n automation, a browser can run in two modes:

Headed: You see the browser window.

Headless: Runs without a window.

Headless mode is faster and uses less memory. It’s good for running tests on servers or in CI pipelines where no screen is available.

Headed mode is useful when you’re debugging. You can see what the script is doing. This helps find layout bugs or see errors as they happen.

Most tools let you switch with one line of code. For example, in Selenium with Chrome:

options = webdriver.ChromeOptions()
options.add_argument('--headless')
browser = webdriver.Chrome(options=options)

Use headless for daily runs and headed when something fails.