Different Single Post Template per Category
Lets a classic theme use single-cat-{slug}.php for posts in a given category, for example a recipe layout for posts filed under Recipes, falling back to the normal template.
Snippet Library
Developer snippets for WordPress
Snippets for developers: debugging helpers, custom cron schedules, body classes, REST API tweaks and admin tools for checking hooks and queries. Building blocks for people who write code for WordPress every day.
Enable Featured Images for Any Theme
Turns on featured image (post thumbnail) support for themes that do not declare it.
Keep Plugin Deprecation Notices Out of debug.log
Stops PHP deprecation notices coming from plugins and themes from filling debug.log, so the real warnings and errors you are looking for stand out while debugging.
Mark Each Block in the Page Source for Administrators
Wraps every rendered block in HTML comments with its name, such as core/group or a plugin's block, when an administrator views a page with ?wpide_blocks=1, to see which block produced which markup.
Register Extra Menu Locations
Adds new menu locations, such as a footer menu and a legal links menu, that you can assign under Appearance > Menus and print with wp_nav_menu() in a classic theme.
Register Page Templates From a Folder Outside the Theme
Adds every PHP file in wp-content/page-templates/ to the page Template menu of classic themes, so custom layouts survive theme switches and updates.
Registered Image Sizes Under Tools
Adds a Tools > Image Sizes screen listing every image size WordPress creates on upload, with its width, height and crop mode, so you can see what themes and plugins have added.
Show Outgoing HTTP Requests in the Admin Bar
Counts the external HTTP requests WordPress, plugins and themes make while building a page, and lists each URL, status and time in an admin bar menu for administrators.
Show the Current Template in the Admin Bar
Displays the theme template file (and block template, on block themes) used for the current page in the admin bar, for administrators only.
Show the Template Parts Used on a Page
Adds a "Template parts" menu to the front-end admin bar for administrators listing every template part loaded on the page, for both classic themes (get_template_part) and block themes.