tar.gz is a file extension for tar archive compressed with gzip. It is a common format for distributing files in Linux.

You can view the list of content of the archive without having to uncompress by using the tf option with the tar command in the command line as the following; 

$ tar tf filename.tar.gz

The command will output the list of files contained in the archive. If the list is long, pipe the output to less for easier viewing, as the following; 

$ tar tf filename.tar.gz | less