Slim
Slim: A focused Ruby templating engine for teams that prefer concise, indentation-based markup. Ranked #39 of 65 in Template Engine Software by our editors (5.6/10); pricing: Free plan; best for ruby teams preferring indentation-based markup.
At a glance
- Editor score5.6 / 10
- PricingFree plan
- Best forRuby teams preferring indentation-based markup
- Free planYes
- Paid fromFree
- Rendering modeServer
- Facts checked23 Oct 2026
Where it wins
- Indentation-based syntax avoids required closing tags.
- Escapes HTML by default and supports Ruby expressions and control flow.
- Works with Rails, Sinatra, Rack, and Tilt; supports partials and embedded engines.
Where it doesn't
- Its specialized syntax may not suit teams preferring conventional HTML templates.
- Ruby expressions and control flow make it less suited to logic-less templating.
- It is a self-hosted library rather than a hosted subscription product.
Our verdict on Slim
Slim is a Ruby template language and engine for generating markup in web views. Its indentation-based syntax avoids required closing tags, making it a fit for Ruby teams that want concise templates and are comfortable with a distinct markup style. Templates can use Ruby expressions and control flow, and HTML output is escaped by default. Slim is distributed as a Ruby gem under the MIT license, rather than as a hosted subscription service.
The main appeal is its combination of markup authoring and Ruby-side rendering features. Templates can include other templates and render partials, and embedding engines such as Markdown, Sass, and JavaScript extends what a view can express. A logic-less mode is also available through a plugin for teams that want to limit template logic. Rails streaming support is included, and integrations with Rails, Sinatra, Rack, and Tilt give Ruby developers several ways to fit Slim into an application stack.
Slim's focus is also its main trade-off: teams need to choose and maintain a specialized indentation-based syntax, and Ruby expressions and control flow may be a poor fit for projects seeking strictly logic-less templates. It is self-hosted, so it suits teams selecting a Ruby library for their own application rather than buyers looking for a managed template service. Choose Slim when concise Ruby templates, escaping, partials, and embedded engines are useful; consider another approach if conventional HTML syntax or a hosted product is a requirement.
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Slim pricing
Slim fact sheet
| Free plan | Yes |
|---|---|
| Paid from | Free |
| Rendering mode | Server |
| Syntax model | Logic-based |
| Template inheritance | Not verified |
| Automatic escaping | Yes |
| Sandbox mode | Not verified |
| Async rendering | Not verified |
| License model | Open-source |
| Deployment | Self-hosted |
| Built for | Solo, Small business, Mid-market, Enterprise (editorial estimate) |
| Integrations | 4 integrations: Rails, Sinatra, Rack, Tilt |
| Pricing | Free plan |
| Website | slim-template.github.io |
| Facts checked | 23 Oct 2026 |
Slim integrations
Slim lists 4 integrations on its own site.
- Rails
- Sinatra
- Rack
- Tilt
Alternatives to Slim
- JinjaJinja gives Python applications inheritance, configurable rendering, and compilation in an open-source engine.9.4
- TwigA free, open-source PHP engine for compiled templates, inheritance, escaping, and sandboxing.9.3
- Handlebars.jsA free, open-source template engine for JavaScript projects that need reusable HTML.9.2
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Reviewed by iTechGuides Editors · Editorial team · Updated Oct 2026
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