Slim is a template language whose goal is reduce the syntax to the essential parts without becoming cryptic.
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Slim is a template language whose goal is to reduce the view syntax to the essential parts without becoming cryptic. It started as an exercise to see how much could be removed from a standard html template (<, >, closing tags, etc...). As more people took an interest in Slim, the functionality grew and so did the flexibility of the syntax.

A short list of the features...

  • Elegant syntax
    • Short syntax without closing tags (Using indentation instead)
    • HTML style mode with closing tags
    • Configurable shortcut tags (# for <div id="..."> and . for <div class="..."> in the default configuration)
  • Safety
    • Automatic HTML escaping by default
    • Support for Rails' html_safe?
  • Highly configurable and extendable via plugins
    • Logic less mode similar to Mustache, realized as plugin
    • Translator/I18n, realized as plugin
  • High performance
    • Comparable speed to ERB/Erubis
    • Streaming support in Rails
  • Supported by all major frameworks (Rails, Sinatra, ...)
  • Full Unicode support for tags and attributes on Ruby 1.9
  • Embedded engines like Markdown and Textile


Upgrade to version 2.0

If you are already using Slim 1.x and want to upgrade to the newest version 2.0, you should at first upgrade to at least Slim 1.3.8 which will emit warnings for deprecated features. This way you can easily see if your application is already Slim 2.0 compliant!

Slim 2.0 removes deprecated features from the 1.3 series and cleans up some minor inconsistencies in the syntax (Attribute wrapper and quoted attribute escaping). Of course it also includes new features and bugfixes. See the CHANGES for details.

In general don't be afraid of upgrading! We try to be backward compatible and follow semantic versions as good as possible.


What is Slim?

Slim is a fast, lightweight templating engine with support for Rails 3 and 4. It has been heavily tested on all major ruby implementations. We use continuous integration (travis-ci).

Slim's core syntax is guided by one thought: "What's the minimum required to make this work".

As more people have contributed to Slim, there have been syntax additions influenced from their use of Haml and Jade. The Slim team is open to these additions because we know beauty is in the eye of the beholder.

Slim uses Temple for parsing/compilation and is also integrated into Tilt, so it can be used together with Sinatra or plain Rack.

The architecture of Temple is very flexible and allows the extension of the parsing and compilation process without monkey-patching. This is used by the logic less plugin and the translator plugin which provides I18n.

Why use Slim?

Within the Rails community, Erb and Haml are without doubt the two most popular templating engines. However, Erb's syntax is cumbersome and Haml's syntax can be quite cryptic to the uninitiated.

There is also some development in logic-less engines (e.g. Mustache which requires you to write standard HTML). You can also use Slim in logic-less mode if you like the Slim syntax to build your HTML but don't want to write Ruby in your templates.

Slim was born to bring a minimalist syntax approach with speed. If people chose not to use Slim, it would not be because of speed.

Yes, Slim is speedy! Benchmarks are done for every commit at!/slim-template/slim. Don't trust the numbers? That's as it should be. Please try the benchmark rake task yourself!

How to start?

Install Slim as a gem:

gem install slim

Include Slim in your Gemfile with gem 'slim' or require it with require 'slim'. That's it! Now, just use the .slim extension and you're good to go.

Syntax example

Here's a quick example to demonstrate what a Slim template looks like:

doctype html
    title Slim Examples
    meta name="keywords" content="template language"
    meta name="author" content=author
    link rel="icon" type="image/png" href=file_path("favicon.png")
      alert('Slim supports embedded javascript!')

    h1 Markup examples

      p This example shows you how a basic Slim file looks like.

    == yield

    - if items.any?
        - for item in items
            td.price = item.price
    - else
      p No items found Please add some inventory.
        Thank you!

    div id="footer"
      == render 'footer'
      | Copyright &copy; #{@year} #{@author}

Indentation matters, but the indentation depth can be chosen as you like. If you want to first indent 2 spaces, then 5 spaces, it's your choice. To nest markup you only need to indent by one space, the rest is gravy.

Line indicators

Text |

The pipe tells Slim to just copy the line. It essentially escapes any processing. Each following line that is indented greater than the pipe is copied over.

      This is a test of the text block.

The parsed result of the above:

<body><p>This is a test of the text block.</p></body>

The left margin is set at the indent of the pipe + one space. Any additional spaces will be copied over.

    | This line is on the left margin.
       This line will have one space in front of it.
         This line will have two spaces in front of it.
           And so on...

You can also embed html in the text line

- articles.each do |a|
  | <tr><td>#{}</td><td>#{a.description}</td></tr>

Text with trailing white space '

The single quote tells Slim to copy the line (similar to |), but makes sure that a single trailing white space is appended.

Inline html < (HTML style)

You can write html tags directly in Slim which allows you to write your templates in a more html like style with closing tags or mix html and Slim style.

    title Example
    - if articles.empty?
    - else
        - articles.each do |a|

Control code -

The dash denotes control code. Examples of control code are loops and conditionals. end is forbidden behind -. Blocks are defined only by indentation. If your ruby code needs to use multiple lines, append a backslash \ at the end of the lines. If your line ends with comma , (e.g because of a method call) you don't need the additional backslash before the linebreak.

  - if articles.empty?
    | No inventory

Output =

The equal sign tells Slim it's a Ruby call that produces output to add to the buffer. If your ruby code needs to use multiple lines, append a backslash \ at the end of the lines, for example:

= javascript_include_tag \

If your line ends with comma , (e.g because of a method call) you don't need the additional backslash before the linebreak. For trailing or leading whitespace the modifiers > and < are supported.

  • Output with trailing white space =>. Same as the single equal sign (=), except that it adds a trailing white space. The legacy syntax =' is also supported.
  • Output with leading white space =<. Same as the single equal sign (=), except that it adds a leading white space.

Output without HTML escaping ==

Same as the single equal sign (=), but does not go through the escape_html method. For trailing or leading whitespace the modifiers > and < are supported.

  • Output without HTML escaping and trailing white space ==>. Same as the double equal sign (==), except that it adds a trailing white space. The legacy syntax ==' is also supported.
  • Output without HTML escaping and leading white space ==<. Same as the double equal sign (==), except that it adds a leading white space.

Code comment /

Use the forward slash for code comments - anything after it won't get displayed in the final render. Use / for code comments and /! for html comments

    / This line won't get displayed.
      Neither does this line.
    /! This will get displayed as html comments.

The parsed result of the above:

<body><p><!--This will get displayed as html comments.--></p></body>

HTML comment /!

Use the forward slash immediately followed by an exclamation mark for html comments (<!-- ... -->).

IE conditional comment /[...]

/[if IE]
    p Get a better browser.

renders as

<!--[if IE]><p>Get a better browser.</p><![endif]-->

HTML tags

Doctype tag

The doctype tag is a special tag which can be used to generate the complex doctypes in a very simple way.


doctype xml
  <?xml version="1.0" encoding="utf-8" ?>

doctype xml ISO-8859-1
  <?xml version="1.0" encoding="iso-8859-1" ?>


doctype html
  <!DOCTYPE html>

doctype 5
  <!DOCTYPE html>

doctype 1.1
  <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN"

doctype strict
  <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"

doctype frameset
  <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Frameset//EN"

doctype mobile

doctype basic
  <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML Basic 1.1//EN"

doctype transitional
  <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"


doctype strict
  <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN"

doctype frameset
  <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Frameset//EN"

doctype transitional
  <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"

Closed tags (trailing /)

You can close tags explicitly by appending a trailing /.

img src="image.png"/

Note, that this is usually not necessary since the standard html tags (img, br, ...) are closed automatically.

Trailing and leading whitespace (<, >)

You can force Slim to add a trailing whitespace after a tag by adding a >.

a> href='url1' Link1
a> href='url2' Link2

You can add a leading whitespace by adding <.

a< href='url1' Link1
a< href='url2' Link2

You can also combine both.

a<> href='url1' Link1

Inline tags

Sometimes you may want to be a little more compact and inline the tags.

  li.first: a href="/a" A link
  li: a href="/b" B link

For readability, don't forget you can wrap the attributes.

  li.first: a[href="/a"] A link
  li: a[href="/b"] B link

Text content

Either start on the same line as the tag

  h1 id="headline" Welcome to my site.

Or nest it. You must use a pipe or an apostrophe to escape processing

  h1 id="headline"
    | Welcome to my site.

Dynamic content (= and ==)

Can make the call on the same line

  h1 id="headline" = page_headline

Or nest it.

  h1 id="headline"
    = page_headline


You write attributes directly after the tag. For normal text attributes you must use double " or single quotes ' (Quoted attributes).

a href="" title='Slim Homepage' Goto the Slim homepage

You can use text interpolation in the quoted attributes.

Attributes wrapper

If a delimiter makes the syntax more readable for you, you can use the characters {...}, (...), [...] to wrap the attributes.

  h1(id="logo") = page_logo
  h2[id="tagline" class="small tagline"] = page_tagline

If you wrap the attributes, you can spread them across multiple lines:

   class="small tagline"] = page_tagline

You may use spaces around the wrappers and assignments:

h1 id = "logo" = page_logo
h2 [ id = "tagline" ] = page_tagline

Quoted attributes


a href="" title='Slim Homepage' Goto the Slim homepage

You can use text interpolation in the quoted attributes:

a href="http://#{url}" Goto the #{url}

The attribute value will be escaped by default. Use == if you want to disable escaping in the attribute.

a href=="&amp;"

You can break quoted attributes with backslash \

a data-title="help" data-content="extremely long help text that goes on\
  and one and one and then starts over...."

Ruby attributes

Write the ruby code directly after the =. If the code contains spaces you have to wrap the code into parentheses (...). You can also directly write hashes {...} and arrays [...].

    - for user in users
      td id="user_#{}" class=user.role
        a href=user_action(user, :edit) Edit #{}
        a href=(path_to_user user) =

The attribute value will be escaped by default. Use == if you want to disable escaping in the attribute.

a href==action_path(:start)

You can also break ruby attributes with backslash \ or trailing , as describe for control sections.

Boolean attributes

The attribute values true, false and nil are interpreted as booleans. If you use the attribute wrapper you can omit the attribute assigment.

input type="text" disabled="disabled"
input type="text" disabled=true
input(type="text" disabled)

input type="text"
input type="text" disabled=false
input type="text" disabled=nil

Attribute merging

You can configure attributes to be merged if multiple are given (See option :merge_attrs). In the default configuration this is done for class attributes with the white space as delimiter. class="highlight" href=""

This renders as

<a class="menu highlight" href=""></a>

You can also use an Array as attribute value and the array elements will be merged using the delimiter.

a class=["menu","highlight"]
a class=:menu,:highlight

Splat attributes *

The splat shortcut allows you turn a hash in to attribute/value pairs

.card*{'data-url'=>place_path(place), 'data-id'=>} =

renders as

<div class="card" data-id="1234" data-url="/place/1234">Slim's house</div>

You can also use methods or instance variables which return a hash as shown here:

.card *method_which_returns_hash =
.card *@hash_instance_variable =

The hash attributes which support attribute merging (see Slim option :merge_attrs) can be given as an Array

.first *{:class => [:second, :third]} Text

renders as

div class="first second third"

Dynamic tags *

You can create completely dynamic tags using the splat attributes. Just create a method which returns a hash with the :tag key.

  def a_unless_current
    @page_current ? {:tag => 'span'} : {:tag => 'a', :href => ''}
- @page_current = true
*a_unless_current Link
- @page_current = false
*a_unless_current Link

renders as

<span>Link</span><a href="">Link</a>


Tag shortcuts

You can define custom tag shortcuts by setting the option :shortcut.

Slim::Engine.set_default_options :shortcut => {'c' => {:tag => 'container'}, '#' => {:attr => 'id'}, '.' => {:attr => 'class'} }

We can use it in Slim code like this

c.content Text

which renders to

<container class="content">Text</container>

Attribute shortcuts

You can define custom shortcuts (Similar to # for id and . for class).

In this example we add & to create a shortcut for the input elements with type attribute.

Slim::Engine.set_default_options :shortcut => {'&' => {:tag => 'input', :attr => 'type'}, '#' => {:attr => 'id'}, '.' => {:attr => 'class'}}

We can use it in Slim code like this

&text name="user"
&password name="pw"

which renders to

<input type="text" name="user" />
<input type="password" name="pw" />
<input type="submit" />

In another example we add @ to create a shortcut for the role attribute.

Slim::Engine.set_default_options :shortcut => {'@' => {:attr => 'role'}, '#' => {:attr => 'id'}, '.' => {:attr => 'class'}}

We can use it in Slim code like this

.person@admin =

which renders to

<div class="person" role="admin">Daniel</div>

You can also set multiple attributes at once using one shortcut.

Slim::Engine.set_default_options :shortcut => {'@' => {:attr => %w(data-role role)}}

We can use it in Slim code like this

.person@admin =

which renders to

<div class="person" role="admin" data-role="admin">Daniel</div>

ID shortcut # and class shortcut .

Similarly to Haml, you can specify the id and class attributes in the following shortcut form

    = page_headline
    = page_tagline
    = show_content

This is the same as

  h1 id="headline"
    = page_headline
  h2 id="tagline" class="small tagline"
    = page_tagline
  div class="content"
    = show_content

Helpers and capturing

If you use Slim you might want to extend your template with some helpers. Assume that you have the following helper

module Helpers
  def headline

which can be used in Slim as follows

  = headline do
    ' Hello

The content in the do block is then captured automatically and passed to the helper via yield. As a syntactic sugar you can omit the do keyword and write only

  = headline
    ' Hello

Text interpolation

Use standard Ruby interpolation. The text will be html escaped by default.

  h1 Welcome #{} to the show.
  | Unescaped #{{content}} is also possible.

To escape the interpolation (i.e. render as is)

  h1 Welcome \#{} to the show.

Embedded engines (Markdown, ...)

Thanks to Tilt, Slim has impressive support for embedding other template engines.


  square = (x) -> x * x

    Hello from #{"Markdown!"}
    Second Line!

Supported engines:

Filter Required gems Type Description
ruby: none Shortcut Shortcut to embed ruby code
javascript: none Shortcut Shortcut to embed javascript code and wrap in script tag
css: none Shortcut Shortcut to embed css code and wrap in style tag
sass: sass Compile time Embed sass code and wrap in style tag
scss: sass Compile time Embedd scss code and wrap in style tag
less: less Compile time Embed less css code and wrap in style tag
styl: styl Compile time Embed stylus css code and wrap in style tag
coffee: coffee-script Compile time Compile coffee script code and wrap in script tag
asciidoc: asciidoctor Compile time + Interpolation Compile AsciiDoc code and interpolate #{variables} in text
markdown: redcarpet/rdiscount/kramdown Compile time + Interpolation Compile markdown code and interpolate #{variables} in text
textile: redcloth Compile time + Interpolation Compile textile code and interpolate #{variables} in text
creole: creole Compile time + Interpolation Compile creole code and interpolate #{variables} in text
wiki:, mediawiki: wikicloth Compile time + Interpolation Compile wiki code and interpolate #{variables} in text
rdoc: rdoc Compile time + Interpolation Compile rdoc code and interpolate #{variables} in text
builder: builder Precompiled Embed builder code
nokogiri: nokogiri Precompiled Embed nokogiri builder code
erb: none Precompiled Embed erb code

The embedded engines can be configured in Slim by setting the options directly on the Slim::Embedded filter. Example:

Slim::Embedded.default_options[:markdown] = {:auto_ids => false}

Configuring Slim

Slim and the underlying Temple framework are highly configurable. The way how you configure Slim depends a bit on the compilation mechanism (Rails or Tilt). It is always possible to set default options per Slim::Engine class. This can be done in Rails' environment files. For instance, in config/environments/development.rb you probably want:

Default options

# Indent html for pretty debugging and do not sort attributes (Ruby 1.8)
Slim::Engine.set_default_options :pretty => true, :sort_attrs => false

# Indent html for pretty debugging and do not sort attributes (Ruby 1.9)
Slim::Engine.set_default_options pretty: true, sort_attrs: false

You can also access the option hash directly:

Slim::Engine.default_options[:pretty] = true

Setting options at runtime

There are two ways to set options at runtime. For Tilt templates (Slim::Template) you can set the options when you instatiate the template:'template.slim', optional_option_hash).render(scope)

The other possibility is to set the options per thread which is interesting mostly for Rails:

Slim::Engine.with_options(option_hash) do
   # Any Slim engines which are created here use the option_hash
   # For example in Rails:
   render :page, :layout => true

You have to be aware that the compiled engine code and the options are cached per template in Rails and you cannot change the option afterwards.

# First render call
Slim::Engine.with_options(:pretty => true) do
   render :page, :layout => true

# Second render call
Slim::Engine.with_options(:pretty => false) do
   render :page, :layout => true # :pretty is still true because it is cached

Available options

The following options are exposed by the Slim::Engine and can be set with Slim::Engine.set_default_options. There are a lot of them but the good thing is, that Slim checks the configuration keys and reports an error if you try to use an invalid configuration key.

Type Name Default Purpose
String :file nil Name of parsed file, set automatically by Slim::Template
Integer :tabsize 4 Number of white spaces per tab (used by the parser)
String :encoding "utf-8" Set encoding of template
String :default_tag "div" Default tag to be used if tag name is omitted
Hash :shortcut {'.' => {:attr => 'class'}, '#' => {:attr => 'id'}} Attribute shortcuts
Array<Symbol,String> :enable_engines nil (All enabled) List of enabled embedded engines (whitelist)
Array<Symbol,String> :disable_engines nil (None disabled) List of disabled embedded engines (blacklist)
Boolean :disable_capture false (true in Rails) Disable capturing in blocks (blocks write to the default buffer
Boolean :disable_escape false Disable automatic escaping of strings
Boolean :use_html_safe false (true in Rails) Use String#html_safe? from ActiveSupport (Works together with :disable_escape)
Symbol :format :xhtml HTML output format (Possible formats :xhtml, :html4, :html5, :html)
String :attr_quote '"' Character to wrap attributes in html (can be ' or ")
Hash :merge_attrs {'class' => ' '} Joining character used if multiple html attributes are supplied (e.g. class="class1 class2")
Array<String> :hyphen_attrs %w(data) Attributes which will be hyphenated if a Hash is given (e.g. data={a:1,b:2} will render as data-a="1" data-b="2")
Boolean :sort_attrs true Sort attributes by name
Symbol :js_wrapper nil Wrap javascript by :comment, :cdata or :both. You can also :guess the wrapper based on :format.
Boolean :pretty false Pretty HTML indenting, only block level tags are indented (This is slower!)
String :indent ' ' Indentation string
Boolean :streaming false (true in Rails > 3.1) Enable output streaming
Class :generator Temple::Generators::ArrayBuffer/ RailsOutputBuffer Temple code generator (default generator generates array buffer)
String :buffer '_buf' ('@output_buffer' in Rails) Variable used for buffer

There are more options which are supported by the Temple filters but which are not exposed and are not officially supported. You have to take a look at the Slim and Temple code for that.

Option priority and inheritance

For developers who know more about Slim and Temple architecture it is possible to override default options at different positions. Temple uses an inheritance mechanism to allow subclasses to override options of the superclass. The option priorities are as follows:

  1. Slim::Template options passed at engine instatination
  2. Slim::Template.default_options
  3. Slim::Engine.thread_options, Slim::Engine.default_options
  4. Parser/Filter/Generator thread_options, default_options (e.g Slim::Parser, Slim::Compiler)

It is also possible to set options for superclasses like Temple::Engine. But this will affect all temple template engines then.

Slim::Engine < Temple::Engine
Slim::Compiler < Temple::Filter


Slim currently provides plugins for logic less mode and I18n. See the plugin documentation.

Framework support


Slim uses Tilt to compile the generated code. If you want to use the Slim template directly, you can use the Tilt interface.['template.slim'].render(scope)'template.slim', optional_option_hash).render(scope) { source }.render(scope)

The optional option hash can have to options which were documented in the section above.


require 'sinatra'
require 'slim'

get('/') { slim :index }

@@ index
doctype html
    title Sinatra With Slim
    h1 Slim Is Fun!


Rails generators are provided by slim-rails. slim-rails is not necessary to use Slim in Rails though. Just install Slim and add it to your Gemfile with gem 'slim'. Then just use the .slim extension and you're good to go.


HTTP streaming is enabled by default if you use a Rails version which supports it.


Slim Command 'slimrb'

The gem 'slim' comes with the small tool 'slimrb' to test Slim from the command line.

$ slimrb --help
Usage: slimrb [options]
    -s, --stdin                      Read input from standard input instead of an input file
        --trace                      Show a full traceback on error
    -c, --compile                    Compile only but do not run
    -e, --erb                        Convert to ERB
    -r, --rails                      Generate rails compatible code (Implies --compile)
    -t, --translator                 Enable translator plugin
    -l, --logic-less                 Enable logic less plugin
    -p, --pretty                     Produce pretty html
    -o, --option [NAME=CODE]         Set slim option
    -h, --help                       Show this message
    -v, --version                    Print version

Start 'slimrb', type your code and press Ctrl-d to send EOF. Example usage:

$ slimrb
  First paragraph.

  Second paragraph.

  * one
  * two
  * three

//Enter Ctrl-d
<p>First paragraph </p>

<p>Second paragraph </p>


Syntax Highlighters

There are plugins for various text editors (including the most important ones - Vim, Emacs and Textmate):

Template Converters (HAML, ERB, ...)



Yes, Slim is one of the fastest Ruby template engines out there! In production mode Slim is nearly as fast as Erubis (which is the fastest template engine). But we would be happy if you chose Slim also for any other reason, we assure you performance will not be an obstacle.

Run the benchmarks with rake bench. You can add the option slow to run the slow parsing benchmark which needs more time. You can also increase the number of iterations.

rake bench slow=1 iterations=1000

We run the benchmarks for every commit on Travis-CI. Take a look at the newest benchmarking results:!/slim-template/slim

Test suite and continuous integration

Slim provides an extensive test-suite based on minitest. You can run the tests with 'rake test' and the rails integration tests with 'rake test:rails'.

We are currently experimenting with human-readable literate tests which are written as markdown files:

Travis-CI is used for continuous integration testing:!/slim-template/slim

Slim is working well on all major Ruby implementations:

  • Ruby 2.0.0
  • Ruby 1.8.7
  • Ruby 1.9.2
  • Ruby 1.9.3
  • Ruby EE
  • JRuby
  • Rubinius 2.0


If you'd like to help improve Slim, clone the project with Git by running:

$ git clone git://

Work your magic and then submit a pull request. We love pull requests!

Please remember to test against Ruby versions 2.0.0, 1.9.3 and 1.8.7.

If you find the documentation lacking, help us out and update this If you don't have the time to work on Slim, but found something we should know about, please submit an issue.


Slim is released under the MIT license.



Related projects

Template compilation framework:

Framework support:

Syntax highlighting:

Template Converters (HAML, ERB, ...):

Language ports/Similar languages: