How to Fix the 10 Most Common HTML Errors

Every HTML validator report has the same usual suspects. Here are the 10 errors I see most often,with the fix for each one. I built ValidateHTML to catch these automatically, but knowing why they matter is just as important as fixing them. 1. Missing alt Attribute on Images Every <img> needs an alt . Screen readers depend on it. Google Images indexes it. It's the #1 accessibility violation on the web. ❌ Invalid: <img src= "hero.jpg" > ✓ Valid: <img src= "hero.jpg" alt= "Mountain landscape at sunset" > For decorative images, use alt="" . 2. Unclosed Tags A missing </p> or </div> can shift your entire layout. Browsers auto-close silently,usually wrong. ❌ Invalid: <div class= "card" > <p> Some content </div> ✓ Valid: <div class= "card" > <p> Some content </p> </div> 3. Deprecated Elements <center> , <font> , <marquee> ,still render, but signal outdated code. ❌ Deprecated: <center> <font size= "5" color= "red" > Hello </font> </center> ✓ Modern: <div style= "text-align: center" > <span sty