When you build own website it is a good idea to keep all links and all filenames typed in lowercase to avoid possible case errors. Windows is not a case sensitive system, it treads index.html and Index.html as one file. So, if your web page has case errors in links (say, you wrote href =Index.html while the actual filename is index.html) it will work perfectly on you local computer under the Windows, but this link may become broken when you put this page on your server. This is because most servers use Unix related systems, and these systems are case sensitive.

HTML Link Validator has useful lowercase tools:

This button on Link Validator toolbar allow you to convert the link under cursor to lowercase.

Converts all local links in the current file to lowercase.
Note: The links to remote files (i.e. links like "http://www.MySite.com/Index.htm") will not be converted to eliminate possible case errors.

Allow user to convert any file name (or all file names in a folder) to lowercase.
Note: The links in your HTML files will not be changed.