WordPress Filter Hooks

When to use

• The user needs to override a WordPress setting, query, or flag exposed as a filter (for example pre_option_*, posts_per_page, or upload_mimes).
• The user wants to let other code override a value in their plugin or theme via apply_filters.
• The user wants to change a value WordPress exposes through a filter, such as the_content, the_title, or excerpt_length.

When NOT to use

• Do not use a filter to perform a side effect such as sending mail or writing a file; use an action (add_action/do_action) instead.
• Do not wrap a value in apply_filters when it is fixed configuration only your code sets and no extensibility is wanted.

Core guidance