index.json.jbuilder

json.products @products do |product|
  json.(product, :id, :price, :permalink)
end

products_controller.rb

def index
  taxon = Spree::Taxon.where(permalink: params[:taxon]).first
  raise InvalidTaxon if taxon.blank? || params[:taxon].match('swatch')

  @products = SizeFilterService.new(taxon, params).filter!

end

show.json.jbuilder

Jbuilder.encode do |json|
  json.(@product, :id, :name, :sku, :description, :price)

  json.permalink @product.slug
  json.in_stock @product.in_stock?
  json.collection @product.collection.name.titelize if @product.collection.present?

  json.images @product.images do |image|
    json.original_image_url image.attachment.url(:original)
    json.image_url image.attachment.url(:product_medium)
    json.large_image_url image.attachment.url(:large)
    json.mini_image_url image.attachment.url(:mini)
  end

  json.variants @product.variants do |variant|
    json.(variant, :sku, :id, :product_id)
    json.in_stock variant.in_stock?
  end
end