SeleniumHQ/selenium · error · ArgumentError

Cannot use both :http_client and :client_config

Error message

Cannot use both :http_client and :client_config

What it means

A local driver accepts HTTP configuration through either an :http_client object or a :client_config object, but not both at once. They are alternative, mutually exclusive ways to configure the HTTP transport to the driver service. Passing both raises ArgumentError.

Solutions

  1. Choose one mechanism: pass only :http_client or only :client_config.
  2. If you need timeouts/URL settings, encode them in the ClientConfig and drop the http_client argument.
  3. If you have a custom HTTP client subclass, pass it via :http_client alone.

Example fix

# before
driver = Selenium::WebDriver.for(:chrome, http_client: client, client_config: config)

# after
driver = Selenium::WebDriver.for(:chrome, client_config: config)
Defensive patterns

Strategy: validation

Validate before calling

raise ArgumentError, 'pass either http_client or client_config, not both' if http_client && client_config

Try / catch

begin
  Selenium::WebDriver.for(:chrome, http_client: hc, client_config: cc)
rescue ArgumentError => e
  raise unless e.message.include?('http_client and :client_config')
  Selenium::WebDriver.for(:chrome, client_config: cc)
end

Prevention

When it happens

Trigger: Calling Selenium::WebDriver.for(:chrome, http_client: client, client_config: config). Building a ClientConfig for timeouts and also passing a custom Http::Default client.

Common situations: Gradually migrating from http_client-based configuration to client_config and leaving both in the hash. Merging two configuration sources without deduplication.

Related errors

AI-assisted analysis of SeleniumHQ/selenium@aa36b38e69 (2026-08-14). Data as JSON: /api/errors/00cd6bbdad329a3e. Report an issue: GitHub.

Appendix: source

Thrown at rb/lib/selenium/webdriver/common/local_driver.rb:65

        unless options.is_a?(default_options.class)
          raise ArgumentError, ":options must be an instance of #{default_options.class}"
        end

        finder = WebDriver::DriverFinder.new(options, service)
        options.binary = finder.browser_path if options.respond_to?(:binary) && finder.browser_path?
        service.executable_path = finder.driver_path
        options.browser_version = nil if options.respond_to?(:binary) && options.binary
        options.as_json
      end

      private

      def assert_local_arguments(url, http_client, client_config)
        if url || client_config&.server_url
          raise ArgumentError, "Can't set the server URL for #{self.class}; the service provides it"
        elsif http_client && client_config
          raise ArgumentError, 'Cannot use both :http_client and :client_config'
        end
      end
    end
  end
end

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