HTML Validator Online is a free browser-based tool that checks HTML markup and reports common issues found in your code. Paste your HTML, import a file, load a sample, or fetch a public URL to review the markup before publishing.
The tool works as an HTML checker using HTMLHint-based rules and returns a JSON report with the issue severity, line, column, rule, and message. This makes it easier to locate and fix problems in your HTML source.
Use validate HTML online when you want to catch common markup problems before deploying a webpage. The tool can also help with HTML validation, CMS content checks, and basic email HTML hygiene.
Note: This is an HTMLHint-based markup validator, not the W3C Nu Html Checker. Use the results as practical browser-based feedback rather than as an official W3C validation result.
Step 1: Add Your HTML
Paste HTML into the editor, import a file, load the sample, or fetch a public URL.
Step 2: Validate Your Code
Run Validate to check the markup and generate a JSON list of detected issues.
Step 3: Review the Results
Check the severity, line, column, rule, and message for each reported issue.
Step 4: Fix and Validate Again
Update your HTML based on the reported issues and run the validation again to check the updated markup.
Pre-Publish HTML Checks
Use the HTML errors checker to find common markup problems before publishing a webpage.
Validate CMS Content
Check HTML copied from rich-text editors or CMS platforms before adding it to your website.
Check Email HTML
Run HTML validation on email templates to identify common structural issues before sending a campaign.
Debug HTML Markup
Use the markup validator to locate reported issues and make corrections directly in your source code.
HTML Validator supports:
After fixes, preview in HTML Viewer or tidy with HTML Formatter.
