The benefits and limitations of headless browser testing

What is headless browser testing?

Headless browser testing is essentially web UI testing, but it uses tools that let tests run without loading a complete web browser. These testing tools send requests the same way a standard web browser does and receive the same HTML, CSS and JavaScript files back.

The key difference is that they don't render these files in a GUI. In the headless testing process, the headless browser builds an internal model for the webpage and lets tests interact with objects on the page -- the same way they would with a normal web browser, all without the additional overhead of a GUI.

Why is headless browser testing important?

Headless browser testing is crucial for modern web development and quick validation of web applications. Not rendering the GUI enables faster test execution and lower resource consumption. This efficiency is particularly valuable in CI/CD pipelines, where rapid feedback on code changes is essential. Headless testing also enables parallel execution of multiple tests, significantly reducing the time required for larger test suites.

Headless browser testing is crucial for modern web development and quick validation of web applications.

This is valuable in various use cases, including cross-browser compatibility and regression testing.

The importance of headless browser testing becomes even more apparent when considering the scale of modern web applications. Development teams often need to run thousands of tests across different environments and configurations. By eliminating the need to render visual elements of the browser UI, headless testing can execute these test suites much faster while maintaining the same level of validation for core functionality, API interactions and Document Object Model (DOM) manipulations.

What frameworks use headless browser testing?

Most common testing frameworks have implemented headless browser testing, with each offering unique approaches and capabilities.

Playwright, a test automation tool developed by Microsoft, has gained significant traction due to its modern architecture and built-in support for multiple browser engines, including Chromium, Firefox and WebKit. It provides comprehensive APIs for automation and testing, with particularly strong support for modern web features, like shadow DOM and network interception. Playwright's ability to run tests in parallel across different browser contexts makes it especially powerful for large-scale testing scenarios.

Cypress, a popular open source end-to-end testing framework, takes a slightly different approach by running directly in the browser environment. This gives it direct access to the application under test, enabling more reliable automation and detailed debugging capabilities. While it traditionally focused on Chrome-based testing, recent versions have been updated to support Firefox and Edge in headless modes.

Selenium, one of the oldest and most widely used testing frameworks, continues to support headless testing across various browsers through WebDriver implementations. Its mature ecosystem and broad browser support make it a reliable choice for organizations with established testing practices. However, Selenium tests might require more setup and configuration than newer frameworks, like Playwright or Cypress.

Other browser automation tools that can be useful for headless browser testing include the following:

• Puppeteer, a Node.js library for controlling Headless Chrome.
• Splash, a Python-based headless browser built on Safari's browser engine, WebKit.
• HtmlUnit, a headless browser based on Java.

The above tools are not full end-to-end testing frameworks, such as Playwright, Cypress and Selenium, but they might be valuable in select testing scenarios -- for example, if you need to check a specific UI element quickly.

Advantages of headless browser testing

There are significant benefits of headless browser testing, including the following:

• Faster test runs. The biggest motivation to choose headless browsers over testing with a traditional browser is that headless browsers shorten the time it takes to run a test suite. Headless browsers can run automated UI tests faster because they don't render UI elements in a GUI. The time required to display something in your browser is significant; by eliminating that step, a headless browser can run tests quicker than a traditional web browser.
• Increased hardware efficiency. Because headless browsers don't render UI elements, they run more efficiently than real browsers and can, therefore, increase the efficiency of the hardware you use to run tests. Similarly, running tests with a headless browser can often significantly increase the number of tests you can run in parallel because the load per test on the hardware is lower. More tests running in parallel means less time overall running your test suite.
• Easier-to-run tests in a CI/CD pipeline. Another benefit of running tests with headless browsers is the ease of running tests in a CI/CD pipeline. Often, your pipeline runs on a remote machine, where it isn't always possible to launch a traditional browser. If you're already running headless tests locally, transitioning these to run on a remote machine is often straightforward.

Disadvantages of headless browser testing

There are some limitations with headless browser testing, including the following:

• Unpredictable browser behavior. The tradeoff of skipping the step to render elements in a UI is that headless browsers don't always behave the same way traditional web browsers do. The webpage can behave differently even when comparing one traditional web browser to another. This difference in behavior is due to subtle variations in how browsers render UI elements generated from a webpage's HTML, CSS and JavaScript content. There are high-level standards for how web browsers should render content. Still, there can be minor unexpected differences between browsers, the same way that a Word document saved in Microsoft Word might look different if opened in Google Docs.
• Potentially unsuitable for visual elements. In the past, headless browser testing was not well suited for tests focused on an application's visual elements. But headless browsers have come a long way, and a 2023 update to Google Chrome's headless browser has merged the code paths of Headless and Headful mode, where the only difference between the two modes is that Chrome Headless mode creates but doesn't display any Chrome browser windows. Since Headless mode creates the browser windows but does not display them, it becomes possible to test the visuals of a web application headlessly. Certainly, testers must independently validate the claim that Headless and Headful Chrome are identical except for the UI. Regardless, this update is a huge step forward for headless browser functionality and further contributes to the advantages of using headless browsers for testing.
• Potentially difficult debugging. Most tests that run with a traditional browser provide a screenshot when a test fails. That makes it easy to observe the visual state of the application at the time of the failure. With headless browsers, there's no screenshot capability, so you must read over an error message telling you which selector couldn't be located. Without the bigger picture, it's difficult to understand a test failure. In this case, you can resort to the functionality built into headless browsers that lets you print out a page's HTML source to understand the state of an application.

Editor's note: This article was originally published in 2023 and republished in 2025 with content updates and additions.

Matt Grasberger is a DevOps engineer with experience in test automation, software development, and designing automated processes to reduce work.