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A field guide to the /form-email skill

AI HTML Email Template Design

Email clients break modern CSS. /form-email designs templates that render across Gmail, Outlook, and Apple Mail with mobile responsiveness in mind.

Form · Visual Design6 min readDecember 24, 2025

Email is the most hostile rendering environment in software. Outlook ignores half the CSS specification. Gmail strips classes. Apple Mail and Outlook for Mac mostly behave but still surprise. The design that looks great in a browser breaks in three of the top six email clients.

The /form-email skill designs HTML email templates calibrated to email-client constraints. Welcome sequences, transactional notifications, newsletters, drip campaigns. Layout with table-based fallback for legacy clients. Content blocks with proper image handling. CTA placement. Mobile responsiveness given the limited CSS support.

Tonone's /form-email skill designs HTML email templates that render across Gmail, Outlook, and Apple Mail with mobile responsiveness.

Install

/form-email ships with the Form agent in Tonone for Claude Code.

1. Add to marketplace

$ claude plugin marketplace add tonone-ai/tonone

2. Install Form

$ claude plugin install form@tonone-ai

Frequently asked questions

What does /form-email do?
It designs HTML email templates for welcome, transactional, newsletter, and drip campaigns calibrated to email client constraints.
How do I install /form-email?
Install Tonone for Claude Code via tonone.ai/get-started.

Pairs well with