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.

Why?

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...

Installation

Add to your Gemfile:

gem "action_version_preview"

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

Usage

1. Create Variant Templates

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.

2. Visit the Variant URL

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

3. Add the Variant Switcher (Optional)

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.

Configuration

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

Helper Methods

These are available in controllers and views:

Method	Description
current_variant	Returns the active variant symbol (e.g., :v2) or nil
detected_variants	Returns array of variant names found for current action
variant_preview_active?	Returns true if variant preview mode is active
can_preview_variants?	Returns true if current user can access variants
variant_switcher	Renders the switcher widget

How It Works

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

Comparison: Feature Flags vs View Variants

Feature Flags (Flipper)	View Variants (This Gem)
Toggle features on/off for users	Access all versions simultaneously
One version "live" at a time	Side-by-side comparison in multiple tabs
Percentage rollouts, A/B testing	Design iteration, feedback collection
Requires database/Redis	Zero dependencies

Requirements

• Rails 7.0+ or 8.x
• Ruby 3.1+

License

MIT License. See MIT-LICENSE.