https://github.com/premailer/premailer
Preflight for HTML email
https://github.com/premailer/premailer
css inline mail nokogiri premailer ruby
Last synced: 6 months ago
JSON representation
Preflight for HTML email
- Host: GitHub
- URL: https://github.com/premailer/premailer
- Owner: premailer
- License: other
- Created: 2009-11-26T05:31:46.000Z (almost 16 years ago)
- Default Branch: master
- Last Pushed: 2025-04-01T16:27:23.000Z (8 months ago)
- Last Synced: 2025-05-06T16:12:09.530Z (7 months ago)
- Topics: css, inline, mail, nokogiri, premailer, ruby
- Language: Ruby
- Homepage: https://premailer.github.io/premailer
- Size: 1.01 MB
- Stars: 2,364
- Watchers: 57
- Forks: 365
- Open Issues: 97
-
Metadata Files:
- Readme: README.md
- Changelog: CHANGELOG.md
- License: LICENSE.md
Awesome Lists containing this project
- awesome-email-marketing - Premailer
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README
# Premailer README [](https://github.com/premailer/premailer/actions/workflows/actions.yml) [](https://badge.fury.io/rb/premailer)
## 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
gem is a 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](#plain-text-version) is created (optional)
## Installation
```bash
gem install premailer
```
## Example
```ruby
require 'premailer'
premailer = Premailer.new('http://example.com/myfile.html', warn_level: Premailer::Warnings::SAFE)
# Write the plain-text output (must come before to_inline_css)
File.write "output.txt", premailer.to_plain_text
# Write the HTML output
File.write "output.html", 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]}"
end
```
## Adapters
1. nokogiri (default)
2. nokogiri_fast (20x speed, more memory)
3. nokogumbo
(hpricot adapter removed, use `~>1.9.0` version if you need it)
Picking an adapter:
```ruby
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
```css
table { -premailer-cellspacing: 5; -premailer-width: 500; }
```
will result in
```html
```
## Plain text version
Premailer can generate a plain text version of your HTML. Links and images will be inlined.
For example
```html
```
will become
```text
Premailer Logo ( https://example.com )
```
To ignore/omit a section of HTML content from the plain text version, wrap it with the following comments.
```html
This will be omitted from the plain text version.
This is extremely helpful for removing email headers and footers
that aren't needed in the text version.
```
## Configuration options
For example:
```ruby
Premailer.new(
html, # html as string
with_html_string: true,
drop_unmergeable_css_rules: true
)
```
[available options](https://premailer.github.io/premailer/Premailer.html#initialize-instance_method)
## Support for CSS variables
The gem does not automatically replace CSS variables with their static values.
For example, if a variable is used to set the `font-weight` of an `h1` element, the result will be
```html
Title
```
This causes the `font-weight` value to be the CSS variable call `var(--bulma-content-heading-weight);` instead of its static value.
### Replace CSS variable calls with their static values
The following section instructs how to replace CSS variables with their static value in the context of a Ruby on Rails application.
Install the `postcss-css-variables` plugin for PostCSS to process the CSS variables.
```shell
yarn add postcss postcss-cli postcss-css-variables
```
To configure the plugin, create the file `postcss.config.js` in the root directory with the content:
```javascript
module.exports = {
plugins: [
// https://github.com/MadLittleMods/postcss-css-variables to transform the css
require("postcss-css-variables")({
preserve: false, // Set to false to replace variables with static values
}),
],
};
```
In the `package.json` file, add the new "build:emails" to the scripts.
Replace `./app/assets/stylesheets/emails.css` with your file path:
```json
"scripts": {
"build:emails": "postcss ./app/assets/stylesheets/emails.css -o ./app/assets/builds/emails.css"
}
```
The previous script processes and overwrites the file at `./app/assets/stylesheets/emails.css` with PostCSS using its `postcss-css-variables` plugin, replacing the CSS variables with their static value.
If the file to be processed is not `.css`, but `.scss`, it needs to be converted first to `.css`, then have its variables replaced. The script would then be
```json
"scripts": {
"build:emails": "sass ./app/assets/stylesheets/emails.scss:./app/assets/builds/emails.css --no-source-map --load-path=node_modules && postcss ./app/assets/builds/emails.css -o ./app/assets/builds/emails.css"
}
```
Next, to execute the script when running `bin/dev`, add the following line in the file `Procfile.dev`
```
emails_css: yarn build:emails --watch
```
The srcipt can also be executed separately with the command
```shell
yarn build:emails
```
### Caveat
The variables must be declared before use. Otherwise, their values when called will be set to `undefined`.
## Contributions
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.
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](https://github.com/premailer/premailer/contributors) for their updates.
Thanks to [Greenhood + Company](http://www.greenhood.com/) for sponsoring some of the 1.5.6 updates,
and to [Campaign Monitor](https://www.campaignmonitor.com/) for supporting the web interface.
The source code can be found on [GitHub](https://github.com/premailer/premailer).
Copyright by Alex Dunae (dunae.ca, e-mail 'code' at the same domain), 2007-2017. See [LICENSE.md](https://github.com/premailer/premailer/blob/master/LICENSE.md) for license details.