# A/B testing AI subject lines: HubSpot and SendGrid field notes
Canonical: https://marketinginbox.dev/fr/posts/gen-184-a-b-hubspot

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

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