Hi, here are my developing WordPress plugins which I use in my daily routine:
To see the queries and loading scripts/styles in my WordPress site, I use:
Query Monitor: https://wordpress.org/plugins/query-monitor/
To show the WP template on which I am currently on, the plugin I use is:
Show Current Template: https://wordpress.org/plugins/show-current-template/
...and this one is pretty much the same:
Which Template: https://wordpress.org/plugins/which-template/
Plugin to see whether everything is fine with our WP theme. It runs a quick scan (the same as doing a spell check before submitting an article):
Theme Check: https://wordpress.org/plugins/theme-check/
Password protect your whole WordPress site with a 1 password (you can use it as Under Construction WP plugin alternative). You can also allow (whitelist) your IP address :-)
Password Protected: https://wordpress.org/plugins/password-protected/