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Premailer README CI Gem Version

What is this?

For the best HTML e-mail delivery results, CSS should be inline. This is a huge pain and a simple newsletter becomes un-managable very quickly. This script is my solution.

  • CSS styles are converted to inline style attributes
    • Checks style and link[rel=stylesheet] tags and preserves existing inline attributes
  • Relative paths are converted to absolute paths
    • Checks links in href, src and CSS url('')
  • CSS properties are checked against e-mail client capabilities
    • Based on the Email Standards Project's guides
  • A plain text version is created (optional)


Install the Premailer gem from RubyGems.

gem install premailer

or add it to your Gemfile and run bundle.


require 'premailer'

premailer ='', :warn_level => Premailer::Warnings::SAFE)

# Write the plain-text output
# This must come before to_inline_css ("output.txt", "w") do |fout|
  fout.puts premailer.to_plain_text

# Write the HTML output"output.html", "w") do |fout|
  fout.puts premailer.to_inline_css

# Output any CSS warnings
premailer.warnings.each do |w|
  puts "#{w[:message]} (#{w[:level]}) may not render properly in #{w[:clients]}"


Premailer's default adapter is nokogiri if both nokogiri and nokogumbo are included in the Gemfile list. However, if you want to use a different adapter, you can choose to.

There are three adapters in total (as of premailer 1.10.0)

  1. nokogiri (default)
  2. nokogiri_fast
  3. nokogumbo

hpricot adapter removed due to its EOL, please use ~>1.9.0 version if You still need it..

NokogiriFast adapter improves the Algorithmic complexity of the running time by 20x with a slight compensation on memory. To switch to any of these adapters, add the following line. For example, if you want to include the NokogiriFast adapter,

Premailer::Adapter.use = :nokogiri_fast

Ruby Compatibility

See .github/workflows/actions.yml for which ruby versions are tested. JRuby support is close, contributors are welcome.

Premailer-specific CSS

Premailer looks for a few CSS attributes that make working with tables a bit easier.

CSS Attribute Availability
-premailer-width Available on table, th and td elements
-premailer-height Available on table, tr, th and td elements
-premailer-cellpadding Available on table elements
-premailer-cellspacing Available on table elements
-premailer-align Available on table elements
data-premailer="ignore" Available on link and style elements. Premailer will ignore these elements entirely.

Each of these CSS declarations will be copied to appropriate element's attribute.

For example

table { -premailer-cellspacing: 5; -premailer-width: 500; }

will result in

<table cellspacing='5' width='500'>

Configuration options

The behavior of Premailer can be configured by passing options in the initializer.

For example, the following will accept HTML from a string and will exclude unmergeable css from being added to the <head> of the output document.

premailer =, with_html_string: true, drop_unmergeable_css_rules: true)

See here for a full list of the available options.


Contributions are most welcome. Premailer was rotting away in a private SVN repository for too long and could use some TLC. Fork and patch to your heart's content. Please don't increment the version numbers, though.

A few areas that are particularly in need of love:

  • Improved test coverage
  • Move un-repeated background images defined in CSS for Outlook

Credits and code

Thanks to all the wonderful contributors for their updates.

Thanks to Greenhood + Company for sponsoring some of the 1.5.6 updates, and to Campaign Monitor for supporting the web interface.

The source code can be found on GitHub.

Copyright by Alex Dunae (, e-mail 'code' at the same domain), 2007-2017. See for license details.