Loyalty Reward Subject Lines in Claude Code
Loyalty emails live or die on the subject line. With marginal connected to Claude Code, you can draft loyalty reward subject lines, run a subject line A/B test, and pull results — all from the same conversation where you write the rest of your code.
Why test loyalty reward subject lines from Claude Code
Loyalty reward campaigns reach people who already trust your brand, so the subject line has to feel earned rather than salesy. Small wording shifts — 'Your points are ready' versus 'A reward picked just for you' — can swing open rates meaningfully. Testing those variants is the only reliable way to know which framing your members respond to.
Claude Code is where many growth engineers already work, so wiring marginal in as an email MCP server keeps the loop tight. You describe the reward and audience, the agent generates subject line candidates, launches the test, and reports back — no context switching to a separate dashboard.
- Reward-tier framing: points balance, exclusive perk, or anniversary gift
- Urgency vs. appreciation tone for returning customers
- Personalization cues like member name or earned status
The MCP tools behind the workflow
marginal exposes four tools to your AI agent. For a loyalty reward subject line test you'll touch all of them in sequence, and Claude Code can chain the calls for you based on a plain-language prompt.
- generate_variants — produce loyalty-themed subject line options from your brief
- launch_test — start a subject line A/B test with a managed send
- get_results — pull open and click tracking plus within-test lift
- recommend_next — get a data-backed suggestion for the follow-up send
A practical run-through
Start by telling Claude Code the campaign details: the reward, the loyalty segment, and the tone you want. Ask it to generate five subject line variants, then launch a split test to your member list. Once enough sends accumulate, request results and let marginal report which variant earned the higher open rate and by how much.
Because marginal is hosted, there's nothing to deploy and no self-hosted server to maintain. You authenticate with a Bearer API key and the agent talks to the endpoint at https://marginal.sh/mcp directly.
- Prompt: 'Generate loyalty reward subject lines for members who hit Gold tier this month.'
- Prompt: 'Launch an A/B test of the top three and send to my loyalty segment.'
- Prompt: 'Show me the lift so far and recommend the next subject line.'
Getting set up
Add marginal to Claude Code's MCP configuration using your marg_live_ API key, then start prompting. The free tier covers 100 experiments per month, which is plenty to validate a loyalty reward subject line strategy before scaling. Configuration steps and tool references live in the docs at https://marginal.sh/docs/.
- Registry: sh.marginal/mcp
- Endpoint: https://marginal.sh/mcp
- Auth: Bearer API key (marg_live_...)
- Also works in Cursor, Claude Desktop, Windsurf, Cline, Continue, Zed, and OpenAI Codex
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