SeleniumHQ/selenium · error · WebDriverException

Can't get debugger address.

Error message

Can't get debugger address.

What it means

Raised by _get_cdp_details() when reading the debugger address from goog:chromeOptions (Chrome) or ms:edgeOptions (Edge) raises AttributeError — i.e. the options capability is None or otherwise lacks a .get method. The method expects a dict with a 'debuggerAddress' key; if the browser-specific options cap is missing or null, .get('debuggerAddress') on None blows up and is caught here.

Source

Thrown at py/selenium/webdriver/remote/webdriver.py:1450

        if self._request is None:
            from selenium.webdriver.common.api_request_context import APIRequestContext

            self._request = APIRequestContext(self)
        return self._request

    def _get_cdp_details(self):
        import json

        import urllib3

        http = urllib3.PoolManager()
        try:
            if self.caps.get("browserName") == "chrome":
                debugger_address = self.caps.get("goog:chromeOptions").get("debuggerAddress")
            elif self.caps.get("browserName") in ("MicrosoftEdge", "webview2"):
                debugger_address = self.caps.get("ms:edgeOptions").get("debuggerAddress")
        except AttributeError:
            raise WebDriverException("Can't get debugger address.")

        res = http.request("GET", f"http://{debugger_address}/json/version")
        data = json.loads(res.data)

        browser_version = data.get("Browser")
        websocket_url = data.get("webSocketDebuggerUrl")

        import re

        version = re.search(r".*/(\d+)\.", browser_version).group(1)

        return version, websocket_url

    # Virtual Authenticator Methods
    def add_virtual_authenticator(self, options: VirtualAuthenticatorOptions) -> None:
        """Adds a virtual authenticator with the given options.

        Example:

View on GitHub (pinned to aa36b38e69)

Solutions

  1. Ensure the browser reports goog:chromeOptions / ms:edgeOptions with a debuggerAddress (launch with --remote-debugging-port).
  2. Use Selenium Grid which injects se:cdp/se:cdpVersion so _get_cdp_details() is not needed.
  3. If constructing caps manually, include the options dict with a valid debuggerAddress.
Defensive patterns

Strategy: validation

Validate before calling

browser = driver.capabilities.get('browserName')
opts_key = 'goog:chromeOptions' if browser == 'chrome' else 'ms:edgeOptions'
opts = driver.capabilities.get(opts_key) or {}
if not isinstance(opts, dict) or not opts.get('debuggerAddress'):
    raise RuntimeError(f'{opts_key} missing debuggerAddress; launch with --remote-debugging-port')

Type guard

def has_debugger_address(driver) -> bool:
    browser = driver.capabilities.get('browserName')
    key = 'goog:chromeOptions' if browser == 'chrome' else 'ms:edgeOptions'
    opts = driver.capabilities.get(key)
    return isinstance(opts, dict) and bool(opts.get('debuggerAddress'))

Try / catch

from selenium.common.exceptions import WebDriverException
try:
    driver.start_devtools()
except WebDriverException as e:
    if "Can't get debugger address" in str(e):
        raise

Prevention

When it happens

Trigger: Calling start_devtools()/bidi_connection() (which fall back to _get_cdp_details() when se:cdp is absent) on a Chrome/Edge session whose goog:chromeOptions or ms:edgeOptions capability is None or absent. The browserName matches 'chrome' or ('MicrosoftEdge'/'webview2') but the options dict is null.

Common situations: A remote/Grid that strips the vendor options caps, a manually-constructed capabilities dict that omits goog:chromeOptions, or a Chromium-based browser that does not report debuggerAddress. Note: for a browserName that is neither chrome nor edge, debugger_address is never assigned and you get a downstream NameError, not this message.

Related errors

AI-assisted analysis of SeleniumHQ/selenium@aa36b38e69 (2026-08-14). Data as JSON: /api/errors/b6a9b3008503b8f8. Report an issue: GitHub.