Playwright on Windows (WebView2 CDP)

Configure the first WebView

Set remote_debugging_port on the first FletWebviewAll created in the process. WebView2 uses one shared browser environment, so later WebViews inherit the same CDP endpoint. If another WebView is created first, restart the application before enabling the port.

Remote debugging is intended for development and test automation. The CDP endpoint has no application-level authentication and can inspect every WebView in the shared environment. Always leave remote_debugging_port=None in production.

Start the Flet app

import flet as ft
from flet_webview_all import FletWebviewAll


def main(page: ft.Page):
    webview = FletWebviewAll(
        url="https://example.com",
        remote_debugging_port=9222,
        expand=True,
    )
    page.add(webview)


ft.run(main)

The port must be between 1 and 65535. It is a startup-time setting; changing it after the WebView2 environment has initialized requires restarting the app. If you prefer environment-based configuration:

$env:FLET_WEBVIEW_ALL_REMOTE_DEBUGGING_PORT = "9222"
flet run src/main.py

import os

port = os.getenv("FLET_WEBVIEW_ALL_REMOTE_DEBUGGING_PORT")
webview = FletWebviewAll(
    url="https://example.com",
    remote_debugging_port=int(port) if port else None,
)

Verify the endpoint

Before attaching Playwright, open http://127.0.0.1:9222/json/list in a browser or request it with PowerShell:

Invoke-RestMethod http://127.0.0.1:9222/json/list |
    Select-Object id, title, url, webSocketDebuggerUrl

The response should contain a page target for the visible WebView2 document.

Attach with Playwright

Install Playwright in a separate test environment with pip install playwright (the WebView2 browser is already installed by the Flet desktop runtime):

import asyncio
from playwright.async_api import async_playwright


async def attach_and_test():
    async with async_playwright() as playwright:
        browser = await playwright.chromium.connect_over_cdp(
            "http://127.0.0.1:9222"
        )
        pages = [
            page
            for context in browser.contexts
            for page in context.pages
        ]
        if not pages:
            raise RuntimeError("No WebView2 page target was found")

        page = next(
            page for page in pages
            if page.url.startswith("https://example.com")
        )
        print("URL:", page.url)
        print("Title:", await page.title())
        await page.screenshot(path="webview-screenshot.png")


asyncio.run(attach_and_test())

Test a JavaScript bridge with Playwright

When the Flet control registers javascript_channels=["FletBridge"], the page can call FletBridge.postMessage(...). Playwright can exercise the page while Flet receives the resulting on_javascript_message event (see Events):

await page.evaluate("FletBridge.postMessage('message from Playwright')")

Multiple WebViews

Every WebView in the process shares the first environment and CDP endpoint. A second control may omit the port or repeat exactly the same value:

page.add(
    ft.Row([
        FletWebviewAll(url="https://example.com", remote_debugging_port=9222),
        FletWebviewAll(url="https://flet.dev"),  # inherits port 9222
    ], expand=True)
)

Do not use a different port on the second control, and do not create any WebView before the control that configures the port.

See remote_debugging_port for the property itself, and Debugging & DevTools for the non-Windows, non-Playwright debugging options.