new command line tool: unique name
Don't bother. pick any name you want that doesn't collide with something in your current PATH and that no one in your current group recognizes. If the tool becomes popular, you will have a name collision very quickly and can change the name at that time. If your tool is popular enough, you will keep the name. (This happened to git, for example, and the unpopular package previously known as git is still unpopular, while the version control system kept the name.)
Perhaps "don't bother" is a bit strong. Perform some search, exert some effort, but not more than a few hours at most. If you can't find a name collision after a few hours of effort, then the other tool that is using the name is not sufficiently well known to worry about any potential problems.