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MJML-Rails allows you to render HTML emails from an MJML template.

Note: As of MJML 4.3.0 you can no longer use <mj-text> directly inside an <mj-body>, wrap it in <mj-section><mj-column>.

An example template might look like:

<!-- ./app/views/user_mailer/user_signup_confirmation.mjml -->
    <mj-preview>Hello World</mj-preview>
        <mj-text>Hello World</mj-text>
        <%= render partial: "info", formats: [:html] %>

And the partial:

<!-- ./app/views/user_mailer/_info.html.erb -->
<mj-text>This is <%= @user.username %></mj-text>
  • Notice you can use ERB and partials inside the template.

Your user_mailer.rb might look like this:

# ./app/mailers/user_mailer.rb
class UserMailer < ActionMailer::Base
  def user_signup_confirmation
    mail(to: "", from: "") do |format|

Example application


Add it to your Gemfile.

gem 'mjml-rails'

Run the following command to install it:

bundle install

Add the MJML parser to your project with your favourite package manager:

# with npm
npm install mjml

# with yarn
yarn add mjml

MJML-Rails falls back to a global installation of MJML but it is strongly recommended to add MJML directly to your project.

You'll need at least Node.js version 6 for MJML to function properly.


MJML-Rails has the following settings with defaults:

  • template_language: :erb

    ERB can be used inside MJML templates by default. Possible values are all template languages that you have installed, e.g. :haml or :slim.

    Note: If you’re using Haml/Slim layouts, please don’t put <mjml> in comments in your partial. Read more at #34.

  • raise_render_exception: true

    Exceptions will be raised and passed to your application by default.

    Beware that setting it to false leads to an empty html email when an exception is raised, so only set this to false if you do not rely on html (e.g. you have a text fallback for your emails).

  • minify: false

  • beautify: true

  • validation_level: "strict"

    MJML-Rails will raise an exception on any template error by default.

    If set to soft, MJML will render invalid templates and ignore invalid parts. This means in case of an invalid template those invalid parts will be missing from the output.

    See MJML validation documentation for all possible values.

  • mjml_binary: nil

    This can be used to specify the path to a custom MJML binary if it is not detected automatically (shouldn't be needed).

  • mjml_binary_version_support: "4."

    MJML-Rails checks the version of the MJML binary and fails if it does not start with this version, e.g. if an old version is installed by accident.

# config/initializers/mjml.rb
Mjml.setup do |config|
  # Use :haml as a template language
  config.template_language = :haml

  # Ignore errors silently
  config.raise_render_exception = false

  # Optimize the size of your emails
  config.beautify = false
  config.minify = true

  # Render MJML templates with errors
  config.validation_level = "soft"

  # Use custom MJML binary with custom version
  config.mjml_binary = "/path/to/custom/mjml"
  config.mjml_binary_version_supported = "3.3.5"

If you are experiencing slow compilation times, you may want to point directly at your binary:

# config/initializers/mjml.rb
Mjml.setup do |config|
  config.mjml_binary = Rails.root.join("node_modules/mjml/bin/mjml")

MJML v3.x & v4.x support

Version 4.x of this gem brings support for MJML 4.x

Version 2.3.x and 2.4.x of this gem brings support for MJML 3.x

If you'd rather still stick with MJML 2.x then lock the mjml-rails gem:

gem 'mjml-rails', '2.2.0'

For MJML 3.x lock the mjml-rails gem:

gem 'mjml-rails', '2.4.3'

And then to install MJML 3.x

npm install -g mjml@3.3.5

How to guides

Hugo Giraudel wrote a post on using MJML in Rails.

Using Email Layouts

Note: Aleksandrs Ļedovskis kindly updated the gem for better Rails Email Layouts support - it should be a non-breaking change, but check the updated file naming below if you experience problems.


# mailers/my_mailer.rb
class MyMailer < ActionMailer::Base
  layout "default"

  def foo_bar(user)
    @recipient = user

    mail(to:, from: "") do |format|
      format.html # This will look for "default.html.erb" and then "default.html.mjml"

Note: If default.html.erb exists, email will be rendered as ERB, and MJML tags will not be compiled.

Email layout:

<!-- views/layouts/default.html.mjml -->
    <%= yield %>

Email view:

<!-- views/my_mailer/foo_bar.html.mjml (or foo_bar.html.erb) -->
<%= render partial: "to" %>

      Something foo regarding bar!

Email partial:

<!-- views/my_mailer/_to.html.mjml (or _to.html.erb) -->
      Hello <%= %>,

Sending Devise user emails

If you use Devise for user authentication and want to send user emails with MJML templates, here's how to override the devise mailer:

# app/mailers/devise_mailer.rb
class DeviseMailer < Devise::Mailer
  def reset_password_instructions(record, token, opts={})
    @token = token
    @resource = record
    # Custom logic to send the email with MJML
      template_path: 'devise/mailer',
      from: "",
      subject: "Custom subject"
    ) do |format|

Now tell devise to user your mailer in config/initializers/devise.rb by setting config.mailer = 'DeviseMailer' or whatever name you called yours.

And then your MJML template goes here: app/views/devise/mailer/reset_password_instructions.mjml

Devise also have more instructions if you need them.

Deploying with Heroku

To deploy with Heroku you'll need to setup multiple buildpacks so that Heroku first builds Node for MJML and then the Ruby environment for your app.

Once you've installed the Heroku Toolbelt you can setup the buildpacks from the commandline:

$ heroku buildpacks:set heroku/ruby

And then add the Node buildpack to index 1 so it's run first:

$ heroku buildpacks:add --index 1 heroku/nodejs

Check that's all setup by running:

$ heroku buildpacks

Next you'll need to setup a package.json file in the root, something like this:

  "name": "your-site",
  "version": "1.0.0",
  "description": "Now with MJML email templates!",
  "main": "index.js",
  "directories": {
    "doc": "doc",
    "test": "test"
  "dependencies": {
    "mjml": "^4.0.0"
  "repository": {
    "type": "git",
    "url": "git+"
  "keywords": [
  "author": "Your Name",
  "license": "ISC",
  "bugs": {
    "url": ""
  "homepage": ""

Then $ git push heroku master and it should Just WorkTM.

Bug reports

If you discover any bugs, feel free to create an issue on GitHub. Please add as much information as possible to help us fixing the possible bug. We also encourage you to help even more by forking and sending us a pull request.


Other similar gems


MIT License. Copyright 2018 Simon Loffler.

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MJML + ERb/Haml/Slim view template






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