Deprecated HTML tags checker

What the deprecated HTML tags checker does

This tool scans a webpage for HTML tags that are obsolete or deprecated in modern HTML specifications and reports how many it found. It highlights legacy markup that may cause inconsistent rendering or maintenance headaches.

HTML has evolved considerably. Tags such as <font>, <center>, <marquee>, and <big> were once common but are now obsolete. Browsers often still render them for backward compatibility, which is precisely why they linger in old codebases: the page looks fine, so nobody notices the technical debt.

Why deprecated tags are a problem

Obsolete tags are not guaranteed to behave consistently across browsers and rendering engines. They also mix presentation with structure, making styles harder to maintain. Replacing them with semantic HTML and CSS produces cleaner markup that is easier to style, test, and update.

Deprecated tags can also affect accessibility. Elements like <marquee> create motion that users cannot easily pause, and layout achieved with <center> or table hacks may break on different screen sizes. Modern CSS handles these cases more predictably and with better support for responsive design.

How to interpret the results

The tool reports the number of deprecated tags found and lists them. A result of zero means no obsolete tags were detected in the HTML response. A non-zero result is a signal to review the page source and plan replacements, starting with templates that affect many pages.

Prioritize by impact. Tags in shared headers, footers, or content templates propagate across the whole site, so fixing them once yields broad improvement. Tags in a single legacy landing page are lower priority. When replacing a tag, identify what it was doing: if it was purely presentational, move that styling to CSS; if it conveyed structure, choose a semantic element instead.

Common replacements

• <font> and <center> become CSS properties on appropriate elements.
• <big> and <small> usage should be reviewed; <small> remains valid for side comments, while font sizing belongs in CSS.
• <marquee> and <blink> should be removed or replaced with accessible animation.
• Layout tables should become CSS grid or flexbox layouts.
• <frame> and <frameset> should be replaced with <iframe> or modern embedding patterns.

Practical workflow

Run the check on key templates rather than individual pages. Note which deprecated tags appear in shared components, fix those first, and verify rendering after each change. Keep an eye on content migrated from old systems, since legacy markup often survives import processes.

Limitations

The checker reports tags present in the HTML it receives. It does not assess visual rendering or whether a deprecated tag is harmless in a specific context, and dynamically injected legacy markup may not be detected.