Headless browsers support modern web features, including ES6, CSS, and HTML, for end-to-end testing, smoke testing, and UI testing.
To fully leverage a headless browser, it must be combined with developer tools and browser automation libraries, such as Puppeteer. These tools allow you to programmatically control the browser, simulate user interactions, and inspect application behavior in a test environment.
This article explains how headless browsers are utilized in modern web testing and how they differ from traditional browsers.
What is a headless browser?
A headless browser is a web browser without a graphical user interface (GUI). In other words, it has no visible window, tabs, or buttons; the GUI is hidden, making it ideal for dynamic web pages.
A headless browser can load webpages, render HTML/CSS, execute JavaScript, and manage the DOM just like a normal browser would. Modern web browsers, such as Google Chrome (Headless Chrome) and Mozilla Firefox (Headless Firefox), include a built-in headless mode.
Typically, when you launch Chrome, you interact with a graphical user interface (GUI) that includes menus, interactive elements, and the ability to type directly into pages.
However, a headless browser runs without this interface. You can start it from the terminal using specific commands (e.g., with a headless flag), but on its own, it’s not particularly useful.
Source: Chrome for developers 1
Popular headless browsers and frameworks
Selenium WebDriver (Headless Mode)
Selenium WebDriver delegates control to the underlying browser driver (such as ChromeDriver or GeckoDriver), which provides features like headless execution. It communicates with these drivers using the standardized W3C WebDriver Protocol, an official API for browser automation.
Since headless mode only disables the browser’s graphical interface, it does not impact WebDriver’s functionality. All interactions, such as finding elements, sending input, and executing scripts, occur exactly as they would in a regular (headed) browser session.
Playwright
Playwright runs tests in parallel and headless mode by default. No browser window is displayed. Test output is displayed in the terminal or saved in reports. Generating screenshots and performance monitoring are also supported during testing scenarios. You can also switch to headed mode for live observation. The playwright maintains two Chromium builds:
- Lightweight headless shell for performance
- Full Chromium GUI build for headed interaction.
Puppeteer
Puppeteer is a headless browser automation library for Node.js. By default, it operates in headless mode. It is often used to automate Chromium, but for broader browser coverage, other tools like Playwright might be required.
Headless Chrome/Chromium
Chrome introduced a new headless mode in version 112, designed to run the full Chrome browser without displaying a UI.2 This approach improves browser testing for complex websites by maintaining the functionality of a real browser.
Unlike the old headless mode, the new mode preserves all standard browser features, including support for JavaScript execution, DevTools, and browser extensions.
The new headless mode is built on the same codebase as regular Chrome, offering improved compatibility across various testing environments. It is now the default headless mode as of Chrome 132.
What are headless browsers used for?
Headless browsers have become invaluable for various use cases across development, testing, and data processing, including:
1. Automated testing and QA
Headless browsers are commonly used for automation tests to simulate user interactions (clicking links, form submission, navigating pages) without a visible UI.
Instead of interacting via the user interface, automation tasks can be handled entirely through scripts. Many developers prefer using headless mode for automated tests because it reduces overhead while preserving test accuracy.
Graphical browsers need to load images, icons, and interface elements, which adds time and increases testing costs for businesses. In contrast, headless browsers skip loading the GUI, including tabs, bookmarks, and icons.
As a result, running tests on a server without a GUI is significantly faster than using standard browsers. Switching to a headless testing environment can help reduce both testing time and costs.
Web scraping
When the target website for your scraping project contains JavaScript-rendered content that requires interaction, such as clicking buttons, scrolling, or handling authentication and sessions, a headless web browser is recommended. By skipping visual rendering, headless scripts can efficiently collect large volumes of data at high speed.
Many modern websites require session management or user authentication, such as logging in with credentials. For example, LinkedIn is a JavaScript-heavy website that requires users to log in before accessing detailed profile information.
If you try to send a request using only requests or BeautifulSoup, you’ll likely receive a login page instead of the profile data. LinkedIn uses anti-bot measures that detect unauthenticated activity.
You can use these tools in headless mode to automate the login process, preserve the session by storing cookies, and navigate dynamically through the website.
Screenshot and PDF generation
Headless browsers use a “print to PDF” feature to generate a faithful representation of the view. For instance, when you need to archive a visual representation of a web page, a headless browser can capture full-page screenshots and create paginated PDFs. This is more useful than saving the raw HTML.
Server-side rendering for SEO
Server-side rendering is the process of rendering a website’s content on the server before it’s sent to the user. Popular web browsers, such as Google and Bing, rely on web crawlers to scan websites and index their content.
If your site is heavily reliant on JavaScript, crawlers may not be able to view the actual content. A headless browser renders the target page as a user’s browser would. Once all content is rendered, it creates a static HTML version of the page. However, there’s no guarantee it will render everything correctly.
What is headless browser testing?
Headless browser testing refers to running automated tests against a web application using a headless browser. Headless browser testing is heavily used in CI/CD pipelines. In this approach, the testing process focuses on the functional components of a web application while bypassing the graphical rendering of the UI elements. This means that the visual aspects of a webpage, like layout and design, are not rendered or visually checked during headless testing.
Regular UI-based browsers might be resource-intensive when executing parallel tests. The reduced resource usage of headless browsers makes them well-suited for handling numerous tests that run in parallel.
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