How to automatically tag file by name or extension I was wondering if there is a way to automatically tag a file as it reaches your computer, like downloads, copying from an external drive, etc. I would like to simulate gmail filters, like labelling every email as it reaches your mail.

I would prefer if we could do this by name, but if it could be done by extension, that would be ok too.
Apple offer Folder Actions to attach AppleScripts to folders. You can attach an AppleScript to perform any task with incoming files to a specific folder.

See Folder Actions Tutorial: Automation, Meet the Filesystem for a tutorial and step-by-step guide.