What Is a Headless Browser?

what is a headless browser
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A headless browser is a web browser that doesn’t have a user interface. It works just like any other website browser, but it’s not visible to users and runs in the background.

Table of Contents

How Does a Headless Browser Work?

Headless browsers are mostly used for testing. They’re able to run browser tests without rendering the UI or GUI. Headless browser testing is done via a command-line interface or utilising network communication. 


Headless browsers can parse JavaScript, click on links and buttons, test downloads and automatically perform other actions. Basically, they can do every action that can be done on a regular web browser, but everything happens in the backend and much faster.

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Popular Headless Browsers

Regular browsers may also have headless modes, such as headless Firefox and Google Chrome

These are the most popular and widely used headless browsers or tools that work in the headless environment:


  • Google Chrome — a lightweight web browser that saves heaps of memory. The Google Chrome version 59 or higher can run in a headless environment and provides the usual web browser context. The browser can take screenshots, create PDF files, and is a good choice for page navigation testing. 
  • Mozilla Firefox — from version 56 and up, Mozilla Firefox can run in headless mode and perform various tasks. It’s a helpful tool for cross-browser testing because connecting different APIs enables headless browser testing for different use cases. Headless Firefox is often used together with Selenium or Slimmer JS.
  • PhantomJS — a headless WebKit used for complex tasks. PhantomJS is an open-source project that developers are constantly updating. Used together with CasperJS, this is a handy tool for testing website navigations and finding the weak spots. 
  • TriftleJS — a headless Internet Explorer browser. It uses the V8 engine for running testing scripts. TriftleJS is a good option for test automation. PhantomJS users will find this browser easy to use.
  • HTMLUnit — a headless option for Java developers. This tool helps automate different user behaviour scenarios. It can fill out and submit various forms, click on links, and test website redirections, among other tasks. HTMLUnit can also simulate a few different browsers for testing.

Advantages of Headless Browsers

Headless browsers have a few advantages. Here are the main ones:


  • Speed — hands down, this is the main benefit of headless browsers. They can automate and perform tasks much quicker than any other browser, which saves loads of testing time.
  • Memory — multiple browsers can run in parallel in a headless mode and perform tasks simultaneously without using up too much memory. They don’t need to load the browser GUI, which saves a lot of space.
  • Resources — running multiple tests on one machine at the same time is not a problem for headless browsers. They allow performing many tasks with little resources.

Disadvantages of Headless Browsers

While headless browsers have many benefits, they also contain a few limitations that are worth mentioning:


  • No GUI — the main limitation of all headless browsers is the fact that they’re headless. Testing in an environment without the GUI may be beneficial for finding bugs and loopholes, but at the end of the day, users will be visiting your websites with a regular browser. 
  • Additional tests — in most cases, even when testing in a headless mode, developers also need to run tests with a regular browser. Some bugs may not even appear on a headless mode and only impact the users with regular browsers.
  • Speed — previously named as a benefit, speed may also be a limitation for headless browser testing. The browsers are so fast that they can sometimes miss the bugs developers are trying to catch.


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Headless Browsers: Use Cases

Testing is one of the main tasks headless browsers are used for, but it’s not the only one. Here are the main use cases:

• Automating Tests

Headless browsers can automatically run on websites to test their functionalities. For example, they can automatically fill out and submit forms, click on links, etc. developers can run basic unit tests with headless tools. Headless testing saves time and effort.

• Web Scraping

Web scraping is another common use case for headless browsers. Browsers can quickly navigate websites and extract data. Datacenter proxies are essential for web scraping data from websites because they allow gathering data using different IP addresses.

• Automating Web Interactions

Clicking on links, submitting forms, and filling out various information can be automated in a headless environment. Headless browsers can mimic most interactions that regular users perform on a website. 

• Layout Testing

Headless tools can render and interpret CSS and HTML like any regular browsers. This is helpful for testing website layout and style elements, for example, checking the default page width or finding the coordinates of certain elements. Headless tools can also test JavaScript and AJAX execution and automate screen captures.


Headless browsers are browsers without a Graphical User Interface. This makes them a great tool for automating various tasks in a headless testing environment. Developers and software engineers use browsers in headless mode for automated tests, web scraping, layout testing, and other tasks.


Some popular browsers, such as Google Chrome and Mozilla Firefox, have headless versions. Automated headless browser testing can also be done with different tools, such as PhantomJS, HTMLUnit, and others. 


While automation has many benefits, such as speed, saved memory and resources, it also comes with some limitations. In most cases, the headless browser testing also needs to be done with a regular web browser that returns the GUI.


Headless browsers are often used together with proxies because they help perform various tasks quickly and without getting blocked by a website.

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