Is hubspot-email safe to install?

SaferSkills independently audited hubspot-email (Agent Skill) and scored it 100/100 (green). The audit ran 55 deterministic rules across Security, Supply Chain, Maintenance, Transparency, and Community; it found 0 high-severity and 0 lower-severity findings. The full rule-by-rule trace and per-finding evidence are below. Free, methodology-open.

CategoryWeightCategory scoreContribution

Securityprompt, exec, net, exfil, eval

35%

100

35.0 pts

Supply chainhash, typosquat, maintainer, lockfile

20%

100

20.0 pts

Maintenancestaleness, pinning, CI

15%

100

15.0 pts

TransparencySKILL.md, perms, README

15%

100

15.0 pts

Communityinstalls, verify, response

15%

100

15.0 pts

Findings & checks · 0 flagged

Securityscore 100 · 0 findings

✓—All security checks passedNo findings in this category for the latest scan.pass

Supply chainscore 100 · 0 findings

✓—All supply chain checks passedNo findings in this category for the latest scan.pass

Maintenancescore 100 · 0 findings

✓—All maintenance checks passedNo findings in this category for the latest scan.pass

Transparencyscore 100 · 0 findings

✓—All transparency checks passedNo findings in this category for the latest scan.pass

Communityscore 100 · 0 findings

✓—All community checks passedNo findings in this category for the latest scan.pass

The primary manifest — the file an agent reads to learn what this artifact does.

.claude/skills/hubspot-email/SKILL.md · 1 file

.claude/skills/hubspot-email/SKILL.md46.2 KB · Markdown

name: hubspot-email

version: 1.1.0

description: "Build HTML email templates for HubSpot. Use when the user wants to create, edit, or troubleshoot HubSpot email templates. Also use when the user mentions 'HubSpot email,' 'email template,' 'HubL email,' or 'email HTML.' For email sequences and drip campaigns, see email-sequence. For CTA buttons, see hubspot-cta."

HubSpot Email Templates

You are an expert email developer creating HTML email templates for upload to HubSpot. Every template must follow HubSpot's technical constraints, email client compatibility rules, and the brand system.

Scope boundary — pull two `web-design` reference files for email. Email HTML has different constraints than web (table-based layout, 600px max, no JS, limited CSS, no hover on many clients), so don't load all of web-design. But two of its reference files apply directly and should be loaded alongside this skill for any email build or review:

.claude/skills/web-design/references/accessibility.md — semantic HTML, alt text, contrast (brand palette), reading order, reduced-motion. Email a11y matters and this covers the gaps brand-guide doesn't.
.claude/skills/web-design/references/anti-patterns.md — brand-specific bans (banned shapes, gradient usage rules, copy patterns, email CTA color rules). All apply to email.

Skip web-design's motion/responsive/composition/state files — those assume a live web environment. Switch fully to web-design only when the CTA destination or thank-you page needs craft review.

Before Building

Always read these first:

/brain/brand-guide/brand-guide.md — colors, typography, spacing, brand system
This skill file — HubSpot constraints and email HTML rules

If the email includes product claims or copy: Read /brain/truth.md and /brain/positioning-and-messaging.md to ensure accuracy. Never invent product facts.

Gather this context (ask if not provided):

1. Email Type

What kind of email? (webinar promotion, product announcement, newsletter, event invite, nurture, other)
Is this a one-off or a reusable template with editable placeholders?

2. Content

What is the primary message?
Any supporting content (bullets, speaker bios, dates, CTAs)?
How many CTAs? What action(s)?

3. Upload Method

AI Upload (paste HTML, HubSpot recreates in drag-and-drop) — more limitations
Coded Template (Design Manager, full HubL support) — more control
Default to AI Upload constraints (strictest) unless told otherwise

HubSpot AI Upload Limitations

When creating templates for HubSpot's "Upload external email template" feature, these elements will not transfer:

Limitation	Impact	Workaround
Max width 600px	Container must be 600px or narrower	Always use 600px container
No background gradients	CSS `linear-gradient` on backgrounds is stripped	Use solid background colors. Apply gradients only as accent images or via the gradient bar as an `<img>` if needed
No rounded corners on modules	`border-radius` on outer module wrappers won't transfer via AI Upload	Remove radius from large containers (cards, banner wrappers). Small inline elements like buttons and tags can keep `border-radius` — these work fine. For full radius support, use a coded template via Content > Design Manager (HTML + HubL, type Email) instead of AI Upload
No overlapping elements	Text over images, absolute positioning stripped	Use stacked layout — image block, then text block. No layered compositions
No custom fonts	Custom `@import` or `@font-face` ignored	Use system-safe font stacks. The brand font won't render — fall back to `Arial, Helvetica, sans-serif`
No custom modules	HubSpot-specific modules won't transfer	Use standard HTML tables and content blocks
Images must be publicly hosted	Local or private image URLs won't load	Use publicly accessible URLs (e.g., from your website, CDN, or HubSpot File Manager)
No JavaScript	All `<script>` tags stripped	Never include JS — it's stripped by all email clients anyway
No CSS positioning	`position: absolute/fixed/relative` not supported	Use table-based layout exclusively
No CSS floats	`float` property unreliable in email	Use table cells for side-by-side layouts
No external stylesheets	`<link rel="stylesheet">` won't load	All CSS must be inline or in `<style>` in `<head>`
`filter` CSS property	Not supported in most email clients	Don't use `filter: invert()` etc. — use pre-made white icon assets instead
Social module icons	Platform-specific social icons for some niche networks not supported	Use simple image icons with links

What DOES Transfer Well

Table-based layouts
Inline styles
Solid background colors
Standard images (publicly hosted)
Text formatting (bold, italic, size, color)
Links and buttons (with inline styles)
Basic <style> block in <head> (HubSpot inlines it)
Media queries in a separate <style> block (for responsive)

HubSpot Coded Template Requirements

When building templates for upload via Design Manager (coded templates), follow these requirements.

Template Annotations (Design Manager)

Every coded email template file must start with template annotations as an HTML comment before the DOCTYPE:

<!--
  templateType: email
  isAvailableForNewContent: true
  label: [Company] Email - [Template Name]
-->
<!DOCTYPE html>

templateType: email — tells Design Manager this is an email template
isAvailableForNewContent: true — makes it selectable when creating new emails
label — display name in the template picker

HubL Editable Fields

Use these HubL tags to create editable fields that appear in the email editor sidebar:

{# Editable text — use for short fields (titles, names, dates, URLs) #}
{% text "field_id" label="Field Label", value="Default value", no_wrapper=True %}

{# Editable rich text — use for paragraphs, formatted content #}
{% rich_text "field_id" label="Field Label", html="<p>Default content</p>", no_wrapper=True %}

{# Boolean toggle — use to show/hide sections #}
{% boolean "field_id" label="Show Section", value=True, export_to_template_context=True %}

{# Module — use for HubSpot-managed email modules #}
{% module "module_id" path="@hubspot/email_cta" %}

Important: Always use no_wrapper=True when placing {% text %} or {% rich_text %} inside styled containers. Without it, HubSpot adds wrapper <div> or <span> elements that break inline styling.

Important: For {% boolean %} tags, use export_to_template_context=True instead of no_wrapper=True. Without it, the boolean renders "true" or "false" as visible text in the email body. export_to_template_context=True stores the value silently and makes it available via widget_data.field_id.value.

Conditional sections with boolean:

{% boolean "show_section" label="Show Section", value=True, export_to_template_context=True %}
{% if widget_data.show_section.value %}
  <!-- HTML for the conditional section -->
{% endif %}

Email Template Validator — Rejected Patterns

HubSpot's email template validator rejects several patterns. Common ones:

{% dnd_area %} with any name other than "main"
a class attribute on {% dnd_area %}
{% text %} tags used as editable fields inside email module markup
module field names body (use body_text) and name (use something descriptive like event_name)

When HubSpot blocks a tag type for editable fields, wrap those fields in a micro custom module and include it via {% module "label" path="./modules/foo" %}.

Personalization Token — Greeting Pattern

When using a personalization token for greetings (e.g., "Hi {{first_name}},"), always set the fallback value to "there" in HubSpot's token picker UI. This produces:

With name: "Hi Rita,"
Without name: "Hi there,"

Do NOT leave the fallback blank or use a space. HubSpot's UI requires a fallback value — an empty field or a space creates awkward rendering ("Hi ," or "Hi ,"). The word "there" is the established pattern for all [Company] emails.

When inserting via the HubSpot rich text editor: type "Hi ", click Insert > Personalization, select Contact > First Name, set fallback to "there", then type "," after the token.

For the coded template equivalent:

Hi {% personalization_token "contact.firstname", "there" %},

Default Email Modules Reference

Email modules are different from web page modules. Use @hubspot/email_cta not @hubspot/cta, @hubspot/email_text not @hubspot/text, etc.

Module	Path	Use For
Call-to-Action	`@hubspot/email_cta`	HubSpot-managed CTA (renders its own markup)
Main Email Body	`@hubspot/email_body`	Primary email content (rich text)
Logo	`@hubspot/email_logo`	Company logo (pulls from account settings)
Image	`@hubspot/image_email`	Standalone image
Linked Image	`@hubspot/email_linked_image`	Image with link
Header	`@hubspot/email_header`	Heading (h1-h6)
Text	`@hubspot/email_text`	Single line of text
Section Header	`@hubspot/email_section_header`	Header + subheader
CAN-SPAM Footer	`@hubspot/email_can_spam`	Auto-populated business address + unsubscribe
Social Sharing	`@hubspot/email_social_sharing`	Social share buttons
Raw HTML	`@hubspot/raw_html_email`	Custom HTML block
Video	`@hubspot/video_email`	Video embed with thumbnail
Blog Post Filter	`@hubspot/email_post_filter`	Blog post filter by tag/author/month
Blog Post Listing	`@hubspot/email_post_listing`	Recent/popular blog posts
Subscriptions	`@hubspot/email_subscriptions`	Subscription preferences page
Subscription Confirmation	`@hubspot/email_subscriptions_confirmation`	Subscription change confirmation
Unsubscribe (Backup)	`@hubspot/email_simple_subscription`	Simple unsubscribe form

IMPORTANT: `@hubspot/rich_text_email` does NOT exist. There is no email-specific rich text module. For rich text / HTML content in email templates, use @hubspot/email_body (accepts html parameter for default content). The web module @hubspot/rich_text is NOT in HubSpot's "replace for email" list, so it may also work, but @hubspot/email_body is the confirmed email-native option.

CTA Buttons in Email Templates

IMPORTANT: `{% cta %}` does NOT work in HubSpot marketing emails. The {% cta %} HubL tag is for web/landing pages only. Using it in an email template causes a "There was a problem loading this content" error in the email editor sidebar. This was confirmed by HubSpot support.

#### Recommended Approach: @hubspot/email_cta Module

Use the native CTA module. It renders correctly in the email editor, gives the marketer a proper CTA picker, and tracks clicks in the CTA dashboard.

{% module "cta" path="@hubspot/email_cta", label="CTA Button" %}

Do NOT wrap this in a `<div>`. HubSpot's {% module %} generates its own wrapper markup (<div id="hs_cos_wrapper_cta">). Adding a parent div hides the module entirely in the email editor.

Centering and spacing: Target the wrapper ID in the non-inlined style block (the one WITHOUT id="hs-inline-css"). Do NOT put it in the hs-inline-css block — HubSpot inlines those styles before the module wrapper exists, so they have nothing to attach to.

<!-- Non-inlined styles — HubSpot keeps these as <style> in <head> -->
<style type="text/css">
  /* Center the CTA module wrapper and its inner table */
  #hs_cos_wrapper_cta { text-align: center; padding: 16px 24px 0 24px; }
  #hs_cos_wrapper_cta table { margin: 0 auto; }
</style>

Why this works: The non-inlined <style> block stays in the <head> as a CSS rule. At render time, the module wrapper exists and the rules apply. text-align: center centers inline content; margin: 0 auto on the inner table centers block-level content. Works in Gmail, Apple Mail, iOS, and most modern clients. Outlook may ignore the <style> block (button still renders, just left-aligned).

Brand colors: Marketer sets the CTA background, text color, and corner radius from brain/brand-guide/brand-guide.md in the CTA editor's Styles tab. Some brand accents render inconsistently across email clients — Outlook, dark-mode Gmail, and forwarded chains can shift saturated colors. The brand guide should name an email-safe CTA color; verify it in major clients before standardizing. Web-safe accents can stay the default on landing pages where contrast is reliable.

What you get: CTA dashboard tracking (views, clicks, conversions), native "Link to: CTA" picker, marketer controls styling via editor UI. What you don't get: Pixel-perfect brand CSS from the template — marketer sets brand colors manually per-email.

CTA card copy: headlines work better as imperatives that pair with the button ("See X in action" + "Book a demo") than as noun phrases ("X in action"). Flow: kicker poses the problem → imperative headline points to the solution → body proves it → button takes action. Avoid echo between the kicker, headline, and body opener — a headline that repeats the kicker's opening words is a dead giveaway.

#### Comparison

Approach	Brand Control	CTA Dashboard	Editor UX
`@hubspot/email_cta` module (recommended)	Marketer sets in Styles tab	Yes — views, clicks, conversions	Native CTA picker + style editor
~~Styled `<a>` + `{% text %}`~~	~~Full inline CSS~~	~~Per-email only~~	Breaks in Remix editor — HubSpot auto-converts to broken module
~~`{% cta %}` tag~~	~~N/A~~	~~N/A~~	Does not work in emails — page-only tag

Drag-and-Drop (dnd_area) Email Templates

HubSpot's email editor (Remix) always uses a drag-and-drop editor. Even coded templates get auto-converted to dnd modules — and the conversion often breaks (producing "Unknown Module" or uneditable modules). The fix: use {% dnd_area %} tags to control how HubSpot builds the module tree.

When to Use dnd_area

Choose between classic HubL and dnd_area based on who controls the layout.

Classic HubL ({% text %}, {% rich_text %}, {% boolean %}): template author locks the structure, marketers only fill in labelled fields. Use this for brand-critical recurring templates (newsletters, promos, announcements) where design consistency matters more than layout flexibility. Classic HubL templates render correctly in the Remix email editor.
dnd_area: template author provides a starter layout, marketers drag/drop/reorder modules per send. Use when different issues need different structures, or when multiple non-technical marketers need layout flexibility without touching code.

For a single-marketer workflow with tight design control ([Company] today), classic HubL is usually the right default. Reach for dnd_area when layout flexibility per send is more valuable than brand-lockdown consistency.

Required `<head>` Includes

{{ dnd_area_stylesheet }}   <!-- REQUIRED for dnd_area rendering -->
{{ email_header_includes }}  <!-- Cross-client rendering -->
{{ reset_css_stylesheet }}   <!-- Cross-client CSS reset -->

Constraints

Only ONE `dnd_area` per email template (HubSpot limit)
`dnd_row` is NOT supported in email — use dnd_section > dnd_column > dnd_module
Minimum width: 624px
Static HTML (logo, footer) goes OUTSIDE the dnd_area — locked, not editable per-email
Module defaults are passed as parameters in the dnd_module tag

Architecture Pattern

Static HTML (not editable)
├── Logo header
├── Gradient accent bar

{% dnd_area "main", full_width=False %}
├── dnd_section → dnd_column → dnd_module (content)
├── dnd_section → dnd_column → dnd_module (more content)
├── dnd_section → dnd_column → dnd_module @hubspot/email_cta
{% end_dnd_area %}

Static HTML (not editable)
├── Footer (logo, social, CAN-SPAM, unsubscribe)

Pre-place a starter layout. For recurring dnd_area newsletter templates, pre-place default {% dnd_module %} tags inside the dnd_area with realistic starter content (e.g. Featured + 2 Blog Posts + 1 Event + Dev Corner). This gives the marketer a working starting layout instead of an empty canvas.

Section markers on repeatable modules. For repeatable dnd custom modules (blog post, event, industry item), add a show_section_marker boolean field. Turn it ON for the first item in a group and OFF for the rest, so they stack cleanly under one marker and one leading divider. This prevents duplicate 'LATEST POSTS'-style headers when the marketer drops multiple instances.

Static-vs-dnd Horizontal Alignment Gotcha

The bug: In a template mixing a static masthead/footer with a dnd_area, the dnd module content renders ~10px to the right of the static sections — even when both use the same inner padding (e.g. padding: 0 40px). Visible as a misaligned divider/separator line or an off-axis share-row box.

Why it happens: HubSpot's dnd_area_stylesheet (injected via {{ dnd_area_stylesheet }}) adds default horizontal padding to the .dnd-section / .dnd-column / .dnd-module wrappers it generates. Those wrappers sit between your email-container <td> and your module's HTML, so the effective left offset of module content is (module inner padding) + (wrapper padding), while static masthead/footer content is just (td padding).

What does NOT fix it (tried and failed on a real newsletter build):

padding={'top':0,'bottom':0,'left':0,'right':0} on dnd_section / dnd_column
hs_wrapper_css={'padding':'0'} on every dnd_module
full_width=False on dnd_area and dnd_section (still a good idea for other reasons, but doesn't fix the offset)
A <style> block in the template <head> with !important overrides on .dnd-section / .dnd-column / .dnd-module — HubSpot's stylesheet injection wins the specificity war somehow.

What DOES fix it — adjust the static sections, not the dnd wrappers. Measure the offset live in devtools (in the company's case: ~10px), then bump the left (and usually right) padding on every static <td> by that amount so it aligns with the module content. The dnd wrapper's offset is fixed — you match it from the static side.

Concrete pattern that worked (modules use 40px inner L/R padding, wrapper adds ~10px each side):

<!-- Masthead: left 50 (not 40) to match dnd module content -->
<td style="padding: 48px 40px 32px 50px;">...masthead...</td>

<!-- Share row: 50 L and R so the box aligns with module content both sides -->
<td style="padding: 48px 50px 0 50px;"><div>...share box...</div></td>

<!-- Footer divider: 50 L and R so the line matches module dividers -->
<td style="padding: 32px 50px 0 50px;"><div style="border-top: 1px solid #E5E7EB;">&nbsp;</div></td>

Rule of thumb: don't fight HubSpot's dnd wrapper. Measure the offset once, then pad the static sections to match. This keeps all the module padding logic untouched and doesn't rely on CSS override tricks that don't actually work.

Diagnose 'shifted' or 'off' before fixing. When a user flags an email as 'shifted' or 'off,' identify the specific element first. 'Shifted right' can mean viewport-level centering (usually a client or editor-preview quirk, not a bug) or element-level misalignment between static and dnd sections (the real bug, above). Ask which — don't guess. The wrong assumption burns test-send round-trips.

Pre-placed vs. Dragged Module Width

Pre-placed {% dnd_module %} content is wrapped by HubSpot's editor with different default styles than modules the marketer drags in at runtime. If pre-placed content renders at a different width than dragged content, try hs_wrapper_css={'padding':'0'} on the {% dnd_module %}, or check whether the {% dnd_area %} needs full_width=False to stay inside its parent container's max-width.

Module Paths for dnd Email

Only use modules confirmed to work in dnd email context:

Module	Path	Works in dnd email
CTA Button	`@hubspot/email_cta`	Confirmed
Image	`@hubspot/image_email`	Confirmed (in official docs)
Email Body (rich text)	`@hubspot/email_body`	Testing
Raw HTML	`@hubspot/raw_html_email`	Testing
One line of text	`@hubspot/email_text`	Testing

Do NOT use `@hubspot/rich_text_email` — this path does not exist and produces "Unknown Module" errors.

Module folder convention. Place custom modules for a dnd_area template in a modules/ subfolder next to the template and reference them as dnd_module path="./modules/name". This mirrors the repo layout to the Design Manager folder structure and makes uploads predictable.

Syntax Examples

Rich text content with default HTML:

{# Example values — use the email background and body text colors from /brain/brand-guide/brand-guide.md #}
{% dnd_section
    background_color={'color':'#111111'},
    padding={'top':'0','bottom':'0','left':'24','right':'24'}
%}
  {% dnd_column width=12 %}
    {% dnd_module
        path='@hubspot/email_body',
        html='<div style="font-size: 16px; color: #FFFFFF;">Default content here</div>'
    %}
    {% end_dnd_module %}
  {% end_dnd_column %}
{% end_dnd_section %}

CTA button (native editor):

{# Example background — use the email background color from /brain/brand-guide/brand-guide.md #}
{% dnd_section
    background_color={'color':'#111111'},
    padding={'top':'36','bottom':'0','left':'24','right':'24'}
%}
  {% dnd_column width=12, horizontal_alignment='CENTER' %}
    {% dnd_module path='@hubspot/email_cta' %}
    {% end_dnd_module %}
  {% end_dnd_column %}
{% end_dnd_section %}

Marketer sets brand colors manually in Button module style tab: the brand guide's email CTA background, button text color, and corner radius.

Image module:

{% dnd_module path='@hubspot/image_email',
    img={'alt':'Logo', 'height':32, 'src':'https://example.com/logo.svg', 'width':143},
    alignment='center'
%}
{% end_dnd_module %}

dnd_section Parameters

{# Example background — use the card/surface color from /brain/brand-guide/brand-guide.md #}
{% dnd_section
    background_color={'color':'#111111'},
    padding={'top':'0','bottom':'0','left':'24','right':'24'},
    max_width=600
%}

{{ site_settings.company_name }}
{{ site_settings.company_street_address_1 }}
{{ site_settings.company_street_address_2 }}
{{ site_settings.company_city }}
{{ site_settings.company_state }}
{{ site_settings.company_zip }}
{{ site_settings.company_country }}

Required Links

<!-- Unsubscribe -->
<a data-unsubscribe="true" href="{{ unsubscribe_link }}">Unsubscribe</a>

<!-- Unsubscribe from all -->
<a data-unsubscribe="true" href="{{ unsubscribe_link_all }}">Unsubscribe from all</a>

<!-- View as webpage -->
<a data-viewaswebpage="true" href="{{ view_as_page_url }}">View as web page</a>

Preview Text

<div id="preview_text" style="display:none!important;">
  {% text "preview_text" label="Preview Text" value="Preview text here" %}
</div>

CSS Inlining

Use id="hs-inline-css" on style blocks that should be compiled to inline CSS:

<style type="text/css" id="hs-inline-css">
  /* These styles will be inlined on target elements */
  td { font-family: Arial, sans-serif; }
</style>

Keep media queries in a separate <style> block (without the inline ID) so they aren't inlined:

<style type="text/css">
  @media only screen and (max-width: 620px) {
    .mobile-full { width: 100% !important; }
  }
</style>

Email HTML Best Practices

Layout

Always use tables for layout. <table role="presentation"> with cellspacing="0" cellpadding="0" border="0"
600px max width for the email container
Single-column layouts are most reliable across clients
Stack on mobile: Multi-column desktop layouts should collapse to single column via media queries
Use align="center" on wrapper <td> to center the email container

CSS

Inline all critical styles. Email clients strip <style> blocks unpredictably
Keep a <style> block in <head> as progressive enhancement, but don't rely on it
Media queries go in their own <style> block
Never use: position, float, flexbox, grid, filter, clip-path, calc(), CSS variables
border-radius works in most clients except Outlook (degrades gracefully to square)
background-image unreliable in Outlook — always have a solid background-color fallback

Typography

Use system-safe font stacks: Arial, Helvetica, sans-serif or Georgia, serif
@import Google Fonts as progressive enhancement — they render in Apple Mail, iOS, some Android — but always include fallback
For AI Upload: don't rely on custom fonts at all
Minimum body text: 14px. Recommended: 16px for readability on mobile
Link colors on light backgrounds must pass WCAG AA (4.5:1). Many brand accents fail on white — define a darker, accessible variant of the accent for links on light backgrounds, and record it in the brand guide

Images

All images must be publicly accessible URLs
Always include alt text, width, height, and style="display: block; border: 0;"
Use width attribute (not just CSS) for Outlook compatibility
Don't use CSS filter on images — use pre-made assets in the correct color
Compress images for fast load times
60/40 rule: Approximately 60% text, 40% images for deliverability
Hugging the left edge: wrap an image inside a <td> in a zero-whitespace table (<td style="padding:0; line-height:0; font-size:0;">) when it must sit flush-left with other siblings. A plain <a><img></a> inside a <td> picks up a leading space from surrounding HTML whitespace in some clients, offsetting the image to the right of other left-aligned elements.

Icons

For newsletter and digest-style emails, use line icons (e.g. Lucide) paired with uppercase section labels rather than emoji. Emoji looks dated and can't match brand voice; line icons give a clean, modern, TLDR-like feel.

Icon workflow: download the Lucide SVG from unpkg.com/lucide-static@latest/icons/{name}.svg, bake the brand accent hex in place of currentColor with sed 's/stroke="currentColor"/stroke="#RRGGBB"/' (use the accent hex from the brand guide), then rasterize to a 40×40 PNG with rsvg-convert -w 40 -h 40. Store both the SVG and PNG side by side in marketing/icons/{category}/, and reference the PNG in email (SVG support is unreliable across clients).

Buttons

Use the bulletproof button pattern (table-based) for Outlook compatibility:

<!-- Placeholder colors — use the email CTA background and button text colors from the brand guide -->
<table role="presentation" cellspacing="0" cellpadding="0" border="0">
  <tr>
    <td style="background-color: #333333; border-radius: 12px; text-align: center;">
      <a href="[URL]" target="_blank"
         style="display: inline-block; padding: 14px 36px; font-family: Arial, Helvetica, sans-serif; font-size: 17px; font-weight: 500; color: #FFFFFF; text-decoration: none;">
        Button Text
      </a>
    </td>
  </tr>
</table>

Dark Mode — Gmail iOS (Critical)

Gmail App on iOS is a massive platform and the hardest dark mode problem in email. Read this before building any dark-themed email template.

How Gmail iOS dark mode works:

Gmail applies a proprietary color inversion algorithm to emails — it modifies BOTH backgrounds AND text colors
It targets: background-color CSS, bgcolor HTML attributes, color CSS, and <font color=""> tags
There is no opt-out. No meta tag, CSS property, or HTML attribute reliably prevents Gmail iOS from modifying colors
@media (prefers-color-scheme: dark) is ignored by Gmail iOS (works in Gmail Web only)
color-scheme / supported-color-schemes meta tags have no effect on Gmail iOS

What Gmail iOS does NOT touch:

background-image (including linear-gradient()) — this is the only known way to preserve a background color
Actual images (<img> tags) — these render as-is

Techniques we tested and their results:

Technique	Fixes Backgrounds?	Fixes Text?	Verdict
`color-scheme` meta tags	No	No	Useless for Gmail iOS
`bgcolor` on `<table>`/`<td>`	No	N/A	Gmail inverts these too
`background-image: linear-gradient(#color, #color)`	Yes	No	Only reliable background fix
`<font color="">` tags	N/A	No	Gmail overrides them
`@media (prefers-color-scheme: dark)`	N/A	N/A	Gmail iOS ignores entirely

The core problem for dark-themed emails: You can preserve dark backgrounds with the gradient hack, but Gmail will still mute/shift all text colors. The result is dark background + washed-out text — which can look worse than letting Gmail do its full inversion (where at least backgrounds and text have consistent contrast).

Recommendation:

Do not build dark-themed email templates expecting pixel-perfect rendering in Gmail iOS dark mode. It will not happen.
If you build a dark email, accept that Gmail iOS users will see a color-shifted version. Test in HubSpot's "Preview in email client" → Gmail App Dark (iOS 18) to verify it's at least readable.
Consider whether a light-themed template would serve better if Gmail iOS is a priority audience.
Do NOT add background-image gradient hacks, <font> tags, or color-scheme meta tags to "fix" Gmail dark mode — we tested all of these and none produce an acceptable result for dark emails. They create partial fixes that look worse than Gmail's native full inversion.

Dark Mode — Other Clients

Apple Mail: Respects @media (prefers-color-scheme: dark) and color-scheme meta — progressive enhancement works here
Outlook.com / Outlook mobile: Uses [data-ogsc] (text color) and [data-ogsb] (background color) attributes when forcing dark mode. These are Outlook-specific, not Gmail.
Transparent PNGs may become invisible on inverted backgrounds — use solid-background versions or test carefully
For clients that support it, color-scheme: light dark; in CSS is fine as progressive enhancement — just know it does nothing for Gmail iOS

Outlook Specific

Outlook uses Word as its rendering engine — most CSS is ignored
Use <!--[if mso]> conditional comments for Outlook-specific fixes
MSO properties (mso-table-lspace, mso-padding-alt, etc.) are valid for Outlook only
border-radius does not work in Outlook — buttons degrade to rectangular
Background images don't work in Outlook without VML (Vector Markup Language) hacks

[Company] Brand Adaptation for Email

Since email clients have limited CSS support, adapt the brand system. Pull every color value from /brain/brand-guide/brand-guide.md — never hardcode them into the skill or reuse values from a previous build:

Brand Element	Website	Email Adaptation
Background	Brand background color	Solid hex from the brand guide — works in email
Font	The brand font (see brand-guide)	`Arial, Helvetica, sans-serif` or another web-safe fallback stack (with `@import` of the brand font as progressive enhancement)
Gradient accent bar	CSS `linear-gradient`	Use a pre-made gradient image (hosted PNG/SVG) or a thin `<img>` element
Gradient text	`background-clip: text`	Not supported — use a solid text color from the brand guide instead
CTA button	Brand CTA color, solid	Styled `<a>` with `{% text %}` fields for URL and copy (see CTA section above)
Accent tag	Solid accent bg + contrasting text	Works with inline styles — solid `background-color` and `color` on the tag element are reliable across clients
Card surfaces	Card surface color with `border-radius`	Use the brand guide's card color as a solid bg. Radius works except Outlook (graceful degradation)
Border	`1px solid` brand border color	Works inline on `<td>`
Social icons	CSS `filter: invert()`	Don't use filter. Host icon PNGs in the correct color and reference directly

CTA Card Blocks

Only simple card-style CTA blocks from the brand guide translate to email. Variants that rely on CSS gradient backgrounds and ambient glows get stripped by email clients — adapt the brand's card CTA pattern with solid background colors and a bulletproof button (see Buttons above).

Gradient Bar as Image

Since CSS gradients don't work in email backgrounds, create the signature gradient as a hosted image:

Create a 600x4px PNG with the brand gradient (colors from the brand guide)
Host it publicly (website or HubSpot File Manager)
Reference as <img src="[gradient-bar-url]" width="600" height="4" style="display: block;" />

Base Template + Variants

All [Company] HubSpot email templates use a base template pattern. The shared foundation (header, gradient bar, CTA, footer) lives in one file, and each email type is a variant that customizes the content area.

Existing Templates

marketing/templates/email-templates/
├── email-base-hubspot.html              ← Base (DO NOT upload — starting point only)
├── [variant]-email.html                 ← One file per email type (classic coded, HubL fields)
└── _previews/                           ← Static HTML previews (not for upload)
    └── [variant]-preview.html

*Iterate locally against `_previews/.html before pushing to HubSpot.** HubSpot round-trips are slow and obscure layout cause-and-effect. Keep the preview faithful to HubSpot's dnd_area wrapping (<td class="dnd-section"> → <td class="dnd-column"> → <td class="dnd-module">`); if a preview doesn't mirror that nesting, fix the preview before debugging layout issues in HubSpot.

Creating a New Email Variant

Duplicate email-base-hubspot.html
Rename it (e.g., product-announcement-hubspot.html)
Update the template annotations:

Set isAvailableForNewContent: true
Update label (e.g., [Company] - Product Announcement)

Replace the content between CONTENT START and CONTENT END with your email-specific sections
Add any extra responsive CSS classes in the media query <style> block if needed
Upload to Design Manager (see Upload Instructions below)

What's Shared (don't modify unless updating brand)

Logo header
Gradient accent bar
CTA button section (styled <a> with {% text %} fields for URL and button copy — marketer edits from sidebar)
Footer (social icons, CAN-SPAM address, unsubscribe, view-as-webpage)
Base styles (id="hs-inline-css") and responsive media queries
Preview text module

What Changes Per Variant

The content area between the gradient bar and CTA
Any variant-specific responsive CSS classes (e.g., .date-col for a two-column date layout)
The preview text default value

Template Structure

Every email template should follow this structure:

1. DOCTYPE + HTML wrapper
2. <head>
   - Meta tags (charset, viewport, X-UA-Compatible)
   - Outlook conditional comments (PixelsPerInch)
   - <style> block with inline-css ID (base styles)
   - <style> block for media queries (responsive)
3. <body> (background color on body + wrapper table)
4. Full-width wrapper table (100% width, centered)
5. Email container table (600px, centered)
   a. Logo header (linked to website)
   b. Content sections
   c. CTA button(s)
   d. Footer (social icons, copyright, unsubscribe)
6. Closing tags

Output Format

Output location: marketing/email/templates/[template-slug]/ — confirm the project slug with the user before creating files.

For Each Template, Provide:

1. Complete HTML file

Production-ready, tested against the constraints above
All styles inlined on elements
Progressive <style> block in head
Responsive media queries in separate <style> block
 comments marking content the user should replace
Placeholder brackets [like this] for variable content

2. Upload instructions

Brief notes on which upload method to use (AI Upload vs. coded template)
Any post-upload adjustments needed in HubSpot's editor
Image hosting requirements (list any images that need public URLs)

For Design Manager (coded templates):

Go to Content > Design Manager (or Marketing > Files and Templates > Design Tools)
Click File > New file
Select HTML + HubL as the file type
In "What are you building?" select Template
Click Template type and select Email
Enter a file name and click Create
Paste the complete template code
Click Publish (top right)
The template will appear in the template picker when creating new marketing emails
All HubL editable fields ({% text %}, {% rich_text %}, {% boolean %}) will appear in the right sidebar when editing an email

3. Testing checklist

[ ] Preview in HubSpot
[ ] Send test email to yourself
[ ] Check rendering in Gmail (web + mobile) — including Gmail App Dark (iOS 18) preview
[ ] Check rendering in Outlook (if audience uses it)
[ ] Check rendering in Apple Mail
[ ] Verify all links work
[ ] Verify images load
[ ] Check mobile responsive behavior

Checklist Before Delivering

[ ] Read /brain/brand-guide/brand-guide.md
[ ] Template annotations present (for coded templates: templateType: email, isAvailableForNewContent: true, label)
[ ] Max width 600px
[ ] Table-based layout only (no flexbox, grid, floats, positioning)
[ ] All critical styles inlined
[ ] No CSS gradients on backgrounds (use images or solid colors)
[ ] No overlapping elements
[ ] No JavaScript
[ ] No filter CSS property
[ ] Font stack includes system-safe fallbacks
[ ] All images use publicly accessible URLs
[ ] All images have alt, width, height, display: block, border: 0
[ ] Bulletproof button pattern used for CTAs
[ ] Social icons are pre-made white PNGs (not filtered)
[ ] Gmail App Dark (iOS 18) preview checked — email is readable (colors will shift, that's expected)
[ ] No transparent PNGs that become invisible on inverted backgrounds
[ ] CAN-SPAM compliant footer (unsubscribe link present)
[ ] Responsive media queries in separate <style> block
[ ] Outlook conditional comments included
[ ] Tested at 600px and mobile widths
[ ] No AI slop patterns in copy (see CLAUDE.md)
[ ] Product claims verified against /brain/truth.md

Subscription Types & List Filtering (Sending)

These rules govern who actually receives an email — separate from how the template is built.

Set the email's Subscription type correctly. HubSpot's send engine auto-filters recipients by the Subscription type field on the email itself, so list-level opt-in filters are redundant: the list defines the candidate pool, the Subscription type field is the actual gate. The type also determines which unsubscribe link the recipient sees and which subscription gets decremented on unsubscribe. Wrong type = unsubscribes hit the wrong list, a compliance and trust risk.
Active-list 'subscriber' filters must account for the tri-state model. HubSpot's Opted out of email: [subscription name] property is null by default (Subscribed / Unsubscribed / Not Specified). A filter for 'subscribers' must use is none of Yes AND check the 'Include records where property is empty' box — otherwise never-unsubscribed contacts are excluded from the list.

MCP Tools: HubSpot Dev, Figma & agent-browser

HubSpot Dev MCP (Documentation & CMS)

Use these tools to look up HubSpot documentation and manage CMS assets:

Search docs — Use mcp__HubSpotDev__search-docs to find HubSpot developer documentation on email modules, template markup, HubL syntax, or any email-related API. Always search before guessing at module paths or field syntax.
Fetch doc page — Use mcp__HubSpotDev__fetch-doc immediately after searching to read the full documentation page. Never skip this step — search results are summaries, not complete docs.
Create a CMS template — Use mcp__HubSpotDev__create-cms-template to scaffold a new email template file. Set templateType to email-template.
List remote contents — Use mcp__HubSpotDev__list-cms-remote-contents to see what templates and assets are already deployed in the HubSpot Design Manager.
Create a CMS module — Use mcp__HubSpotDev__create-cms-module to scaffold a custom email module if needed.

When to use: Before building any email template, search docs to verify module paths (e.g., confirm @hubspot/email_body vs @hubspot/email_text behavior). After building, use list-cms-remote-contents to check for naming conflicts before manual upload.

Figma MCP (Design Input)

When the user provides a Figma URL or references an email design mockup:

Pull design context — Use mcp__figma-remote-mcp__get_design_context to extract layout, colors, typography, and spacing from the Figma mockup. Translate these into email-safe HTML (table-based, inline styles, system fonts).
Take a screenshot — Use mcp__figma-remote-mcp__get_screenshot to see the visual design before building the template.
Get metadata — Use mcp__figma-remote-mcp__get_metadata to understand the section structure and layer hierarchy.

When to use: When the user has an email design in Figma that needs to be converted to a HubSpot-compatible HTML template. Remember: the Figma design will use features email doesn't support (gradients, custom fonts, border-radius) — adapt per the constraints in this skill.

agent-browser (Email Rendering Validation)

After building an email template, use agent-browser to validate rendering:

Open the template — Run agent-browser open <file> to open the HTML email file in the browser.
Test at email width — Run agent-browser set viewport 600 900 to set the viewport to 600px wide (email container width), then run agent-browser screenshot to capture the result.
Test mobile rendering — Run agent-browser set viewport 375 812 and run agent-browser screenshot again to verify responsive behavior.
Full-page capture — Run agent-browser screenshot to capture the entire email template for review.
Check accessibility — Run agent-browser snapshot -i to verify heading structure, link text, and alt text on images.
Console errors — Run agent-browser console to catch any broken image references or CSS issues.

When to use: After building any email template — always use agent-browser to validate in the browser before delivering. This catches layout issues, broken images, and responsive problems before the template reaches HubSpot.

HubSpot Documentation References

Email template markup — CSS handling, responsive structures, required HubL variables
Specify drag and drop areas in a custom email template — dnd_area, dnd_section, dnd_column, dnd_module tags for email
Using modules in templates — module snippets, paths, default modules
Create and edit modules in the design manager — custom module creation, field types, editor options
Build a custom coded template — Design Manager upload workflow
HubSpot's default modules — default module paths and usage
Templates overview — template types, annotations, structure
Using HubL tags to change href — community discussion on HubL in href attributes
Custom coded email — community discussion on coded email template patterns
Adding button module with CTA to custom HTML email — community discussion on button/CTA in coded emails
How to code custom drag & drop email templates — community discussion on dnd email templates

Analytics

Use the analytics skill to pull real email performance data when reviewing or optimizing email templates:

`hubspot-emails.ts` — Open rates, click rates, CTOR, bounce rates, and top-performing emails. Benchmark new templates against historical performance or identify which formats work best.

Example: Before building a new email template, run npx tsx .claude/skills/analytics/scripts/hubspot-emails.ts 90d to see which existing emails had the highest open/click rates, then apply those patterns to the new template.

Mandatory Skill Delegation

Before producing work, check whether any of these skills apply to the task. If they do, load the skill before writing that portion. Do not replicate a skill's logic from memory — load it and apply it.

When the task involves...	Skill to Load	Mandatory?
CTA buttons (placement, centering, tracking, brand CSS)	`hubspot-cta`	Yes — load before adding any CTA to a template
Writing or reviewing email copy/messaging	`copywriting` or `copy-editing`	Yes — load before writing or editing copy
Email sequence strategy, drip campaign logic	`email-sequence`	Yes — load when the email is part of a sequence
Visual design decisions beyond what's in the brand guide	`brand-design`	Yes — load for custom visual asset work
Landing page templates (different constraints)	`hubspot-landing-page`	Load if the user asks about landing pages to avoid applying email constraints

Learnings

Is hubspot-email safe to install?

HubSpot Email Templates

Before Building

1. Email Type

2. Content

3. Upload Method

HubSpot AI Upload Limitations

What DOES Transfer Well

HubSpot Coded Template Requirements

Template Annotations (Design Manager)

HubL Editable Fields

Email Template Validator — Rejected Patterns

Personalization Token — Greeting Pattern

Default Email Modules Reference

CTA Buttons in Email Templates

Drag-and-Drop (dnd_area) Email Templates

When to Use dnd_area

Required <head> Includes

Constraints

Architecture Pattern

Static-vs-dnd Horizontal Alignment Gotcha

Pre-placed vs. Dragged Module Width

Module Paths for dnd Email

Syntax Examples

dnd_section Parameters

Required CAN-SPAM Footer Variables

Required Links

Preview Text

CSS Inlining

Email HTML Best Practices

Layout

CSS

Typography

Images

Icons

Buttons

Dark Mode — Gmail iOS (Critical)

Dark Mode — Other Clients

Outlook Specific

[Company] Brand Adaptation for Email

CTA Card Blocks

Gradient Bar as Image

Base Template + Variants

Existing Templates

Creating a New Email Variant

What's Shared (don't modify unless updating brand)

What Changes Per Variant

Template Structure

Output Format

For Each Template, Provide:

Checklist Before Delivering

Subscription Types & List Filtering (Sending)

MCP Tools: HubSpot Dev, Figma & agent-browser

HubSpot Dev MCP (Documentation & CMS)

Figma MCP (Design Input)

agent-browser (Email Rendering Validation)

HubSpot Documentation References

Analytics

Mandatory Skill Delegation

Learnings

Audit the pieces. Scan the whole. Decide.

Required `<head>` Includes