HTML vs. XHTML: Key Differences Every Web Developer Should Know
HTML is the forgiving markup language that powers most web pages; XHTML is its stricter XML-based cousin that demands well-formed code and lowercase tags.
Devs often blur the two because browsers quietly “fix” broken HTML, making the difference invisible until a project breaks in a validator or when an XML parser refuses to load.
Key Differences
HTML tolerates unclosed tags and mixed case; XHTML enforces lowercase, self-closing slashes, quoted attributes, and one root element. A single unescaped ampersand can crash an XHTML page.
Which One Should You Choose?
Pick HTML5 for speed and universal support; use XHTML only if you need XML pipelines or strict data exchange. Most modern stacks quietly serve HTML5 as text/html anyway.
Can I convert old HTML to XHTML with find-and-replace?
Yes, but you must also fix nesting errors and add XML namespaces—automated linters like html-tidy make this safer.
Will browsers penalize me for using XHTML today?
No penalty, but if served as text/html it behaves like HTML5, nullifying XHTML’s strict benefits.