Crucial to the user experience. Works with any theme.

Well configured on-site search is absolutely crucial to the user experience, and with WP Extended Search you can configure the native WordPress search to your hearts content. If you use WooCommerce, you can include (or exclude) product category, tags etc, and if you add other custom post types or fields, there is no way around fine-tuning search to include those fields. The greatest thing about WP Extended Search is that it tweaks the native search functionality, and it’s thus compatible with whatever theme it’s used in combination with.