rails-css_unused is a static analysis gem that scans your stylesheets and all view files to report CSS classes that are defined but never used — no server required, no browser, pure file scanning.

bash bundle exec rake css_unused:report

v0.2.1 adds smart dynamic class variable detection — solving the most common false-positive in Rails apps where classes are assigned to a variable and rendered via ERB interpolation:

erb <% status_class = exam.approved? ? "status-approved" : "status-draft" %> <span class="<%= status_class %>">

The fix exploits a Ruby language rule: variable names cannot contain hyphens, so any hyphenated quoted string is unambiguously a string value. The scanner now extracts these automatically with no configuration needed.

Supports: ERB, HAML, Slim, ViewComponent, Phlex, Stimulus JS, BEM, CI exit codes.

• GitHub: https://github.com/sghani001/rails-css_unused
• RubyGems: https://rubygems.org/gems/rails-css_unused
• Full writeup on dev.to: https://dev.to/dev_syed_ghani/i-built-a-gem-that-finds-unused-css-classes-in-rails-apps-heres-the-interesting-problem-i-had-to-1acb