Emailens

MCP server for email compatibility analysis. Analyze, preview, diff, and fix HTML emails across 21 email clients — plus capture real screenshots and create shareable links with an optional API key.

Why your assistant needs this: across the 255 CSS and HTML features we track, only 6 are fully supported in every major email client (see the data). Ask Claude to check your email before you send it.

Built on @emailens/engine. Also available as a GitHub Action.

Install

npx -y @emailens/mcp

Setup

Claude Desktop

Add to claude_desktop_config.json:

{
  "mcpServers": {
    "emailens": {
      "command": "npx",
      "args": ["-y", "@emailens/mcp"]
    }
  }
}

Claude Code

claude mcp add emailens -- npx -y @emailens/mcp

With API Key (optional — unlocks screenshots + sharing)

{
  "mcpServers": {
    "emailens": {
      "command": "npx",
      "args": ["-y", "@emailens/mcp"],
      "env": {
        "EMAILENS_API_KEY": "ek_live_..."
      }
    }
  }
}

Get your free API key at emailens.dev/settings/api-keys.

Remote (no install)

Use the hosted endpoint — no npm or Node.js needed. API key required.

{
  "mcpServers": {
    "emailens": {
      "url": "https://emailens.dev/api/mcp",
      "headers": {
        "Authorization": "Bearer ek_live_..."
      }
    }
  }
}

Tools

Local Tools (no account needed)

preview_email

Full email compatibility preview — transforms HTML for 21 clients, analyzes CSS, generates scores, simulates dark mode, checks inbox preview and email size.

Parameter	Type	Required	Description
html	string	Yes	Email HTML source
clients	string[]	No	Filter to specific client IDs
format	enum	No	"html", "jsx", "mjml", "maizzle"

analyze_email

Quick CSS compatibility analysis — returns per-client scores and warnings. Faster than audit_email when you only need CSS compatibility.

Parameter	Type	Required	Description
html	string	Yes	Email HTML source
format	enum	No	Input format

audit_email

Comprehensive quality audit — CSS compatibility, spam scoring, link validation, accessibility, images, inbox preview, size (Gmail clipping), template variables, content overflow, and visual bugs.

Parameter	Type	Required	Description
html	string	Yes	Email HTML source
format	enum	No	Input format
skip	string[]	No	Checks to skip (e.g. ["spam", "images"])

fix_email

Generate a structured fix prompt for compatibility issues. Returns markdown with fix instructions that the AI can apply directly.

Parameter	Type	Required	Description
html	string	Yes	Email HTML to fix
format	enum	No	Controls fix syntax
scope	enum	No	"all" or "current"
selectedClientId	string	No	Client ID for scoped fixes

list_clients

List all 21 supported email clients with IDs, names, engines, and dark mode support.

diff_emails

Compare two email HTML versions — shows score changes, fixed issues, and introduced issues per client.

Parameter	Type	Required	Description
before	string	Yes	Original email HTML
after	string	Yes	Modified email HTML
format	enum	No	Input format

check_deliverability

Check email deliverability for a domain — SPF, DKIM, DMARC, MX, BIMI records with a score and actionable issues.

Parameter	Type	Required	Description
domain	string	Yes	Domain to check (e.g. "company.com")

Hosted Tools (require EMAILENS_API_KEY)

capture_screenshots

Capture real email screenshots across 21 clients in real browsers. Screenshots are hosted on CDN.

Parameter	Type	Required	Description
html	string	Yes	Email HTML source
format	enum	No	Input format
clients	string[]	No	Filter clients
modes	string[]	No	["light"], ["dark"], or ["light", "dark"]
title	string	No	Name for the preview

Free plan: 30 previews/day. Sign up

share_preview

Create a shareable link. Recipients see the full analysis without an account.

Parameter	Type	Required	Description
html	string	Yes	Email HTML source
title	string	No	Display title
format	enum	No	Input format

Requires Dev plan ($9/mo). Share links expire after 7 days (Dev) or never (Pro).

Supported Email Clients (21)

Client	ID	Dark Mode	Notes
Gmail	gmail-web	Yes
Gmail Android	gmail-android	Yes
Gmail iOS	gmail-ios	Yes
Outlook 365	outlook-web	Yes
Outlook Windows	outlook-windows	No
Outlook Windows Legacy	outlook-windows-legacy	No	Deprecated Oct 2026
Outlook iOS	outlook-ios	Yes	New in v0.4.0
Outlook Android	outlook-android	Yes	New in v0.4.0
Outlook for Mac	outlook-macos	Yes	New in v0.10.0
Apple Mail	apple-mail-macos	Yes
Apple Mail iOS	apple-mail-ios	Yes
Yahoo Mail	yahoo-mail	Yes
Yahoo Mail Android	yahoo-mail-android	Yes	New in v0.10.0
Yahoo Mail iOS	yahoo-mail-ios	Yes	New in v0.10.0
Samsung Mail	samsung-mail	Yes
Thunderbird	thunderbird	No
HEY Mail	hey-mail	Yes
Proton Mail	protonmail	Yes	New in v0.10.0
AOL Mail	aol	Yes	New in v0.10.0
Fastmail	fastmail	Yes	New in v0.10.0
Superhuman	superhuman	Yes

Development

bun install
bun run build
bun test
bun run typecheck

License

MIT

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