If you have created links to external websites using the ‘Web Link’ feature, then this function will check them for you and report any dead links to you.;Please note that this feature will not work if you have entered the links using the text editor.
The Web Link can be found under Build Content & Web Link:

To check your links, you need to be an instructor on the course or a leader on the organisation. 

From within the module, click on the Control Panel link and look for the Course Tools or Organisation Tools option. From here, click on the Link Checker tool

The links will appear in section 1, along with details of whether it is still available, and whether the link is visible to users:

To make a link invisible to users, check the "Hide" box alongside the corresponding link.;Please note that this does not remove the link; it makes it invisible to users.
When you have finished checking your links, click on the Submit button.