SeleniumHQ/selenium · error · Error::WebDriverError

could not find extension at #{path.inspect}

Error message

could not find extension at #{path.inspect}

What it means

Chromium Options#add_extension validates the path before queuing it for Base64 encoding on session creation. It raises Error::WebDriverError if no regular file exists at the given path (File.file? is false). A separate check then requires the .crx extension. Only real .crx files are accepted.

Source

Thrown at rb/lib/selenium/webdriver/chromium/options.rb:253

            options['args'] ||= []
            options['args'] << "--user-data-dir=#{@profile.directory}"
          end

          return if (@encoded_extensions + @extensions).empty?

          options['extensions'] = @encoded_extensions + @extensions.map { |ext| encode_extension(ext) }
        end

        def binary_path
          Chrome.path
        end

        def encode_extension(path)
          File.open(path, 'rb') { |crx_file| Base64.strict_encode64 crx_file.read }
        end

        def validate_extension(path)
          raise Error::WebDriverError, "could not find extension at #{path.inspect}" unless File.file?(path)
          raise Error::WebDriverError, "file was not an extension #{path.inspect}" unless File.extname(path) == '.crx'

          @extensions << path
        end

        def camelize?(key)
          !%w[localState prefs].include?(key)
        end
      end # Options
    end # Chromium
  end # WebDriver
end # Selenium

View on GitHub (pinned to aa36b38e69)

Solutions

1. Use an absolute path to the .crx file: options.add_extension(File.expand_path('ext.crx', __dir__)).
2. Verify File.file?(path) before calling, and that the extension is .crx.
3. Ensure the .crx is packaged with your app/gem and deployed to the runtime environment.
4. Prefer add_encoded_extension with a pre-encoded Base64 string if the file location varies.

Example fix

// before
options.add_extension('vendor/ext.crx')
// after
options.add_extension(File.expand_path('vendor/ext.crx', __dir__))

def crx_file?(path)
  File.file?(path) && File.extname(path) == '.crx'
end

raise 'not a .crx file' unless crx_file?(path)
options.add_extension(path)

def valid_extension_path?(path)
  File.file?(path) && File.extname(path).casecmp?('.crx')
end

begin
  options.add_extension(path)
rescue Selenium::WebDriver::Error::WebDriverError => e
  raise unless e.message =~ /could not find extension/
  options.add_extension(File.expand_path('ext.crx', __dir__))
end

When it happens

Trigger: Calling options.add_extension('/path/to/ext') where the path does not exist, points to a directory, or is otherwise not a regular file.

Common situations: Relative path resolved against the wrong working directory, packaging the gem without bundling the .crx, typo in the path, file deleted between runs, CI running from a different cwd than local.

Related errors

• Path to the extension doesn't exist
• could not find extension at #{path.inspect}
• argument can not be null
• Binary Location Must be a String
• :options must be an instance of #{default_options.class}

AI-assisted analysis of SeleniumHQ/selenium@aa36b38e69 (2026-08-14). Data as JSON: /api/errors/6ca0199af7cde25d. Report an issue: GitHub.