How do I validate both HTML and CSS?

You can use CSS HTML Validator for Windows, Mac, and Linux to validate both HTML and CSS at the same time.

How can I download an HTML validator?

You can download an HTML validator by downloading CSS HTML Validator for Windows, Mac, or Linux at htmlvalidator.com.

How do you validate HTML?

To validate an HTML document, download and install CSS HTML Validator for Windows and then open the HTML file or URL that you want to validate. Press F6 and the HTML validation results will appear in the Results Window.

How do you validate CSS?

To validate a CSS document, download and install CSS HTML Validator for Windows and then open the CSS file or URL that you want to validate. Press F6 and the CSS validation results will appear in the Results Window.

How do you check for broken links?

To check for broken links, download and install CSS HTML Validator for Windows and then open the document or URL that you want to check. Press Alt+L and the link check results will appear in the Results Window.

How do you check accessibility?

To check accessibility, download and install CSS HTML Validator for Windows and then open the HTML document or URL that you want to check. Choose 'Validate > Accessibility message only' and the results will appear in the Results Window.

How do you check for SEO issues?

To check for search engine SEO issues, download and install CSS HTML Validator for Windows and then open the HTML document or URL that you want to check. Choose 'Validate > Search engine message only' and the results will appear in the Results Window.

Is there an HTML and CSS validator for Linux?

Yes, there is a command line tool for Linux (htmlval) that checks HTML and CSS documents. It is based on the validation engine in CSS HTML Validator for Windows.

Is there an HTML and CSS validator for Mac?

Yes, there is a command line tool for Mac and macOS (htmlval) that checks HTML and CSS documents. It is based on the validation engine in CSS HTML Validator for Windows.

Download CSS HTML Validator

Version 26.02 Version 2026/v26.02 is now available.

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More download locations (Windows) • htmlval for Mac • htmlval for Linux

OPTIONAL: Print this short Quick Start Guide to help you get started.

Downloads for Registered Users with Paid Licenses

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After Downloading (Windows Only)

After downloading a Windows setup installer, run it and answer Yes to the User Account Control prompt then follow the simple installation instructions. The setup program is digitally signed by AI Internet Solutions LLC (do not run it if it is not).

IMPORTANT: On some systems it may take up to 1 to 2 minutes for the User Account Control dialog to appear because the system is checking the file.

If the User Account Control dialog does not appear or you get an error message like "Error 5: Access is denied." then please try one or more of the following:

Run the setup program by right-clicking on it and choosing Run as administrator.
If the program fails to install or run then temporarily disable any security software like anti-virus, anti-malware, and anti-spyware software. These programs may prevent software from installing or running properly. In most cases we recommend using only Windows Security / Microsoft Defender because it causes the least amount of problems with legitimate software.

Htmlval for Mac and Linux (w/FREE Limited Version)

A new Mac (macOS) and Linux command line (console) tool based on the core validation engine in CSS HTML Validator is now available. Visit htmlval for Mac or htmlval for Linux to download a FREE limited version.

Download Dictionaries (Windows Only)

Download Dictionaries

Additional dictionaries are available to support more languages.

A dictionary editing tool is also available. This tool lets you create your own custom dictionaries.

FREE Online HTML & CSS Validator Powered by CSS HTML Validator Pro

Try our online HTML & CSS validator at htmlval.com.