HTML Validator & Linter Tool

Validate your HTML code for errors and compliance with web standards. This linter checks syntax, deprecated elements, and accessibility to ensure clean, correct HTML.

HTML Validator & Linter

Validate HTML syntax and check for common issues

HTML Input

How the HTML Validator and Linter Works

This tool analyzes HTML code for syntax errors and common issues. It checks for unclosed tags, deprecated elements, missing accessibility attributes, and best practice violations. Errors and warnings are reported with line numbers for easy correction.

Validation Process

Paste your HTML code into the input area
Click "Validate HTML" to start analysis
The tool parses tags and tracks opening/closing pairs
Unclosed tags are flagged as errors
Deprecated tags trigger warnings
Missing accessibility attributes are noted
Review errors (must fix) and warnings (should fix)
Correct issues and re-validate until clean

Specific Use Cases

Pre-Deployment Quality Check

A developer validates HTML before deploying to production. Catching errors early prevents rendering issues and broken layouts.

Accessibility Compliance

A team checks for missing alt attributes and lang declarations. Fixing these warnings improves accessibility for users with disabilities.

Learning HTML Best Practices

A student learning web development uses the validator to understand proper HTML structure. Warnings explain what needs improvement.

Legacy Code Modernization

A developer updates old HTML files. The validator identifies deprecated tags like <font> and <center> that need replacement.

Code Review Automation

A team lead uses the validator during code reviews. It catches common mistakes automatically, letting reviewers focus on logic.

What to Know Before Using This Tool

Understanding validation results:

Errors are critical issues that break HTML structure
Warnings are best practice recommendations
Unclosed tags cause rendering problems
Deprecated tags still work but should be avoided
Missing DOCTYPE triggers quirks mode in browsers
Inline styles aren't errors but reduce maintainability

Frequently Asked Questions

What's the difference between errors and warnings?

Errors are structural problems that break HTML (unclosed tags, mismatched tags). Warnings are best practice issues (deprecated tags, missing attributes) that don't break rendering but should be fixed.

Why is missing DOCTYPE a warning?

Without DOCTYPE, browsers use quirks mode, which emulates old browser behavior. This can cause inconsistent rendering. Always include <!DOCTYPE html>.

What tags are considered deprecated?

Deprecated tags include: <acronym>, <applet>, <basefont>, <big>, <center>, <font>, <frame>, <frameset>, <marquee>, <s>, <strike>, <tt>, <u>.

Why warn about inline styles?

Inline styles mix content and presentation, making maintenance harder. External CSS is preferred for separation of concerns and reusability.

What accessibility checks are performed?

The validator checks for missing alt attributes on images and missing lang attribute on the html tag. These are essential for screen reader users.

Does valid HTML guarantee correct rendering?

No, valid HTML is necessary but not sufficient. CSS errors, JavaScript bugs, and browser differences can still cause rendering issues. Validation is the first step in quality assurance.

Other Free Tools

Search tools

HTML Validator & Linter Tool