Streamlined Syntax - Unveiling the Power of Slim Template Language

railsApril 03, 2024Dotby Alkesh Ghorpade


In Ruby programming, developers always look for tools and frameworks that help them build applications efficiently without sacrificing performance or elegance. One such tool that has gained significant popularity is Slim Gem. Slim is a lightweight templating engine for Ruby that allows developers to write clean and concise markup without the verbosity often associated with traditional templating languages.

What is Slim Gem?

Slim is a templating language for Ruby that aims to minimize the typing required to create HTML markup while maintaining readability and expressiveness.

Slim achieves its goal of reducing verbosity by using indentation-based syntax and minimal punctuation. This makes Slim templates extremely clean and easy to read, with a syntax resembling plain HTML.

How Does Slim Gem Work?

Slim templates are written in plain text files with a ".slim" extension. These files contain a combination of HTML-like markup and Ruby code, allowing developers to embed dynamic content seamlessly within their markup.

One of the critical features of Slim is its use of indentation to define the document's structure. Unlike HTML or ERB, which rely on opening and closing tags, Slim uses indentation to indicate nesting levels. This results in code that is more visually appealing and easier to understand.

For example, here's a simple Slim template that generates a basic HTML page:

doctype html
    title Slim Gem Example
    h1 Hello, World!
    p Welcome to Slim Gem.

Getting Started with Slim

Integrating Slim into your Rails project is a breeze. Add the slim gem to your Gemfile and execute the bundle install command.

gem 'slim'

Use the .slim extension on your view files, and you're ready.

Here's a simple Slim template that generates a basic HTML page:

doctype html
    title Slim Gem Example
      alert('Slim Gem')

    h1 Hello, World!

      p Welcome to Slim Gem.

In this example, each indentation level represents a nested element in the HTML document. This makes it easy to see the document's structure at a glance without having to parse through a maze of opening and closing tags.

To include blocks of text without any processing or interpretation, you need to use the pipe |.

      This is a verbatim text block.

The parsed result of the above code block is

<body><p>This is a verbatim text block.</p></body>

To add loops in slim view, you need to dash -. The dash denotes control code.

  - @posts.each do |post|
      = link_to post.title, post_path(post)
      p = truncate(post.body, length: 100)

Similar to loops, for conditions you need to use the dash - as below.

- if current_user.admin?
  p You are an admin user.
- else
  p You are a regular user.

The equals sign (=) indicates that following code is a Ruby expression that generates output. This output is then added to the final HTML content. If your Ruby code spans multiple lines, you can use a backslash (\) at the end of each line to signal continuation.

= javascript_include_tag \

Text interpolation in Slim allows you to seamlessly integrate Ruby code within your templates to generate dynamic content.

  h1 Hi #{}
  | Welcome #{{text}}.

With slim, you can also generate dynamic tags based on conditions.

- if condition
  - tag_name = "h1"
- else
  - tag_name = "h2"

  - # Render a dynamic tag based on the value of the tag_name variable
  #{tag_name} Welcome to our website!

Why Choose Slim Gem?

There are several reasons why developers might choose Slim Gem for their Ruby projects:

  • Clean and Concise Syntax: Slim's indentation-based syntax makes it easy to write and understand markup, resulting in cleaner and more maintainable code.

  • Lightweight: Slim Gem is extremely lightweight, with minimal dependencies and overhead. This makes it ideal for applications where performance is a priority.

  • Integrates Seamlessly with Ruby: Since Slim templates are just plain text files with embedded Ruby code, they integrate seamlessly with Ruby applications. This makes it easy to pass data from the backend to the frontend and vice versa.

  • Active Community and Ecosystem: Slim Gem has a vibrant community of developers who contribute plugins, extensions, and tutorials to help others get started with the framework. This ensures that developers have access to a wealth of resources and support when using Slim in their projects.


Slim Gem is a powerful and elegant templating engine for Ruby that offers a clean and concise syntax for writing HTML markup. Its lightweight nature, seamless integration with Ruby, and active community make it an excellent choice for developers looking to build elegant and performant applications. Whether building a simple website or a complex web application, Slim Gem provides the tools you need to do the job efficiently and effectively.

Closing Remark

Could your team use some help with topics like this and others covered by ShakaCode's blog and open source? We specialize in optimizing Rails applications, especially those with advanced JavaScript frontends, like React. We can also help you optimize your CI processes with lower costs and faster, more reliable tests. Scraping web data and lowering infrastructure costs are two other areas of specialization. Feel free to reach out to ShakaCode's CEO, Justin Gordon, at or schedule an appointment to discuss how ShakaCode can help your project!
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