MJML
Email markup language that compiles to cross-client responsive HTML email. Writing HTML emails that work across Gmail, Outlook, iOS Mail, and others requires complex table-based layouts with client-specific hacks. MJML provides a high-level XML-like syntax (mj-section, mj-column, mj-image) that compiles to bulletproof email HTML. Node.js API and CLI available. Alternative to React Email for non-React stacks.
Score Breakdown
⚙ Agent Friendliness
🔒 Security
Template injection risk if MJML templates include untrusted user content — sanitize before compilation. Local compilation has no network security concerns.
⚡ Reliability
Best When
You need cross-client responsive HTML emails without hand-coding complex table layouts — MJML dramatically reduces email HTML complexity.
Avoid When
Your team prefers React component syntax — use React Email instead. Or if emails are simple enough that plain HTML suffices.
Use Cases
- • Compile MJML templates to production-ready email HTML in agent email delivery pipelines without manual email client testing
- • Build responsive email templates for transactional emails (receipts, notifications, password resets) that work in all clients
- • Generate personalized email HTML from MJML templates with dynamic content injection in backend agents
- • Maintain a library of reusable email components (headers, footers, CTAs) that compile consistently across email clients
- • Replace complex inline-style table-based email HTML with readable MJML markup in email marketing workflows
Not For
- • React-based email workflows — React Email (by Resend) offers the same benefits with React component syntax
- • Plain text emails or simple notification emails where HTML complexity is unnecessary
- • Real-time email preview in browser — use MJML's online editor or integrate with email testing tools
Interface
Authentication
No authentication — local compilation tool. MJML API (online service) is separate with API key auth.
Pricing
npm package is free. The optional cloud rendering API has usage-based pricing.
Agent Metadata
Known Gotchas
- ⚠ MJML custom components require registration before compilation — using custom components without registration produces empty output without error
- ⚠ Dynamic content (personalization tokens like {{name}}) must be injected after MJML compilation, not inside MJML attributes — MJML is a template compiler not a template engine
- ⚠ MJML outputs complete HTML documents with <html><body> — when embedding in email APIs (SendGrid, Postmark), use the compiled body content only
- ⚠ mj-text supports limited HTML — complex HTML inside mj-text (nested tables, custom CSS) may not render correctly in all clients
- ⚠ MJML v4 dropped support for mj-container — legacy templates using this element must be migrated to mj-section
- ⚠ Line wrapping in output HTML is intentional for email client compatibility — don't minify MJML output HTML as some email clients have line length limits
Alternatives
Full Evaluation Report
Detailed scoring breakdown, competitive positioning, security analysis, and improvement recommendations for MJML.
Scores are editorial opinions as of 2026-03-06.