MJML + ERb/Haml/Slim view template
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MJML-Rails allows you to render HTML e-mails from an MJML template.

An example template might look like:

<!-- ./app/views/user_mailer/email.html.mjml -->
    <mj-preview>Hello World</mj-preview>
        <mj-text>Hello World</mj-text>
        <%= render partial: "info" %>

And the partial _info.mjml:

<!-- ./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: "user@example.com", from: "app@example.com") do |format|


Add it to your Gemfile.

gem 'mjml-rails'

Run the following command to install it:

bundle install

Install the MJML parser (optional -g to install it globally):

npm install -g mjml

Note that you'll need at least Node.js version 6 for MJML to function properly.

If you're using :haml or any other Rails template language, create an initializer to set it up:

# config/initializers/mjml.rb
Mjml.setup do |config|
  config.template_language = :erb # :erb (default), :slim, :haml, or any other you are using

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

If you'd like to see render errors:

Mjml.setup do |config|
  # Default is `false` (errors suppressed), set to `true` to enable error raising
  config.raise_render_exception = true

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: user.email, from: "app@example.com") do |format|

Email layout:

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

Email view:

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

      Something foo regarding bar!

Email partial:

<!-- views/my_mailer/_to.html.erb -->
      Hello <%= @recipient.name %>,

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: "some@email.com",
      to: record.email,
      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+https://github.com/your-repo/your-site.git"
  "keywords": [
  "author": "Your Name",
  "license": "ISC",
  "bugs": {
    "url": "https://github.com/sighmon/mjml-rails/issues"
  "homepage": "https://github.com/sighmon/mjml-rails"

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.



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MIT License. Copyright 2018 Simon Loffler. sighmon.com

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