MJML

Key points

• Category: Design, templates & testing
• Pricing: Free
• Best for: Developers hand-building templates.
• Open source
• Responsive by default
• CLI and integrations

What MJML is

MJML (Mailjet Markup Language) is a free, open-source markup language and compiler created by Mailjet that generates responsive HTML email code from a simplified, component-based syntax. Its engine abstracts away the notoriously fragile table-based HTML/CSS required for cross-client email compatibility, translating semantic tags like mj-section and mj-column into tested, responsive HTML. It is installable via npm for Node.js or the CLI, has an online live editor, and is released under the MIT license with an active open-source community (18,000+ GitHub stars).

Developers and email engineers use MJML to hand-code responsive templates faster than writing raw HTML, often integrating it into build pipelines, static site generators, or frameworks like React (via mjml-react) and Python/Django bindings. It ships a large library of pre-built responsive components (buttons, carousels, accordions, navbars) and integrates with editors like VS Code, plus ports in Rust, .NET, Ruby and Elixir for use in different tech stacks.

It sits in the design, templates & testing part of an email stack - build emails that render and read well everywhere. In practice it is the right pick when your priority is: developers hand-building templates.

What it does well

The capabilities teams rely on most are open source, responsive by default, cli and integrations. Taken together these cover the day-to-day work in this category, and they are the features worth testing during a trial rather than reading about.

MJML is best for developers who want full code control over responsive, cross-client email HTML without hand-writing table hacks; being open source and free, it is the standard choice for engineering teams building custom email tooling or in-house template systems.

In real use the strongest points people report are free; removes most rendering pain.

Key features

• Open source
• Responsive by default
• CLI and integrations
• Free
• Removes most rendering pain

Pricing tiers

MJML is a free product. MJML is completely free and open source; there are no paid tiers for the core framework, though some third-party tools and hosted editors built on top of it may charge separately.

Pricing pages move often, so confirm the current figures with the vendor before you budget. The number worth modelling is not the licence fee on its own but the cost per delivered email once bounces, suppressed contacts and spam-foldered sends are taken out.

Ideal customer profile

• Best fit: Developers hand-building templates.
• Where it sits in the stack: Design, templates & testing - build emails that render and read well everywhere.
• Budget profile: Free - suited to teams comfortable with this commercial model.
• Probably not for you if: requires a build step would block your team.

What it connects to

MJML is commonly wired into Node.js/npm, React (mjml-react), Python/Django (django-mjml), PHP/Laravel MJML, Visual Studio Code, Gulp, Parcel, Rust (MRML), .NET (MJML.NET) and Ruby (MRML Ruby). Check that the specific objects and events you rely on are covered, not just that a logo appears on the integrations page - shallow connectors are a frequent source of rework.

Where it falls short

No tool in this space is complete on its own. With MJML the trade-offs to plan around are requires a build step. None of these are reasons to avoid it - they are the gaps another layer of your stack needs to fill.

It requires coding knowledge and a build step, unlike drag-and-drop builders, and it produces HTML only - it includes no visual drag-and-drop editor for non-technical users, no built-in rendering preview across real clients, and no spam or deliverability testing, so output still needs external QA.

A useful test before committing: send a real campaign through your intended setup, then check where it actually lands across Gmail, Outlook, Yahoo and your customers' corporate filters. Tooling that looks identical on a feature list often behaves very differently once reputation and authentication are involved.

The essentials

Category

Design, templates & testing

Pricing model

Free

Vendor

mjml.io

G2 rating

Not listed

Best for

Developers hand-building templates.

Works alongside Warmy

Yes - warm-up, placement, DMARC

How it fits a deliverability stack

Deliverability is decided by four things: the reputation of the sending domain and mailbox, the quality of the list, correct SPF, DKIM and DMARC authentication, and proof of where mail actually lands. MJML covers part of that picture. The mistake most teams make is buying four separate products for those four jobs and still having no single place that tells them whether the last campaign reached the inbox.

Warmy runs warm-up, inbox placement testing, email verification and DMARC monitoring as one platform, which is why MJML usually sits alongside it rather than against it: it keeps doing what it is good at, while reputation, placement and authentication are handled in one loop.

MJML only generates well-structured, client-compatible HTML markup; it has no relationship to sender reputation, authentication (SPF/DKIM/DMARC), or inbox placement, and teams must pair it with separate rendering/spam testing tools and an ESP or sending infrastructure for actual deliverability.