email marketing works best when the prompt is specific. Tell Windsurf the product category, the timing (days after delivery), and the tone you want so generated subject lines stay on-brand for review requests.
- Keep one strong control and vary a single lever per variant
- Reference the purchased item to lift relevance and opens
- Avoid over-testing — the free tier covers 100 experiments/month
- Re-run a subject line A/B test seasonally as buyer language shifts
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