Glossary · Web & App Development
MJML
Overview
What MJML is
MJML is an open-source framework, created by the team behind Mailjet (now part of Sinch), for writing responsive email in a simpler syntax than raw HTML. Instead of hand-coding nested tables and inline styles, developers use semantic components such as mj-section, mj-column, mj-text, and mj-button.
The MJML compiler transforms this markup into standards-compliant, responsive HTML that behaves consistently across major email clients. It is released under the MIT license and is free to use.
How MJML works
You author an .mjml file using MJML's tags, then run it through the MJML engine, available as a Node.js library, a command-line tool, an online editor, and plugins for various editors. The engine outputs the final HTML you send through your ESP or email platform.
Because MJML handles the layout math and cross-client workarounds, its output is responsive by default and adapts columns for mobile. It can be integrated into build pipelines and templating systems so teams generate consistent emails programmatically.
Why MJML matters
Coding email by hand is notoriously difficult because email clients support HTML and CSS inconsistently, often requiring table-based layouts and ghost tables for Outlook. MJML removes much of that friction, letting teams ship responsive emails faster with fewer rendering bugs.
MJML reduces rendering problems but does not eliminate the need for testing; teams still validate output in tools like Litmus or Email on Acid. Alternatives include Foundation for Emails and hand-coded frameworks, but MJML is among the most widely adopted.
Where we use it
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How our team puts MJML to work in real projects.
FAQ
MJML — common questions
Is MJML free to use?
Yes. MJML is open-source software released under the MIT license, free to use in commercial and personal projects. It is maintained by the team behind Mailjet, part of Sinch.
What problem does MJML solve?
MJML solves the difficulty of coding responsive HTML email that renders consistently across inconsistent email clients. It compiles simple component tags into the complex table-based HTML those clients require.
Do I still need to test MJML emails?
Yes. MJML produces reliable output but cannot guarantee perfect rendering everywhere, so testing in a platform like Litmus or Email on Acid before sending is still recommended.
Need MJML done right?
Book a free consultation and we’ll map the fastest, most cost-effective path for your project.
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