SeleniumHQ/selenium · error · WebDriverException

Value of a session permission must be set to True or False.

Error message

Value of a session permission must be set to True or False.

What it means

Safari set_permission toggles a session permission and requires a bool value; any non-bool raises WebDriverException.

Source

Thrown at py/selenium/webdriver/safari/webdriver.py:79

    def quit(self):
        """Closes the browser and shuts down the SafariDriver executable."""
        try:
            super().quit()
        except Exception:
            # We don't care about the message because something probably has gone wrong
            pass
        finally:
            if not self.service.reuse_service:
                self.service.stop()

    # safaridriver extension commands. The canonical command support matrix is here:
    # https://developer.apple.com/library/content/documentation/NetworkingInternetWeb/Conceptual/WebDriverEndpointDoc/Commands/Commands.html

    # First available in Safari 11.1 and Safari Technology Preview 41.
    def set_permission(self, permission, value):
        if not isinstance(value, bool):
            raise WebDriverException("Value of a session permission must be set to True or False.")

        payload = {permission: value}
        self.execute("SET_PERMISSIONS", {"permissions": payload})

    # First available in Safari 11.1 and Safari Technology Preview 41.
    def get_permission(self, permission):
        payload = self.execute("GET_PERMISSIONS")["value"]
        permissions = payload["permissions"]
        if not permissions:
            return None

        if permission not in permissions:
            return None

        value = permissions[permission]
        if not isinstance(value, bool):
            return None

View on GitHub (pinned to aa36b38e69)

Solutions

  1. Pass True/False explicitly.
  2. Coerce carefully - note bool('false') is True, so parse strings explicitly.

Example fix

# before
driver.set_permission("clipboard", "true")

# after
driver.set_permission("clipboard", True)
Defensive patterns

Strategy: validation

Validate before calling

def permission_value(v) -> bool:
    if isinstance(v, bool):
        return v
    if isinstance(v, str) and v.lower() in ("true", "false"):
        return v.lower() == "true"
    raise WebDriverException("permission value must be bool")

Prevention

When it happens

Trigger: driver.set_permission('safari:permission', 1), set_permission(..., 'yes'), or set_permission(..., None).

Common situations: Reading a permission preference from config/env as a string or int.

Related errors

AI-assisted analysis of SeleniumHQ/selenium@aa36b38e69 (2026-08-14). Data as JSON: /api/errors/9e0f83fb72c95890. Report an issue: GitHub.