Extension Developer Tools save time for tedious directory and file creation and eliminated small human mistakes.
Visit developer_tools_extension page at GitHub. In the right corner select button 'Clone or Download' and choose Download Zip option. Unarchive it, locate developer_tools_extension version you need, upload code/extensions/developer_tools/ folder to your_site/extensions/ folder.
It is important to make sure that developer_tools directory and directory for cloned template have complete rules to write files (777). For template extension clone, you need to set temporary /extensions/ directory to 777 and for core template clone set /storefront/view/ directory to 777
Read artcile How to Clone default template with dev tools
