# Emailens

> Email QA SaaS that previews how HTML emails render across Gmail, Outlook, Apple Mail, Yahoo, Samsung Mail, and Thunderbird. Transforms CSS per-client, scores compatibility (0-100), simulates dark mode, and captures screenshots. Available as a web app, REST API, MCP server, and GitHub Action.

- [Full Documentation (raw text)](https://docs.emailens.dev/llms-full.txt): Complete documentation in a single file for AI models and LLM ingestion.

## Docs

- [Introduction](https://docs.emailens.dev/): Emailens is an email QA tool that previews how HTML emails render across 21 email clients including Gmail, Outlook, Apple Mail, Yahoo, HEY Mail, Superhuman, and more.
- [Authentication](https://docs.emailens.dev/api/authentication): Authenticate with the Emailens API using API keys or session cookies.
- [Error Handling](https://docs.emailens.dev/api/errors): HTTP status codes and error response format for the Emailens API.
- [Pre-send gate](https://docs.emailens.dev/api/gate): One boolean and the reasons, for CI, Zapier or a send script.
- [REST API Reference](https://docs.emailens.dev/api): Complete reference for the Emailens REST API, preview emails, manage API keys, audit domains, and create share links.
- [Rate Limiting](https://docs.emailens.dev/api/rate-limiting): Rate limits, daily quotas, and how to handle 429 responses.
- [CLI](https://docs.emailens.dev/cli): Install and use @emailens/cli to analyze, preview, audit, and lint HTML emails in the terminal.
- [CLI project config](https://docs.emailens.dev/cli/project-config): Share lint severity and skip rules between the CLI and VS Code extension via .emailensrc or package.json.
- [Previewing Apple Mail with Emailens](https://docs.emailens.dev/email-clients/apple-mail): How Emailens simulates Apple Mail on macOS and iOS, and what its WebKit rendering means for your previews.
- [Previewing Gmail with Emailens](https://docs.emailens.dev/email-clients/gmail): How Emailens simulates Gmail Web, Android, and iOS: which variants are covered, what the preview transforms, and how to read the results.
- [Previewing email clients with Emailens](https://docs.emailens.dev/email-clients): How Emailens simulates each of the 21 supported email clients: coverage, variants, and how to read preview output.
- [Previewing Outlook with Emailens](https://docs.emailens.dev/email-clients/outlook): How Emailens simulates Outlook 365 Web, Outlook (New), and Outlook Classic, including the Word-engine differences the preview reproduces.
- [Previewing Samsung Mail with Emailens](https://docs.emailens.dev/email-clients/samsung-mail): How Emailens simulates Samsung Mail and what its rendering quirks mean for your previews.
- [Previewing Thunderbird with Emailens](https://docs.emailens.dev/email-clients/thunderbird): How Emailens simulates Thunderbird and how its Gecko rendering shows up in previews.
- [Previewing Yahoo Mail with Emailens](https://docs.emailens.dev/email-clients/yahoo-mail): How Emailens simulates Yahoo Mail across web and mobile, and how to interpret its preview output.
- [Analyze & Score](https://docs.emailens.dev/engine/analyze): Detect CSS compatibility issues and generate per-client compatibility scores, with optional framework-aware fix snippets.
- [Code Fixes](https://docs.emailens.dev/engine/code-fixes): Get actionable before/after code snippets to fix CSS compatibility issues, with framework-aware suggestions for React Email, MJML, and Maizzle.
- [CSS Support Matrix](https://docs.emailens.dev/engine/css-support-matrix): Which CSS properties are supported, partially supported, or unsupported in each email client.
- [Dark Mode Simulation](https://docs.emailens.dev/engine/dark-mode): Simulate how email clients render your email in dark mode.
- [Diff Results](https://docs.emailens.dev/engine/diff): Compare two sets of transform results to see what improved or regressed.
- [LLM Export](https://docs.emailens.dev/engine/export-prompt): Generate LLM-ready prompts from email analysis results for automated fixing.
- [Engine Package](https://docs.emailens.dev/engine): @emailens/engine is the core library for email transformation, analysis, scoring, dark mode simulation, and framework-aware code fixes.
- [Transform](https://docs.emailens.dev/engine/transform): Transform HTML emails for specific email clients with per-client CSS rewriting.
- [Core Concepts](https://docs.emailens.dev/getting-started/concepts): Understand how Emailens transforms, analyzes, and scores email compatibility.
- [Your First Preview](https://docs.emailens.dev/getting-started/first-preview): Step-by-step walkthrough of previewing an HTML email across all supported clients.
- [Quick Start](https://docs.emailens.dev/getting-started): Get your first email preview or AI-generated template in under a minute using the Emailens web app, MCP, or REST API.
- [Installation](https://docs.emailens.dev/getting-started/installation): Set up Emailens for your project , API keys, engine package, MCP server, or GitHub Action.
- [Workflow Examples](https://docs.emailens.dev/github-action/examples): Example GitHub Actions workflows for common email testing scenarios.
- [GitHub Action](https://docs.emailens.dev/github-action): Fail PRs when HTML email templates have rendering issues across email clients.
- [Inputs & Outputs](https://docs.emailens.dev/github-action/inputs-outputs): Complete reference for GitHub Action inputs and outputs.
- [GitHub Action Setup](https://docs.emailens.dev/github-action/setup): Step-by-step guide to adding the Emailens email check to your CI pipeline.
- [Dark Mode Guide](https://docs.emailens.dev/guides/dark-mode-guide): Make your HTML emails look good in dark mode across all email clients.
- [Email Best Practices](https://docs.emailens.dev/guides/email-best-practices): Write HTML emails that render well across all major email clients.
- [Fixing Compatibility Issues](https://docs.emailens.dev/guides/fixing-compatibility): How to use Emailens warnings and framework-aware code fixes to improve email client compatibility.
- [Migration from Litmus](https://docs.emailens.dev/guides/migration-from-litmus): Switching from Litmus or Email on Acid to Emailens for email QA and compatibility testing.
- [Chrome Extension](https://docs.emailens.dev/integrations/chrome-extension): Seamless, one-click email audits directly from Klaviyo, HubSpot, Mailchimp, or any webpage with the Emailens Chrome Extension.
- [CI/CD Integration](https://docs.emailens.dev/integrations/ci-cd): Integrate Emailens into your continuous integration pipeline beyond GitHub Actions.
- [Maizzle](https://docs.emailens.dev/integrations/maizzle): Preview Maizzle templates with Emailens , submit Maizzle source directly and get framework-aware fix snippets.
- [MJML](https://docs.emailens.dev/integrations/mjml): Preview MJML templates with Emailens , submit MJML directly and get framework-aware fix snippets.
- [React Email](https://docs.emailens.dev/integrations/react-email): Lint React Email templates against 21 email clients, locally and in CI, by checking the HTML that React Email exports.
- [VS Code extension](https://docs.emailens.dev/integrations/vscode-extension): Open-source Emailens extension for live email preview and linting in VS Code.
- [Workflows](https://docs.emailens.dev/mcp/claude-integration): Example workflows for using Emailens MCP tools with Claude and other AI assistants.
- [MCP Server](https://docs.emailens.dev/mcp): Use Emailens with Claude Desktop, Claude Code, Cursor, and other MCP-compatible AI assistants.
- [MCP Setup](https://docs.emailens.dev/mcp/setup): Install and connect the Emailens MCP server to Claude Desktop, Claude Code, or any MCP client.
- [MCP Tools Reference](https://docs.emailens.dev/mcp/tools): Detailed reference for all 13 Emailens MCP tools, 7 local and 6 hosted.
- [Pricing & Plans](https://docs.emailens.dev/pricing): Compare Free, Dev, Pro, and Team plan allowances, AI quotas, API keys, and feature entitlements.
- [Changelog](https://docs.emailens.dev/reference/changelog): Release notes and version history for Emailens.
- [Client Reference](https://docs.emailens.dev/reference/clients): Complete reference for all 21 supported email clients with their properties.
- [CSS Properties](https://docs.emailens.dev/reference/css-properties): CSS support levels for each property across all 21 email clients (298 features tracked).
- [TypeScript Types](https://docs.emailens.dev/reference/types): Complete TypeScript type reference for @emailens/engine.
- [AI Agent Integration (MCP)](https://docs.emailens.dev/sandbox/ai-agents): Allow AI coding agents (Claude, Cursor, Windsurf) to inspect sandbox inboxes and run end-to-end authentication tests via Model Context Protocol.
- [Automated Testing in CI/CD](https://docs.emailens.dev/sandbox/automated-testing): Run end-to-end authentication and transaction tests with Playwright, Cypress, or Vitest using the Emailens wait API.
- [SMTP Credentials & Rotation](https://docs.emailens.dev/sandbox/credentials): Provision per-service credentials, enforce STARTTLS transit encryption, and rotate credentials with zero downtime.
- [Direct Email Inbound Sandbox](https://docs.emailens.dev/sandbox/email-inbox): Capture staging emails directly through custom MX addresses on try.emailens.dev without running an SMTP client.
- [Email Sandbox Overview](https://docs.emailens.dev/sandbox): Capture, inspect, and simulate staging and test emails using dedicated Inbound MX inboxes or an authenticated SMTP relay.
- [Authenticated SMTP Relay](https://docs.emailens.dev/sandbox/smtp-relay): Route outbound emails from your development backend, framework, or Docker container to the Emailens sandbox SMTP server.
- [AI Email Builder](https://docs.emailens.dev/web-app/ai-builder): Generate clean, multi-client email templates with automated engine audits and iterative repair loops.
- [API Keys & MCP Management](https://docs.emailens.dev/web-app/api-keys): Manage API keys, monitor 30-day traffic split between REST and MCP, and test server connections.
- [Dark Mode Simulation & Contrast](https://docs.emailens.dev/web-app/dark-mode-preview): Preview client-specific dark mode transformations across WebKit, Blink, and Gecko engines with contrast warnings.
- [Dashboard & Preview History](https://docs.emailens.dev/web-app/dashboard): Manage saved email previews, compare versions with visual diffs, and monitor daily quota usage.
- [DMARC Reports](https://docs.emailens.dev/web-app/dmarc-reports): Send your domain's DMARC aggregate reports to Emailens and see how much of your real mail passes, and who else is sending as you.
- [Domain Deliverability & Monitoring](https://docs.emailens.dev/web-app/domains): Monitor SPF, DKIM, DMARC, MX, and BIMI DNS records with automated drift detection and email alerts.
- [Web App Overview](https://docs.emailens.dev/web-app): Use the Emailens web app to build, preview, analyze, and debug emails across all 21 major email clients.
- [Preview Tool & Linter](https://docs.emailens.dev/web-app/preview-tool): Test HTML, React Email, MJML, and Maizzle templates with side-by-side rendering and 14-point quality audits.
- [Real-Device Checks](https://docs.emailens.dev/web-app/real-device-checks): Screenshot your email in real Outlook, Apple Mail, iPhone and webmail, right next to the simulation.
- [Sharing Previews](https://docs.emailens.dev/web-app/sharing): Create public, collaborative preview links with client switching and password protection.