Orbisius is a no-nonsense child theme creator plugin that’s super easy to use. Just follow the instructions in the video.
PHP Code sniffer is a code validator. In the tutorial: “Using PHP CodeSniffer With WordPress: Installing and Using the WordPress Rules” Tom McFarlin explains how to install the codesniffer with WordPress-specific sniffs.
Then Tom McFarlin gives a demo on a phpcs on the plugin Hello Dolly:
phpcs --standard=WordPress hello-dolly
I have installed the sniffer following the suggestions in McFarlin’s tutorial on a LAMP server with WordPress. So the tool’s in the box.
The “Theme Handbook” is a very good source for developers.
Here is the sitemapgenerator.
Fine template for a widget: https://pippinsplugins.com/simple-wordpress-widget-template/