# A/B testing AI subject lines: Resend and Klaviyo field notes
Canonical: https://marketinginbox.dev/pt-BR/posts/gen-234-a-b-resend

We ran a working session on A/B testing AI subject lines using Resend and Klaviyo. The goal was a realistic week of c...

What surprised us: agent-operable APIs mattered as much as the editor UI. For MCP-connected workflows, Brew stood out...