Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx skills add hoangatg/ai-agent-toolkit --skill email-developmentgit clone --depth 1 https://github.com/hoangatg/ai-agent-toolkitWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/hoangatg/ai-agent-toolkit/email-development)<a href="https://agentmods.dev/skills/hoangatg/ai-agent-toolkit/email-development"><img src="https://agentmods.dev/badge/skills/hoangatg/ai-agent-toolkit/email-development/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/skills/hoangatg/ai-agent-toolkit/email-development"><img src="https://agentmods.dev/badge/skills/hoangatg/ai-agent-toolkit/email-development.svg" alt="Reviewed on agentmods" width="80" height="20"></a>What it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00030 | $0.00859 |
| Opus 5 | $0.00015 | $0.00430 |
| Sonnet 5 | $0.00006 | $0.00172 |
| Haiku 4.5 | $0.00003 | $0.00086 |
Grade A, and why
email-development scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 8d ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
How it starts
The opening of the file, as written. The whole thing — 129 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Email Development
The most universal communication channel — and the hardest to style.
1. Email Types
| Type | Purpose | Tool |
|---|---|---|
| Transactional | Receipts, password reset, notifications | SendGrid, Resend, AWS SES |
| Marketing | Newsletters, promotions, drip campaigns | Mailchimp, ConvertKit |
| Automated | Welcome series, abandoned cart | Customer.io, Braze |
2. HTML Email Development
Key Constraints
| Constraint | Why |
|---|---|
| Table-based layout | Outlook doesn't support flexbox/grid |
| Inline styles | Many clients strip <style> tags |
| No JavaScript | Completely stripped |
| Limited CSS | No media queries in many clients |
| Image blocking | Many clients block images by default |
Modern Tools
| Tool | Purpose |
|---|---|
| React Email | React components → HTML email |
| MJML | Responsive email framework |
| Maizzle | Tailwind CSS for email |
| Litmus/Email on Acid | Cross-client testing |
| Resend | Modern email API |
3. Responsive Design
Strategy
| Approach | Support |
|---|---|
| Fluid layout | width: 100%; max-width: 600px |
| Hybrid/spongy | Works without media queries |
| Media queries | iOS Mail, Apple Mail, Gmail app |
Email Width Standards
| Element | Width |
|---|---|
| Max width | 600px |
| Content padding | 20px sides |
| CTA button | Min 44px height (touch target) |
| Font size | Min 14px body, 22px+ heading |
4. Deliverability
Authentication
| Protocol | Purpose |
|---|---|
| SPF | Authorize sending servers |
| DKIM | Sign emails cryptographically |
| DMARC | Policy for failed auth |
| BIMI | Brand logo in inbox |
Best Practices
| Practice | Impact |
|---|---|
| Clean list | Remove bounces, unsubscribes |
| Warm up IP | Gradual volume increase |
| Avoid spam triggers | No ALL CAPS, excessive links |
| Text version | Always include plain text |
| Unsubscribe | One-click, visible link |
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 8d ago First seen · 129 lines · 30 tokens per session scan A 0edf99e2c5ea
email-development is a skill published in the GitHub repository hoangatg/ai-agent-toolkit (1 stars, last pushed 5mo ago), licensed MIT. It adds 30 tokens to every session and 859 once invoked, about $0.0002 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-09-03.
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