In my day job, I do a great deal of development on WordPress sites. I've come a long way in my understanding of the popular CMS software in the last couple years, but I'm still learning something new all the time.
In that spirit, here's a collection of WordPress plugins that I've found to be life changers. I consider them must-installs when working on new sites:
I remember when I started creating custom post types and using ACF. It expanded my perception of what a WordPress site could be. Before discovering ACF, I had to resort to ugly hacks and just kind of lumping posts together with categories and duct tape.
The base ACF is free, but the Pro version is not only an extremely fair price (A$25 at the time of writing), but includes invaluable field types, like the Repeater, Options pages, and the ability to integrate with the new Blocks feature in WP5.
This one may have been abandoned, but it still works as of this writing. It checks for plugin, theme, and core updates regularly, and emails me about it. WordPress being kept updated is crazy important, so it's great to be able to update as soon as possible. Might need to find a replacement for it, though, if it really has been left for rats.
If you're doing any work with user roles, you need this. View Admin As allows you to switch between various roles and capabilities without having to log out, or keep a private browsing window open with another account loaded up.
Which template wound up being loaded? Why is this taking so long to load? WHERE ARE MY PANTS?? Query Monitor adds a wonderful dropdown on the admin bar that helps you find out the answer to all of these, and more.
Dumps all of a post's meta values at the bottom of it's edit screen. See every little bit of information being stashed along side your posts. Why something like this isn't included as a built-in debug tool is beyond me.
Adds the wonderful
vdd() debug methods (substitutes for
print_r, et al), and a gorgeous, very helpful error message via the Whoops error handler.
Just a word of warning though: this seems to crank the error reporting level, so even basic issues stop everything in their tracks. Normally, this is good -- fix it! But I had at least one time where it caused a silent crash, and I couldn't do ANYTHING in WordPress. Not even disable Debug Toolkit. I had to go in and manually remove the plugin from the command line. MOST of the time, it's perfectly great though. Just stay aware.
An interactive PHP console via the admin bar! Instead of hacking in a test or two and dying somewhere, just pop down the console and test out your PHP/WordPress code assumptions in a safe space.