ActionVersionPreview

Preview multiple versions of your UI simultaneously using Rails' built-in view variants. No feature flags, no complex setup. Just create variant templates and visit them via URL.

Feature flag gems like Flipper are designed for toggling features on/off for users, not for showing multiple versions at once. For design iterations and feedback collection, you want to open three browser tabs side by side, each showing a different version, all logged in as the same user.

ActionVersionPreview makes this trivial using Rails' native view variants.

Read more about why I built this...

Add to your Gemfile:

gem "action_version_preview"

Run bundle install. That's it. The concern is automatically included in all controllers.

Rails looks for variant templates using this naming convention:

app/views/dashboard/show.html.erb           # default
app/views/dashboard/show.html+v2.erb        # variant :v2
app/views/dashboard/show.html+redesign.erb  # variant :redesign

This works for layouts, partials, mailers, and ViewComponent templates too.

/dashboard           # renders show.html.erb
/dashboard?vv=v2     # renders show.html+v2.erb
/dashboard?vv=true   # renders default, but activates the switcher

Drop the built-in switcher widget in your layout:

<%= variant_switcher %>

The switcher automatically detects available variants by scanning the view directory for +variant template files. It only appears when:

• The vv param is present in the URL (e.g., ?vv=true or ?vv=v2)
• The current action has variant templates available
• The user can preview variants (dev/test by default)

Standard Rails variants (mobile, tablet, phone, desktop) are excluded from detection.

Zero config is the default. But if you need to customize:

# config/initializers/action_version_preview.rb
ActionVersionPreview.configure do |config|
  # Change the URL parameter (default: :vv)
  config.param_name = :v

  # Control who can preview variants (default: dev/test only)
  # In production, you might want admins only:
  config.access_check = ->(controller) {
    Rails.env.development? ||
    Rails.env.test? ||
    controller.current_user&.admin?
  }
end

These are available in controllers and views:

Under the hood, ActionVersionPreview sets request.variant based on the URL parameter. Rails' template resolver then automatically looks for matching variant templates.

When you visit /dashboard?vv=v2:

1. The before_action extracts vv=v2 from params
2. It sets request.variant = :v2
3. Rails renders show.html+v2.erb instead of show.html.erb
4. The switcher detects all show.html+*.erb variants in the view directory

• Rails 7.0+ or 8.x
• Ruby 3.1+

MIT License. See MIT-LICENSE.