How to Fix the 10 Most Common HTML Errors

Source: Dev.to

1. Missing alt attribute on “

Every “ needs an alt attribute. Screen readers depend on it, and Google Images indexes it. It’s the #1 accessibility violation on the web.

Invalid

Valid

[Image: Mountain landscape at sunset]

For decorative images, use alt="".

2. Unclosed tags (or)

A missing closing tag can shift your entire layout. Browsers auto‑close silently, usually incorrectly.

Invalid

  Some content

Valid

  
Some content

3. Deprecated elements (,, “)

These tags still render but signal outdated code.

Deprecated

  Hello

Modern

  Hello

4. Missing “

Without a proper doctype, browsers enter quirks mode, causing the box model, margins, tables, and other layout aspects to behave differently.

Always start with

  
  …

5. Missing lang attribute on “

Screen readers may pick the wrong pronunciation, and browser translation can break. One attribute fixes it.

Invalid

Correct

6. Duplicate id attributes

getElementById() returns the first match only, causing anchor links to break and confusing screen readers.

Duplicate

Site header
Page header

Unique

Site header
Page header

7. Invalid element nesting

cannot contain, and cannot contain. Browsers restructure the DOM silently.

Invalid

  This breaks the paragraph

Correct

  
Paragraph text

  Block content

8. Missing viewport meta tag

Without it, mobile browsers render pages at desktop width, preventing responsive CSS from taking effect. Google’s mobile‑first indexing checks for this.

Always include

9. Empty heading tags

An “ (or any heading) with no text breaks the document outline, wastes SEO value, and confuses screen readers.

Empty

## 

With content

## Our Features

10. Inline styles instead of CSS classes

Inline styles are a code smell: they can’t be cached, reused, or maintained efficiently.

Avoid

Text

Better

Text

.error-message {
  color: red;
  font-size: 18px;
  margin: 20px 0;
}

Additional resources

You can paste your HTML or enter any URL in ValidateHTML; it catches all 10 of these errors automatically, shows line numbers, and gives you a quality score (0‑100 with letter grades). Free, no login required.

For detailed guides on each error with step‑by‑step fixes, see the HTML Errors Guide.