Testing Loyalty Reward Subject Lines in Windsurf
Loyalty reward emails live or die on the subject line. With marginal's email MCP server connected to Windsurf, you can generate, launch, and measure loyalty reward subject lines without leaving your editor — letting your AI agent handle the busywork while you watch the lift numbers.
Why loyalty reward emails need a subject line test
Reward emails carry high intent but compete with every other 'you've earned points' message in the inbox. Small wording changes — naming the reward amount, adding urgency, or leading with the member's tier — can swing opens meaningfully.
A structured subject line A/B test removes the guesswork. Instead of debating which phrasing feels best, you let real opens and clicks decide, then reuse the winning angle across your loyalty program.
- Lead with the concrete reward ('Your $15 reward is waiting')
- Test urgency vs. exclusivity framing
- Compare named-tier vs. generic greetings
- Measure within-test lift, not vanity averages
How the workflow runs inside Windsurf
Once marginal is configured as an MCP server in Windsurf, your AI agent can call the same four tools you'd use manually. Ask it to draft loyalty reward subject lines and it calls generate_variants; approve them and it calls launch_test against your list.
After the send, get_results returns open and click metrics with within-test lift so you can see which variant pulled ahead. recommend_next suggests the follow-up angle to try, keeping the loop tight.
- generate_variants — draft loyalty reward subject lines
- launch_test — start the managed send and subject line A/B test
- get_results — open/click tracking and lift metrics
- recommend_next — propose the next variant to try
A practical loyalty reward test prompt
In Windsurf, describe the campaign in plain language and let the agent orchestrate the tools. A good prompt names the reward, the audience, and the metric you care about.
For example: 'Generate five loyalty reward subject lines for members who just hit Gold tier, launch an A/B test to that segment, and report opens and click lift once results stabilize.' The agent handles variant generation, the managed send, and tracking through marginal.
- Specify the reward value and member tier for relevance
- Set a clear winning metric (opens or clicks)
- Let the agent run AI agent email marketing end to end
- Iterate with recommend_next for the next loyalty send
Getting started with marginal and Windsurf
marginal is a hosted email MCP server — there's nothing to self-host. Add the endpoint at https://marginal.sh/mcp with your Bearer API key (marg_live_...), and Windsurf can reach the generate, launch, results, and recommend tools immediately.
The free tier includes 100 experiments per month, enough to run several rounds of loyalty reward subject line tests. See https://marginal.sh/docs/ for setup details and tool references.
- Endpoint: https://marginal.sh/mcp
- Auth: Bearer API key (marg_live_...)
- Free tier: 100 experiments/month
- Works in Windsurf, Cursor, Claude, 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