If there is a need to check for errors in the source codes of the site pages, then it is best to use the site validators of the W3C (The World Wide Web Consortium) organization. It is this organization that develops Internet standards, which must comply with any documents posted on the network.
Instructions
Step 1
You can start by checking the HTML source code of a page on your site against the W3C standards. To do this, go to the validator page (https://validator.w3.org) and in the Address field enter the URL of the page to check. This is enough, but if you wish, you can set additional scan parameters - they will appear if you click the More Options link. Click the Check button to start the verification process. In a few seconds, the validator will submit a report on its analysis of the page code. It will be either a congratulation for a flawlessly valid HTML code, or a message about the number of non-conformities found. For each error, it will indicate where it is located and provide a description of it
Step 2
There is a similar validator for checking for errors in CSS code. His address - https://jigsaw.w3.org/css-validator. The procedure differs from checking the HTML code in that this page also has a Russian-language version. Go to the validator's website, enter the address of the page containing the code to be verified, and, if desired, set additional verification parameters by clicking on the "Additional features" link. Then click the "Check" button. If your CSS descriptions are contained in a separate include file, and are not written directly in the page code, then specify the address of this file. The result of the check will also contain either a list of errors with a description, or congratulations on the excellent quality of the CSS code
Step 3
The set of validators on the W3C website also includes a link checker, which checks for links leading to nowhere, i.e. to pages that no longer exist. His address - https://validator.w3.org/checklink. The verification procedure itself is as simple as the previous two - go to the validator's website, enter the URL of the page being checked, specify additional parameters if necessary, and click the Check button. If there are errors in the links, the validator will list them with the codes and their text descriptions.
