Console and logs

Capturing the browser’s console output and JavaScript errors with BiDi, and turning up Selenium’s own logging to see what the bindings and the driver are doing.

Something went wrong, and the only evidence is a failed assertion. There are three separate streams of information that could explain it: what the page wrote to the browser console, what exception JavaScript threw, and what Selenium itself was sending to and receiving from the driver. By default you see none of them.

Browser console and JavaScript errors. With WebDriver BiDi enabled, the log module streams console entries and uncaught JavaScript exceptions to your test as they happen. Register a handler before the action you want to observe, then assert on the entries it collects. This is the cross-browser, standards-based replacement for the old Chromium-only log retrieval, and it catches errors the page swallowed before a user would have seen them.

Selenium’s own logging. Each binding logs through its language’s standard logging facility: java.util.logging in Java, the logging module in Python, Selenium’s Log class in .NET, and Selenium::WebDriver.logger in Ruby. Raising the level to debug shows every command sent to the driver and every response, which is usually enough to tell whether the problem is in your code, the driver or the browser. Logs go to the console by default; add a file handler to keep them with the rest of your test artifacts.

Driver logs. The browser driver (chromedriver, geckodriver, and so on) keeps its own log, configured through the driver’s service class. Reach for it when the browser fails to start or crashes mid-session.

Collect console messages with BiDi:

        try (LogInspector logInspector = new LogInspector(driver)) {
            CompletableFuture<ConsoleLogEntry> future = new CompletableFuture<>();
            logInspector.onConsoleEntry(future::complete);

            driver.get("https://www.selenium.dev/selenium/web/bidi/logEntryAdded.html");
            driver.findElement(By.id("consoleLog")).click();

            ConsoleLogEntry logEntry = future.get(5, TimeUnit.SECONDS);

            Assertions.assertEquals("Hello, world!", logEntry.getText());
    driver.script.add_console_message_handler(log_entries.append)

    driver.find_element(By.ID, "consoleLog").click()
    WebDriverWait(driver, 5).until(lambda _: log_entries)
    assert log_entries[0].text == "Hello, world!"
    const inspector = await LogInspector(driver)
    await inspector.onConsoleEntry(function (log) {
      logEntry = log
    })

    await driver.get('https://www.selenium.dev/selenium/web/bidi/logEntryAdded.html')
    await driver.findElement({id: 'consoleLog'}).click()

    assert.equal(logEntry.text, 'Hello, world!')

Collect JavaScript exceptions with BiDi:

            driver.get("https://www.selenium.dev/selenium/web/bidi/logEntryAdded.html");
            driver.findElement(By.id("jsException")).click();

            JavascriptLogEntry logEntry = future.get(5, TimeUnit.SECONDS);

            Assertions.assertEquals("Error: Not working", logEntry.getText());
    driver.script.add_javascript_error_handler(log_entries.append)

    driver.find_element(By.ID, "jsException").click()
    WebDriverWait(driver, 5).until(lambda _: log_entries)
    assert log_entries[0].text == "Error: Not working"
    const inspector = await LogInspector(driver)
    await inspector.onJavascriptException(function (log) {
      logEntry = log
    })

    await driver.get('https://www.selenium.dev/selenium/web/bidi/logEntryAdded.html')
    await driver.findElement({id: 'jsException'}).click()

    assert.equal(logEntry.text, 'Error: Not working')

Turn up Selenium’s own logging:

        Logger logger = Logger.getLogger("");
        logger.setLevel(Level.FINE);
        Arrays.stream(logger.getHandlers()).forEach(handler -> {
            handler.setLevel(Level.FINE);
    logger = logging.getLogger('selenium')

    logger.setLevel(logging.DEBUG)
            Log.SetLevel(LogEventLevel.Trace);
    logger = Selenium::WebDriver.logger

    logger.level = :debug

Common errors

  • JavascriptException: a script you executed through WebDriver threw. The BiDi log module shows the page’s own errors, which this exception does not cover.
  • UnsupportedCommandException: BiDi was not enabled for the session, so the log module is unavailable.

Reference

Last modified November 3, 2026: C2: Task-based Guides section (#2911) (017f4413240)