A HyperText Markup Language (HTML) debugger is an editing program that tests HTML markup and locates any faults or errors in the code. Modern HTML debugging tools work as HTML validators and also generally support the common web languages, allowing debugging of JavaScript, Cascading Style Sheets (CSS), Hypertext Preprocessor (PHP), and Extensible Markup Language (XML). HTML debugging programs often offer advanced tools for managing and correcting layout and style mistakes. Along with validating and managing code, HTML debugging programs allow ways for developers to monitor their page performance and network activity.
Developers often turn to an HTML debugger for its ease of use in correcting layout mistakes. The debugging tool effectively provides a graphical user interface for editing the page contents. A typical debugger will display both a preview of the page and the underlying code. Inspecting elements within the page preview provides a clear view of the tag and style attributes affecting the selected element. If the debugger supports live tweaking, then changes made are reflected immediately in the preview window, allowing for quick corrections.
Other tools an HTML debugger may offer include trace style functions and border illustration. Trace style functions allow the developer to figure out which style sheets affect an element and observe the interplay between style sheets. Border illustrations provide graphical lines that mark the edges of normally invisible borders, like the margins around a text field.
Most modern iterations of the HTML debugger include a JavaScript debugger for testing and validating any JavaScript included in the code. Some JavaScript debuggers will only provide basic features such as finding errors in the JavaScript or providing a log of everything that occurs as the code executes, while others offer more advanced features. Some advanced features include the ability to measure the performance of the code and find bottlenecks, and the ability to step through the code, execution by execution.
An HTML debugger allows a developer to test the markup and code written in a variety of browser platforms. Each web browser follows its own internal rules when choosing how to display or process an element of a website. Computing differences mean elements don’t always appear the same in different browsers. Any discrepancies in display or program execution between browsers can then be detected and corrected to ensure all users have the same experience.
Monitoring network activity is another important function of an HTML debugger. The debugger monitors how long files take to download and how long JavaScript commands take to complete. If managing speed and bandwidth are a concern, this information can give a developer a better idea of how a page can be modified to optimize its speed and decrease its overall size.