Custom post type

You create one with register_post_type( 'event', $args ) on the init hook. The name is stored in the post_type column of wp_posts and must be 20 characters or fewer, lowercase. Key arguments are public, has_archive, supports, rewrite, and show_in_rest, which must be true for the block editor and the REST route /wp-json/wp/v2/event.

To count what exists, run wp post list --post_type=event --format=count, or SELECT post_type, COUNT(*) FROM wp_posts GROUP BY post_type to see everything on the site.

A conference site registers a post type called session with has_archive set to program. After deploying, /program/ and /session/keynote-day-1/ both return 404, even though editing sessions in wp-admin works. The code ran, but the rewrite rules were saved before the type existed.

Visiting Settings > Permalinks and clicking Save flushes the rules, and both URLs load. The developer then adds flush_rewrite_rules() to the plugin activation hook only, not to init.

A custom post type defines what kind of thing a post is, while a taxonomy defines how those things are grouped. Events are a type, and Venue or Track is a taxonomy that can attach to events. You can have a type without any taxonomy, and a taxonomy can span multiple types.

Forgetting to flush rewrite rules after registering. Putting register_post_type in the theme, so the content vanishes from wp-admin on a theme switch. Leaving show_in_rest off and wondering why the block editor will not load. Using a name that collides with a reserved word like post, page, or action. Calling flush_rewrite_rules() on every page load.

Put type registration in a plugin, not the theme. Give each type its own capability_type if non-admins will edit them, and write a short note listing the fields it supports. Before launch, hit one single URL and the archive on staging.