https://www.drupal.org/project/w3c_validator
The W3C Validator module uses W3C standards to tell you if your web pages are properly formed or if there are issues to fix. This HTML and CSS checker helps your SEO because badly-written pages might confuse the Google bot or even your visitors’ browser. Perfection is not necessary, though. Many websites have problems with their HTML and still rank in Google. It’s better to be safe than sorry.
Install and Enable the W3C Validator Module
- Install the W3C Validator module on your server.
- Go to the Extend page: Click Manage > Extend (Coffee: “extend”) or visit http://yourDrupal8site.dev/admin/modules in your browser.
- Select the checkbox next to “W3C Validator” and click the Install button at the bottom of the page. There are no separate permissions required for the W3C Validator module.
Configure the W3C Validator module
- Click Manage > Reports > W3C Validation Report (Coffee: “w3c”) or visit http://yourDrupal8site.dev/admin/reports/w3c_validator in your browser.
- Configure the module as shown above: a. Uncheck “Validate as logged user.” Google visits your website as an anonymous visitor, so that’s what you should validate.
- Click the Re-validate all pages’ button. You will be asked if you’re sure. Click the Confirm button.
- The next page shows you the warning and errors that the validator has returned on each page.
- Click the drop down arrow next to a page to see the specific errors for that page.
You can turn these errors and warnings over to your developer or themer. W3C validator is strict while Googlebot is much more forgiving. In other words, fix the big problems and knock out as many as your budget allows without obsessing over every single error.
