ViewComponent/view_component · error

WARNING: Template format for #{path} is missing, defaulting

Error message

WARNING: Template format for #{path} is missing, defaulting to :html.

What it means

Error "WARNING: Template format for #{path} is missing, defaulting to :html." thrown in ViewComponent/view_component.

Source

Thrown at lib/view_component/template.rb:27

    attr_reader :details, :path

    delegate :virtual_path, to: :@component
    delegate :format, :variant, to: :@details

    def initialize(component:, details:, lineno: nil, path: nil)
      @component = component
      @details = details
      @lineno = lineno
      @path = path
    end

    class File < Template
      def initialize(component:, details:, path:)
        # If the template file has no format (e.g. .erb instead of .html.erb),
        # assume the default format (html).
        if details.format.nil?
          Kernel.warn("WARNING: Template format for #{path} is missing, defaulting to :html.")
          details = ActionView::TemplateDetails.new(details.locale, details.handler, DEFAULT_FORMAT, details.variant)
        end

        super
      end

      def type
        :file
      end

      # Load file each time we look up #source in case the file has been modified
      def source
        ::File.read(@path)
      end

      private

      # Rails 8.1 added a newline to compiled ERB output (rails/rails#53731).

View on GitHub (pinned to 9f22c36fa7)

Solutions

1. Add an explicit format to the template file name, e.g. rename my_component.erb to my_component.html.erb.
2. If another format is intended, name the template accordingly, e.g. my_component.json.jbuilder.

When it happens

Trigger: Thrown at lib/view_component/template.rb:27 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of ViewComponent/view_component@9f22c36fa7 (2026-08-23). Data as JSON: /api/errors/0ac16280405f27e2. Report an issue: GitHub.