analyze_email
Quick CSS compatibility analysis — returns warnings and per-client scores. Use audit_email for full quality report (spam, links, a11y, images, etc.).
LABSCO SUMMARY
The findings are grouped by problem rather than repeated per client, which is the difference between a usable response and an unreadable one.
The authors are unusually explicit about why: a single border-radius on an ordinary newsletter used to arrive twelve times — two clients that drop it, six selectors that use it — and the response for an 11KB email came to 286KB. Grouping by property, severity and message, and moving fix snippets into the separate fix tool, brought that to 40KB. The same economy shapes the source positions: the first occurrence is full, the rest are line numbers, because a real newsletter can produce over a thousand of them. Then the diff tool closes the loop — it says which issues the fix resolved and which it introduced, which is the step that usually goes missing.
What it is
An email QA server that takes HTML, MJML, Maizzle or React Email, compiles it, and returns compatibility, quality and deliverability reports across 21 email clients including Gmail, Outlook, Apple Mail, Yahoo, Samsung, Thunderbird, HEY, Proton Mail, AOL, Fastmail and Superhuman.
What you get
- Compatibility at either depth: a quick CSS analysis returning per-client scores and one finding per problem, or a full preview that transforms the HTML per client and adds dark-mode simulation, inbox preview and email size (analyze_email, preview_email).
- Findings that carry their location — line, column, offset and length for the first occurrence, plus the line numbers of the rest — so an assistant edits the exact source rather than searching for it. Positions are reported for HTML input only, because a compiled template's line numbers would point into generated output.
- A quality audit past the CSS: spam scoring, link validation, accessibility, images, inbox preview, Gmail clipping by size and template variables, with a skip parameter to drop individual checks (audit_email).
- A closed fix loop: a structured fix prompt carrying the original code, the detected CSS or structural issues and fix snippets, then a comparison of two versions showing score changes, issues resolved and issues newly introduced per client (fix_email, diff_emails).
- Domain-side deliverability read straight from DNS — SPF, DKIM, DMARC, MX and BIMI — returning a score out of 100 and the issues behind it, with no key needed (check_deliverability).
- Rendered evidence rather than described evidence: real browser screenshots across the 21 clients in light and dark variants, hosted on a CDN, and a shareable analysis link a recipient opens without an account (capture_screenshots, share_preview).
- The supported clients with their IDs, engines and dark-mode support — which is what the client filters on the other tools take, and an unknown ID is rejected by name rather than returning an empty pass (list_clients).
Requirements
Nothing for the analysis and the DNS checks — npx -y @emailens/mcp and they work. Screenshots and shareable links need an EMAILENS_API_KEY, free to obtain, with sharing on the paid Dev plan. A hosted endpoint at https://emailens.dev/api/mcp needs no Node.js at all, but does require the key as a Bearer token.
Setup effort
One command — npx -y @emailens/mcp
USE CASES
01
Checking a newsletter before it goes to the list
Per-client scores with the failing property named and the line it sits on.
02
Fixing a rendering problem and proving the fix worked
Get the fix prompt for the issues you chose to act on, then diff the two versions.
03
Finding out why the email is landing in spam
Spam scoring on the content, and SPF, DKIM, DMARC and BIMI on the sending domain.
04
Showing a stakeholder what it will actually look like
Real screenshots across clients in light and dark, or a link they open without an account.
05
Checking only the clients your audience uses
Take the client IDs first, then filter the report to them — which also roughly halves the response.
06
Reviewing a template written in MJML or React Email
It is compiled first, so what gets checked is the HTML your readers actually receive.
9 tools
Counted once with only startup setup. Other versions, modes or optional credentials may expose a different list.
audit_email
Comprehensive email quality audit — CSS compatibility, spam scoring, link validation, accessibility, images, inbox preview, size (Gmail clipping), and template variables. Use skip to omit specific checks.
capture_screenshots
Capture real email screenshots across 21 clients (Gmail, Outlook, Apple Mail, etc.) with light and dark mode variants. Screenshots are rendered in real browsers and hosted on CDN. Requires EMAILENS_API_KEY env var — free plan at emailens.dev?ref=mcp.
check_deliverability
Check email deliverability for a domain — SPF, DKIM, DMARC, MX, and BIMI records. Returns a score (0-100) and actionable issues. Uses DNS lookups (no API key needed).
diff_emails
Compare two email HTML versions — shows score changes, fixed issues, and newly introduced issues per client. Use after making fixes to verify improvements.
fix_email
Generate a structured fix prompt for email compatibility issues. Returns markdown with the original code, detected issues (CSS or structural), fix snippets, and format-specific instructions. Use after preview_email or analyze_email.
list_clients
List the supported email clients (the README's table counts 21) with IDs, names, engines, and dark mode support.
preview_email
Full email compatibility preview — transforms HTML for 21 email clients (Gmail, Outlook, Apple Mail, Yahoo, Samsung, Thunderbird, HEY, Proton Mail, AOL, Fastmail, Superhuman), analyzes CSS, generates scores, simulates dark mode, checks inbox preview and email size.
share_preview
Create a shareable link for an email preview. Recipients see the full analysis without needing an account. Requires EMAILENS_API_KEY env var and Dev plan ($9/mo).
BEFORE YOU INSTALL
What to know first
Tools you get
9 tools when we connected. capture_screenshots and share_preview need EMAILENS_API_KEY, and share_preview also needs the Dev plan ($9/mo). MJML, Maizzle and React Email input compiles only if you install those compilers yourself.
Requires
npx on PATH
Optional
EMAILENS_API_KEY in your environment
Where it runs
Of the 3 documented clients, 2 run the server on your machine and 1 connects to a hosted endpoint.
CONTEXT COST
Light Standing cost
Rated by the size of the 9 tool definitions that ride along on every turn, not by how many there are
INSTALLATION
Connect your client
Server setup
npx
TERMINAL
npx -y @emailens/mcpHosted endpoint
ENDPOINT URL
https://emailens.dev/api/mcpAdd this hosted endpoint to your MCP client using the credentials listed under Requirements.
MCP Clients
Claude Desktop
CLAUDE DESKTOP · JSON
{
"mcpServers": {
"emailens": {
"command": "npx",
"args": [
"-y",
"@emailens/mcp"
]
}
}
}Claude Code
CLAUDE CODE · TERMINAL
claude mcp add emailens -- npx -y @emailens/mcpAny MCP client — hosted
ANY MCP CLIENT — HOSTED · JSON
{
"mcpServers": {
"emailens": {
"url": "https://emailens.dev/api/mcp",
"headers": {
"Authorization": "Bearer <YOUR_TOKEN>"
}
}
}
}The hosted endpoint requires an API key: <YOUR_TOKEN> is your Emailens API key (the same value as EMAILENS_API_KEY), free at emailens.dev/settings/api-keys.
