Emailens

The rendering linter for email

Quick Start · What It Catches · Why Emailens · Supported Clients · API Docs

Your email looks perfect in Apple Mail. Gmail strips half the CSS. Outlook renders it in Word.

@emailens/engine analyzes HTML, React Email, MJML, and Maizzle against 21 email clients and scores compatibility before your email goes out. It catches the issues in the engine, in the terminal, in CI, and inside AI coding workflows.

If you want the fastest path to trying it locally, start with the CLI:

npx @emailens/cli lint email.html

The CLI is the recommended entry point for open-source usage. The engine is the lower-level library for builders, tools, and custom integrations.

emailens.dev is the hosted SaaS for shared previews, screenshots, visual diffs, and team workflows. The open-source packages are the local developer tooling.

Quick Start

Option 1: Try the CLI first

npx @emailens/cli lint email.html

Option 2: Use the engine as a library

npm install @emailens/engine

import { auditEmail } from "@emailens/engine";

const html = `<html><body><div style="display:flex; gap: 12px;">...</div></body></html>`;
const report = auditEmail(html, { framework: "jsx" });

console.log(report.compatibility.scores["outlook-windows"]);

The main entry runs in the browser as well as in Node, and a test keeps it that way. The Node-only parts live in subpaths: @emailens/engine/compile (React Email, MJML and Maizzle compilers) and @emailens/engine/server (DNS and SpamAssassin checks).

What It Catches

• CSS compatibility across 21 clients
• Spam scoring and content hygiene signals
• Accessibility checks for contrast and semantics
• Image and link validation
• Inbox preview and client-specific rendering issues
• Template variable and overflow problems
• AI fix generation for structural issues

Every finding may include source positions, so a result can be pointed at, annotated, or fixed in place.

Why Emailens?

• Offline-first: runs locally with no account required
• Unified audit: a single tool checks CSS, spam, accessibility, links, images, and more
• Framework-aware: works with raw HTML, React Email, MJML, and Maizzle
• AI-ready: structural fixes can be generated with any model provider
• Programmable: use it in CI, editors, scripts, or custom tooling

Supported Email Clients

Each client links to its support page on emailens.dev, built from this package's data. Every feature across all 21 clients: emailens.dev/email-css.

Client	ID
Gmail	gmail-web
Gmail Android	gmail-android
Gmail iOS	gmail-ios
Outlook 365	outlook-web
Outlook (New)	outlook-windows
Outlook Classic	outlook-windows-legacy
Outlook iOS	outlook-ios
Outlook Android	outlook-android
Outlook for Mac	outlook-macos
Apple Mail	apple-mail-macos
Apple Mail iOS	apple-mail-ios
Yahoo Mail

Ecosystem

Package	Use it for
@emailens/engine	Core library and analysis API
@emailens/cli	Lint locally and in CI
@emailens/mcp	AI agent access to email QA
emailens/action	GitHub Action quality gate
emailens/vscode	VS Code linting and preview
emailens.dev	Hosted previews and team workflows

License

MIT, Copyright 2025 Emailens

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