WordPress.org

Ready to get started?Download WordPress

Codex

Attention Interested in functions, hooks, classes, or methods? Check out the new WordPress Code Reference!

Plugin API/Filter Reference

This article is a (mostly complete) list of the filter hooks available for use in plugin development in Version 2.1 and above of WordPress. For more information:

Note: If you want to add to or clarify this documentation, please follow the style of the existing entries. Describe what data the filter is applied to, and if the filter function takes additional arguments, describe the argument list.

Post, Page, and Attachment (Upload) Filters

See also #Category Filters, #Author and User Filters, #Link Filters, #Date and Time Filters, and #Administrative Filters below.

Database Reads

Filters in this section are applied to information read from the database, prior to displaying on a page or editing screen.

attachment_fields_to_edit 
applied to the form fields to be displayed when editing an attachment. Called in the get_attachment_fields_to_edit function. Filter function arguments: an array of form fields, the post object.
attachment_icon 
applied to the icon for an attachment in the get_attachment_icon function. Filter function arguments: icon file as an HTML IMG tag, attachment ID.
attachment_innerHTML 
applied to the title to be used for an attachment if there is no icon, in the get_attachment_innerHTML function. Filter function arguments: inner HTML (defaults to the title), attachment ID.
body_class 
applied to the classes for the HTML <body> element. Called in the get_body_class function. Filter function arguments: an array of class names and an array of additional class names that were added to the first array.
content_edit_pre 
applied to post content prior to display for editing.
excerpt_edit_pre 
applied to post excerpt prior to display for editing.
get_attached_file 
applied to the attached file information retrieved by the get_attached_file function. Filter function arguments: file information, attachment ID.
get_enclosed 
applied to the enclosures list for a post by the get_enclosed function.
get_pages 
applied to the list of pages returned by the get_pages function. Filter function arguments: list of pages (each item of which contains a page data array), get_pages function argument list (telling which pages were requested).
get_pung 
applied to the list of pinged URLs for a post by the get_pung function.
get_the_excerpt 
applied to the post's excerpt in the get_the_excerpt function.
get_the_guid 
applied to the post's GUID in the get_the_guid function.
get_to_ping 
applied to the list of URLs to ping for a post by the get_to_ping function.
icon_dir 
applied to the template's image directory in several functions. Basically allows a plugin to specify that icons for MIME types should come from a different location.
icon_dir_uri 
applied to the template's image directory URI in several functions. Basically allows a plugin to specify that icons for MIME types should come from a different location.
post_class 
applied to the classes of the outermost HTML element for a post. Called in the get_post_class function. Filter function arguments: an array of class names, an array of additional class names that were added to the first array, and the post ID.
prepend_attachment 
applied to the HTML to be prepended by the prepend_attachment function.
sanitize_title 
applied to a post title by the sanitize_title function, after stripping out HTML tags.
single_post_title 
applied to the post title when used to create a blog page title by the wp_title and single_post_title functions.
the_content 
applied to the post content retrieved from the database, prior to printing on the screen (also used in some other operations, such as trackbacks).
the_content_rss 
applied to the post content prior to including in an RSS feed. This filter hasn't been functional since 2.7.
the_content_feed 
applied to the post content prior to including in an RSS feed.
the_editor_content 
applied to post content before putting it into a rich editor window.
the_excerpt 
applied to the post excerpt (or post content, if there is no excerpt) retrieved from the database, prior to printing on the screen (also used in some other operations, such as trackbacks).
the_excerpt_rss 
applied to the post excerpt prior to including in an RSS feed.
the_password_form 
applied to the password form for protected posts.
the_tags 
applied to the tags retrieved from the database, prior to printing on the screen.
the_title 
applied to the post title retrieved from the database, prior to printing on the screen (also used in some other operations, such as trackbacks).
the_title_rss 
applied to the post title before including in an RSS feed (after first filtering with the_title.
title_edit_pre 
applied to post title prior to display for editing.
wp_dropdown_pages 
applied to the HTML dropdown list of WordPress pages generated by the wp_dropdown_pages function.
wp_list_pages 
applied to the HTML list generated by the wp_list_pages function.
wp_list_pages_excludes 
applied to the list of excluded pages (an array of page IDs) in the wp_list_pages function.
wp_get_attachment_metadata 
applied to the attachment metadata retrieved by the wp_get_attachment_metadata function. Filter function arguments: meta data, attachment ID.
wp_get_attachment_thumb_file 
applied to the attachment thumbnail file retrieved by the wp_get_attachment_thumb_file function. Filter function arguments: thumbnail file, attachment ID.
wp_get_attachment_thumb_url 
applied to the attachment thumbnail URL retrieved by the wp_get_attachment_thumb_URL function. Filter function arguments: thumbnail URL, attachment ID.
wp_get_attachment_url 
applied to the attachment URL retrieved by the wp_get_attachment_url function. Filter function arguments: URL, attachment ID.
wp_mime_type_icon 
applied to the MIME type icon for an attachment calculated by the wp_mime_type_icon function. Filter function arguments: icon URI calculated, MIME type, post ID.
wp_title 
applied to the blog page title before sending to the browser in the wp_title function.

Database Writes

Filters in this section are applied to information prior to saving to the database.

add_ping 
applied to the new value of the pinged field on a post when a ping is added, prior to saving the new information in the database.
attachment_fields_to_save 
applied to fields associated with an attachment prior to saving them in the database. Called in the media_upload_form_handler function. Filter function arguments: an array of post attributes, an array of attachment fields including the changes submitted from the form.
attachment_max_dims 
applied to the maximum image dimensions before reducing an image size. Filter function input (and return value) is either false (if no maximum dimensions have been specified) or a two-item list (width, height).
category_save_pre 
applied to post category comma-separated list prior to saving it in the database (also used for attachments).
comment_status_pre 
applied to post comment status prior to saving it in the database (also used for attachments).
content_filtered_save_pre 
applied to filtered post content prior to saving it in the database (also used for attachments).
content_save_pre 
applied to post content prior to saving it in the database (also used for attachments).
excerpt_save_pre 
applied to post excerpt prior to saving it in the database (also used for attachments).
name_save_pre 
applied to post name prior to saving it in the database (also used for attachments).
phone_content 
applied to the content of a post submitted by email, before saving.
ping_status_pre 
applied to post ping status prior to saving it in the database (also used for attachments).
post_mime_type_pre 
applied to the MIME type for an attachment prior to saving it in the database.
status_save_pre 
applied to post status prior to saving it in the database.
thumbnail_filename 
applied to the file name for the thumbnail when uploading an image.
wp_thumbnail_creation_size_limit 
applied to the size of the thumbnail when uploading an image. Filter function arguments: max file size, attachment ID, attachment file name.
wp_thumbnail_max_side_length 
applied to the size of the thumbnail when uploading an image. Filter function arguments: image side max size, attachment ID, attachment file name.
title_save_pre 
applied to post title prior to saving it in the database (also used for attachments).
update_attached_file 
applied to the attachment information prior to saving in post metadata in the update_attached_file function. Filter function arguments: attachment information, attachment ID.
wp_delete_file 
applied to an attachment file name just before deleting.
wp_generate_attachment_metadata 
applied to the attachment metadata array before saving in the database.
wp_update_attachment_metadata 
applied to the attachment metadata just before saving in the wp_update_attachment_metadata function. Filter function arguments: meta data, attachment ID.

Comment, Trackback, and Ping Filters

See also #Author and User Filters, #Link Filters, #Date and Time Filters, and #Administrative Filters below.

Database Reads

Filters in this section are applied to information read from the database, prior to displaying on a page or editing screen.

comment_excerpt 
applied to the comment excerpt by the comment_excerpt function. See also get_comment_excerpt.
comment_flood_filter 
applied when someone appears to be flooding your blog with comments. Filter function arguments: already blocked (true/false, whether a previous filtering plugin has already blocked it; set to true and return true to block this comment in a plugin), time of previous comment, time of current comment.
comment_post_redirect 
applied to the redirect location after someone adds a comment. Filter function arguments: redirect location, comment info array.
comment_text 
applied to the comment text before displaying on the screen by the comment_text function, and in the admin menus.
comment_text_rss 
applied to the comment text prior to including in an RSS feed.
comments_array 
applied to the array of comments for a post in the comments_template function. Filter function arguments: array of comment information structures, post ID.
comments_number 
applied to the formatted text giving the number of comments generated by the comments_number function. See also get_comments_number.
get_comment_excerpt 
applied to the comment excerpt read from the database by the get_comment_excerpt function (which is also called by comment_excerpt. See also comment_excerpt.
get_comment_ID 
applied to the comment ID read from the global $comments variable by the get_comment_ID function.
get_comment_text 
applied to the comment text of the current comment in the get_comment_text function, which is also called by the comment_text function.
get_comment_type 
applied to the comment type ("comment", "trackback", or "pingback") by the get_comment_type function (which is also called by comment_type).
get_comments_number 
applied to the comment count read from the $post global variable by the get_comments_number function (which is also called by the comments_number function; see also comments_number filter).
post_comments_feed_link 
applied to the feed URL generated for the comments feed by the comments_rss function.

Database Writes

Filters in this section are applied to information prior to saving to the database.

comment_save_pre 
applied to the comment data just prior to updating/editing comment data. Function arguments: comment data array, with indices "comment_post_ID", "comment_author", "comment_author_email", "comment_author_url", "comment_content", "comment_type", and "user_ID".
pre_comment_approved 
applied to the current comment's approval status (true/false) to allow a plugin to override. Return true/false and set first argument to true/false to approve/disapprove the comment, and use global variables such as $comment_ID to access information about this comment.
pre_comment_content 
applied to the content of a comment prior to saving the comment in the database.
preprocess_comment 
applied to the comment data prior to any other processing, when saving a new comment in the database. Function arguments: comment data array, with indices "comment_post_ID", "comment_author", "comment_author_email", "comment_author_url", "comment_content", "comment_type", and "user_ID".
wp_insert_post_data 
applied to modified and unmodified post data in wp_insert_post() prior to update or insertion of post into database. Function arguments: modified and extended post array and sanitized post array.

Category and Term Filters

See also #Administrative Filters below.

Database Reads

Filters in this section are applied to information read from the database, prior to displaying on a page or editing screen.

category_description 
applied to the "description" field categories by the category_description and [[Template_Tags/wp_list_categories functions. Filter function arguments: description, category ID when called from category_description; description, category information array (all fields from the category table for that particular category) when called from wp_list_categories.
category_feed_link 
applied to the feed URL generated for the category feed by the get_category_feed_link function.
category_link 
applied to the URL created for a category by the get_category_link function. Filter function arguments: link URL, category ID.
get_ancestors 
applied to the list of ancestor IDs returned by the get_ancestors function (which is in turn used by many other functions). Filter function arguments: ancestor IDs array, given object ID, given object type.
get_categories 
applied to the category list generated by the get_categories function (which is in turn used by many other functions). Filter function arguments: category list, get_categories options list.
get_category 
applied to the category information that the get_category function looks up, which is basically an array of all the fields in WordPress's category table for a particular category ID.
list_cats 
called for two different purposes:
  1. the wp_dropdown_categories function uses it to filter the show_option_all and show_option_none arguments (which are used to put options "All" and "None" in category drop-down lists). No additional filter function arguments.
  2. the wp_list_categories function applies it to the category names. Filter function arguments: category name, category information list (all fields from the category table for that particular category).
list_cats_exclusions 
applied to the SQL WHERE statement giving the categories to be excluded by the get_categories function. Typically, a plugin would add to this list, in order to exclude certain categories or groups of categories from category lists. Filter function arguments: excluded category WHERE clause, get_categories options list.
single_cat_title 
applied to the category name when used to create a blog page title by the wp_title and single_cat_title functions.
the_category 
applied to the list of categories (an HTML list with links) created by the get_the_category_list function. Filter function arguments: generated HTML text, list separator being used (empty string means it is a default LI list), parents argument to get_the_category_list.
the_category_rss 
applied to the category list (a list of category XML elements) for a post by the get_the_category_rss function, before including in an RSS feed. Filter function arguments are the list text and the type ("rdf" or "rss" generally).
wp_dropdown_cats 
applied to the drop-down category list (a text string containing HTML option elements) generated by the wp_dropdown_categories function.
wp_list_categories 
applied to the category list (an HTML list) generated by the wp_list_categories function.
wp_get_object_terms 
applied to the list of terms (an array of objects) generated by the wp_get_object_terms function, which is called by a number of category/term related functions, such as get_the_terms and get_the_category.

Database Writes

Filters in this section are applied to information prior to saving to the database.

pre_category_description 
applied to the category desription prior to saving in the database.
pre_category_name 
applied to the category name prior to saving in the database.
pre_category_nicename 
applied to the category nice name prior to saving in the database.

Link Filters

Note: This section contains filters related to links to posts, pages, archives, feeds, etc. For blogroll links, see the #Blogroll Filters section below.

attachment_link 
applied to the calculated attachment permalink by the get_attachment_link function. Filter function arguments: link URL, attachment ID.
author_feed_link 
applied to the feed URL generated for the author feed by the get_author_rss_link function.
author_link 
applied to the author's archive permalink created by the get_author_posts_url function. Filter function arguments: link URL, author ID, author's "nice" name. Note that get_author_posts_url is called within functions wp_list_authors and the_author_posts_link.
comment_reply_link 
applied to the link generated for replying to a specific comment by the get_comment_reply_link function which is called within function comments_template. Filter function arguments: link (string), custom options (array), current comment (object), current post (object).
day_link 
applied to the link URL for a daily archive by the get_day_link function. Filter function arguments: URL, year, month number, day number.
feed_link 
applied to the link URL for a feed by the get_feed_link function. Filter function arguments: URL, type of feed (e.g. "rss2", "atom", etc.).
get_comment_author_link 
applied to the HTML generated for the author's link on a comment, in the get_comment_author_link function (which is also called by comment_author_link. Action function arguments: user name
get_comment_author_url_link 
applied to the HTML generated for the author's lnik on a comment, in the get_comment_author_url_link function (which is also called by comment_author_link).
month_link 
applied to the link URL for a monthly archive by the get_month_link function. Filter function arguments: URL, year, month number.
page_link 
applied to the calculated page URL by the get_page_link function. Filter function arguments: URL, page ID. Note that there is also an internal filter called _get_page_link that can be used to filter the URLS of pages that are not designated as the blog's home page (same arguments).
post_link 
applied to the calculated post permalink by the get_permalink function, which is also called by the the_permalink, post_permalink, previous_post_link, and next_post_link functions. Filter function arguments: permalink URL, post data list.
post_type_link 
applied to the calculated custom post type permalink by the get_post_permalink function.
the_permalink 
applied to the permalink URL for a post prior to printing by function the_permalink.
year_link 
applied to the link URL for a yearly archive by the get_year_link function. Filter function arguments: URL, year.
tag_link 
applied to the URL created for a tag by the get_tag_link function. Filter function arguments: link URL, tag ID.

Date and Time Filters

See also #Link Filters above.

get_comment_date 
applied to the formatted comment date generated by the get_comment_date function (which is also called by comment_date).
get_comment_time 
applied to the formatted comment time in the get_comment_time function (which is also called by comment_time).
get_the_modified_date 
applied to the formatted post modification date generated by the get_the_modified_date function (which is also called by the the_modified_date function).
get_the_modified_time 
applied to the formatted post modification time generated by the get_the_modified_time and get_post_modified_time functions (which are also called by the the_modified_time function).
get_the_time 
applied to the formatted post time generated by the get_the_time and get_post_time functions (which are also called by the the_time function).
the_date 
applied to the formatted post date generated by the the_date function.
the_modified_date 
applied to the formatted post modification date generated by the the_modified_date function.
the_modified_time 
applied to the formatted post modification time generated by the the_modified_time function.
the_time 
applied to the formatted post time generated by the the_time function.
the_weekday 
applied to the post date weekday name generated by the the_weekday function.
the_weekday_date 
applied to the post date weekday name generated by the the_weekday_date function. Function arguments are the weekday name, before text, and after text (before text and after text are added to the weekday name if the current post's weekday is different from the previous post's weekday).

Author and User Filters

See also #Link Filters and #Administrative Filters sections.

login_redirect 
applied to the redirect_to post/get variable during the user login process.

Database Reads

Filters in this section are applied to information read from the database, prior to displaying on a page or editing screen.

author_email 
applied to the comment author's email address retrieved from the database by the comment_author_email function. See also get_comment_author_email.
comment_author 
applied to the comment author's name retrieved from the database by the comment_author function. See also get_comment_author.
comment_author_rss 
applied to the comment author's name prior to including in an RSS feed.
comment_email 
applied to the comment author's email address retrieved from the database by the comment_author_email_link function.
comment_url 
applied to the comment author's URL retrieved from the database by the comment_author_url function (see also get_comment_author_url).
get_comment_author 
applied to the comment author's name retrieved from the database by get_comment_author, which is also called by comment_author. See also comment_author.
get_comment_author_email 
applied to the comment author's email address retrieved from the database by get_comment_author_email, which is also called by comment_author_email. See also author_email.
get_comment_author_IP 
applied to the comment author's IP address retrieved from the database by the get_comment_author_IP function, which is also called by comment_author_IP.
get_comment_author_url 
applied to the comment author's URL retrieved from the database by the get_comment_author_url function, which is also called by comment_author_url. See also comment_url.
login_errors 
applied to the login error message printed on the login screen.
login_headertitle 
applied to the title for the login header URL (Powered by WordPress by default) printed on the login screen.
login_headerurl 
applied to the login header URL (points to wordpress.org by default) printed on the login screen.
login_message 
applied to the login message printed on the login screen.
role_has_cap 
applied to a role's capabilities list in the WP_Role->has_cap function. Filter function arguments are the capabilities list to be filtered, the capability being questioned, and the role's name.
sanitize_user 
applied to a user name by the sanitize_user function. Filter function arguments: user name (after some cleaning up), raw user name, strict (true or false to use strict ASCII or not).
the_author 
applied to a post author's displayed name by the get_the_author function, which is also called by the the_author function.
the_author_email 
applied to a post author's email address by the the_author_email function.

Database Writes

Filters in this section are applied to information prior to saving to the database.

pre_comment_author_email 
applied to a comment author's email address prior to saving the comment in the database.
pre_comment_author_name 
applied to a comment author's user name prior to saving the comment in the database.
pre_comment_author_url 
applied to a comment author's URL prior to saving the comment in the database.
pre_comment_user_agent 
applied to the comment author's user agent prior to saving the comment in the database.
pre_comment_user_ip 
applied to the comment author's IP address prior to saving the comment in the database.
pre_user_id 
applied to the comment author's user ID prior to saving the comment in the database.
pre_user_description 
applied to the user's description prior to saving in the database.
pre_user_display_name 
applied to the user's displayed name prior to saving in the database.
pre_user_email 
applied to the user's email address prior to saving in the database.
pre_user_first_name 
applied to the user's first name prior to saving in the database.
pre_user_last_name 
applied to the user's last name prior to saving in the database.
pre_user_login 
applied to the user's login name prior to saving in the database.
pre_user_nicename 
applied to the user's "nice name" prior to saving in the database.
pre_user_nickname 
applied to the user's nickname prior to saving in the database.
pre_user_url 
applied to the user's URL prior to saving in the database.
registration_errors 
applied to the list of registration errors generated while registering a user for a new account.
user_registration_email 
applied to the user's email address read from the registration page, prior to trying to register the person as a new user.
validate_username 
applied to the validation result on a new user name. Filter function arguments: valid (true/false), user name being validated.

Blogroll Filters

Note: This section contains filters related to blogroll links. For filters related to links to posts, pages, categories, etc., see section #Link Filters above.

get_bookmarks 
applied to link/blogroll database query results by the get_bookmarks function. Filter function arguments: database query results list, get_bookmarks arguments list.
link_category 
applied to the link category by the get_links_list and wp_list_bookmarks functions (as of WordPress 2.2).
link_description 
applied to the link description by the get_links and wp_list_bookmarks functions (as of WordPress 2.2).
link_rating 
applied to the link rating number by the get_linkrating function.
link_title 
applied to the link title by the get_links and wp_list_bookmarks functions (as of WordPress 2.2)
pre_link_description 
applied to the link description prior to saving in the database.
pre_link_image 
applied to the link image prior to saving in the database.
pre_link_name 
applied to the link name prior to saving in the database.
pre_link_notes 
applied to the link notes prior to saving in the database.
pre_link_rel 
applied to the link relation information prior to saving in the database.
pre_link_rss 
applied to the link RSS URL prior to saving in the database.
pre_link_target 
applied to the link target information prior to saving in the database.
pre_link_url 
applied to the link URL prior to saving in the database.

Blog Information and Option Filters

all_options 
applied to the option list retrieved from the database by the get_alloptions function.
bloginfo 
applied to the blog option information retrieved from the database by the bloginfo function, after first retrieving the information with the get_bloginfo function. A second argument $show gives the name of the bloginfo option that was requested. Note that bloginfo("url"), bloginfo("directory") and bloginfo("home") do not use this filtering function (see bloginfo_url).
bloginfo_rss 
applied to the blog option information by function get_bloginfo_rss (which is also called from bloginfo_rss), after first retrieving the information with the get_bloginfo function, stripping out HTML tags, and converting characters appropriately. A second argument $show gives the name of the bloginfo option that was requested.
bloginfo_url 
applied to the the output of bloginfo("url"), bloginfo("directory") and bloginfo("home") before returning the information.
loginout 
applied to the HTML link for logging in and out (generally placed in the sidebar) generated by the wp_loginout function.
option_(option name) 
applied to the option value retrieved from the database by the get_option function, after unserializing (which decodes array-based options). To use this filter, you will need to add filters for specific options names, such as "option_foo" to filter the output of get_option("foo").
pre_option_(option name) 
applied to the option value retrieved from the database by the get_alloptions function, after unserializing (which decodes array-based options). To use this filter, you will need to add filters for specific options names, such as "pre_option_foo" to filter the option "foo".
pre_update_option_(option name) 
applied the option value before being saving to the database to allow overriding the value to be stored. To use this filter, you will need to add filters for specific options names, such as "pre_update_option_foo" to filter the option "foo".
register 
applied to the sidebar link created for the user to register (if allowed) or visit the admin panels (if already logged in) by the wp_register function.
upload_dir 
applied to the directory to be used for uploads calculated by the wp_upload_dir function. Filter function argument is an array with components "dir" (the upload directory path), "url" (the URL of the upload directory), and "error" (which you can set to true if you want to generate an error).
upload_mimes 
allows a filter function to return a list of MIME types for uploads, if there is no MIME list input to the wp_check_filetype function. Filter function argument is an associated list of MIME types whose component names are file extensions (separated by vertical bars) and values are the corresponding MIME types.

General Text Filters

attribute_escape 
applied to post text and other content by the attribute_escape function, which is called in many places in WordPress to change certain characters into HTML attributes before sending to the browser.
js_escape 
applied to JavaScript code before sending to the browser in the js_escape function.

Administrative Filters

The filters in this section are related to the administration screens of WordPress, including content editing screens.

admin_user_info_links 
applied to the user profile and info links in the WordPress admin quick menu.
autosave_interval 
applied to the interval for auto-saving posts.
bulk_actions 
applied to an array of bulk items in admin bulk action dropdowns.
cat_rows 
applied to the category rows HTML generated for managing categories in the admin menus.
comment_edit_pre 
applied to comment content prior to display in the editing screen.
comment_edit_redirect 
applied to the redirect location after someone edits a comment in the admin menus. Filter function arguments: redirect location, comment ID.
comment_moderation_subject 
applied to the mail subject before sending email notifying the administrator of the need to moderate a new comment. Filter function arguments: mail subject, comment ID. Note that this happens inside the default wp_notify_moderator function, which is a "pluggable" function, meaning that plugins can override it; see Plugin API).
comment_moderation_text 
applied to the body of the mail message before sending email notifying the administrator of the need to moderate a new comment. Filter function arguments: mail body text, comment ID. Note that this happens inside the default wp_notify_moderator function, which is a "pluggable" function, meaning that plugins can override it; see Plugin API).
comment_notification_headers 
applied to the mail headers before sending email notifying the post author of a new comment. Filter function arguments: mail header text, comment ID. Note that this happens inside the default wp_notify_postauthor function, which is a "pluggable" function, meaning that plugins can override it; see Plugin API).
comment_notification_subject 
applied to the mail subject before sending email notifying the post author of a new comment. Filter function arguments: mail subject, comment ID. Note that this happens inside the default wp_notify_postauthor function, which is a "pluggable" function, meaning that plugins can override it; see Plugin API).
comment_notification_text 
applied to the body of the mail message before sending email notifying the post author of a new comment. Filter function arguments: mail body text, comment ID. Note that this happens inside the default wp_notify_postauthor function, which is a "pluggable" function, meaning that plugins can override it; see Plugin API).
cron_schedules 
applied to an empty array to allow a plugin to generate cron schedules in the wp_get_schedules function.
custom_menu_order 
used to activate the 'menu_order' filter.
default_content 
applied to the default post content prior to opening the editor for a new post.
default_excerpt 
applied to the default post excerpt prior to opening the editor for a new post.
default_title 
applied to the default post title prior to opening the editor for a new post.
editable_slug 
applied to the post, page, tag or category slug by the get_sample_permalink function.
explain_nonce_(verb)-(noun) 
allows a filter function to define text to be used to explain a nonce that is otherwise not explained by the WordPress core code. You will need to define specific verb/noun filters to use this. For instance, if your plugin defines a nonce for updating a tag, you would define a filter for "explain_nonce_update-tag". Filter function arguments: text to display (defaults to a generic "Are you sure you want to do this?" message) and extra information from the end of the action URL. In the example here, your function might simply return the string "Are you sure you want to update this tag?".
format_to_edit 
applied to post content, excerpt, title, and password by the format_to_edit function, which is called by the admin menus to set up a post for editing. Also applied to when editing comments in the admin menus.
format_to_post 
applied to post content by the format_to_post function, which is not used in WordPress by default.
manage_edit-${post_type}_columns 
applied to the list of columns to print on the manage posts screen for a custom post type. Filter function argument/return value is an associative array where the element key is the name of the column, and the value is the header text for that column. See also action manage_${post_type}_posts_custom_column, which puts the column information into the edit screen.
manage_link-manager_columns 
was manage_link_columns until wordpress 2.7. applied to the list of columns to print on the blogroll management screen. Filter function argument/return value is an associative list where the element key is the name of the column, and the value is the header text for that column. See also action manage_link_custom_column, which puts the column information into the edit screen.
manage_posts_columns 
applied to the list of columns to print on the manage posts screen. Filter function argument/return value is an associative array where the element key is the name of the column, and the value is the header text for that column. See also action manage_posts_custom_column, which puts the column information into the edit screen. (see Scompt's tutorial for examples and use.)
manage_pages_columns 
applied to the list of columns to print on the manage pages screen. Filter function argument/return value is an associative array where the element key is the name of the column, and the value is the header text for that column. See also action manage_pages_custom_column, which puts the column information into the edit screen.
menu_order 
applied to the array for the admin menu order. Must be activated with the 'custom_menu_order' filter before.
postmeta_form_limit 
applied to the number of post-meta information items shown on the post edit screen.
pre_upload_error 
applied to allow a plugin to create an XMLRPC error for uploading files.
preview_page_link 
applied to the link on the page editing screen that shows the page preview at the bottom of the screen.
preview_post_link 
applied to the link on the post editing screen that shows the post preview at the bottom of the screen.
richedit_pre 
applied to post content by the wp_richedit_pre function, before displaying in the rich text editor.
schedule_event 
applied to each recurring and single event as it is added to the cron schedule.
show_password_fields 
applied to the true/false variable that controls whether the user is presented with the opportunity to change their password on the user profile screen (true means to show password changing fields; false means don't).
terms_to_edit 
applied to the CSV of terms (for each taxonomy) that is used to show which terms are attached to the post.
the_editor 
applied to the HTML DIV created to house the rich text editor, prior to printing it on the screen. Filter function argument/return value is a string.
user_can_richedit 
applied to the calculation of whether the user's browser has rich editing capabilities, and whether the user wants to use the rich editor, in the user_can_richedit function. Filter function argument and return value is true/false if the current user can/cannot use the rich editor.
user_has_cap 
applied to a user's capabilities list in the WP_User->has_cap function (which is called by the current_user_can function). Filter function arguments are the capabilities list to be filtered, the capability being questioned, and the argument list (which has things such as the post ID if the capability is to edit posts, etc.)
wp_handle_upload 
applied to the upload information when uploading a file. Filter function argument: array with elements "file" (file name), "url", "type".
wp_upload_tabs 
applied to the list of custom tabs to display on the upload management admin screen. Use action upload_files_(tab) to display a page for your custom tab (see Plugin API/Action Reference).
media_upload_tabs 
applied to the list of custom tabs to display on the upload management admin screen. Use action upload_files_(tab) to display a page for your custom tab (see Plugin API/Action Reference).

Rich Text Editor Filters

These filters modify the configuration of the rich text editor.

mce_spellchecker_languages 
applied to the language selection available in the spell checker.
mce_buttons, mce_buttons_2, mce_buttons_3, mce_buttons_4 
applied to the rows of buttons for the rich editor toolbar (each is an array of button names).
mce_css 
applied to the CSS file URL for the rich text editor.
mce_external_plugins 
applied to the array of external plugins to be loaded by the rich text editor.
mce_external_languages 
applied to the array of language files loaded by external plugins, allowing them to use the standard translation method (see tinymce/langs/wp-langs.php for reference).
tiny_mce_before_init 
applied to the whole init array for the editor.

Template Filters

This section contains links related to themes, templates, and style files.

locale_stylesheet_uri 
applied to the locale-specific stylesheet URI returned by the get_locale_stylesheet_uri function. Filter function arguments: URI, stylesheet directory URI.
stylesheet 
applied to the stylesheet returned by the get_stylesheet function.
stylesheet_directory 
applied to the stylesheet directory returned by the get_stylesheet_directory function. Filter function arguments: stylesheet directory, stylesheet.
stylesheet_directory_uri 
applied to the stylesheet directory URI returned by the get_stylesheet_directory_uri function. Filter function arguments: stylesheet directory URI, stylesheet.
stylesheet_uri 
applied to the stylesheet URI returned by the get_stylesheet_uri function. Filter function arguments: stylesheet URI, stylesheet.
template 
applied to the template returned by the get_template function.
template_directory 
applied to the template directory returned by the get_template_directory function. Filter function arguments: template directory, template.
template_directory_uri 
applied to the template directory URI returned by the get_template_directory_uri function. Filter function arguments: template directory URI, template.
theme_root 
applied to the theme root directory (normally wp-content/themes) returned by the get_theme_root function.
theme_root_uri 
applied to the theme root directory URI returned by the get_theme_root_uri function. Filter function arguments: URI, site URL.

You can also replace individual template files from your theme, by using the following filter hooks. See also the template_redirect action hook. Each of these filters takes as input the path to the corresponding template file in the current theme. A plugin can modify the file to be used by returning a new path to a template file.

404_template 
archive_template 
You can use this for example to enforce a specific template for a custom post type archive. This way you can keep all the code in a plugin.
attachment_template 
author_template 
category_template 
comments_popup_template 
comments_template 
date_template 
home_template 
page_template 
paged_template 
search_template 
single_template 
You can use this for example to enforce a specific template for a custom post type. This way you can keep all the code in a plugin.
template_include 

Kubrick Filters

These filters were present in the pre-3.0 default theme kubrick.

kubrick_header_color 
applied to the color for the header of the kubrick theme.
kubrick_header_display 
applied to the display option for the header of the kubrick theme.
kubrick_header_image 
applied to the header image file for the kubrick theme.

Advanced WordPress Filters

This section contains advanced filters related to the WordPress queries, rewrite rules, internationalization, and other fundamental WordPress functions.

allowed_redirect_hosts 
applied to the list of host names deemed safe for redirection. wp-login.php uses this to defend against a dangerous 'redirect_to' request parameter
author_rewrite_rules 
applied to the author-related rewrite rules after they are generated.
category_rewrite_rules 
applied to the category-related rewrite rules after they are generated.
comments_rewrite_rules 
applied to the comment-related rewrite rules after they are generated.
create_user_query 
applied to the query used to save a new user's information to the database, just prior to running the query.
date_rewrite_rules 
applied to the date-related rewrite rules after they are generated.
found_posts 
applied to the list of posts, just after querying from the database.
found_posts_query 
after the list of posts to display is queried from the database, WordPress selects rows in the query results. This filter allows you to do something other than SELECT FOUND_ROWS() at that step.
get_editable_authors 
applied to the list of post authors that the current user is authorized to edit in the get_editable_authors function.
gettext 
applied to the translated text by the translation() function (which is called by functions like the __() and _e() internationalization functions ). Filter function arguments: translated text, untranslated text and the text domain. Gets applied even if internationalization is not in effect or if the text domain has not been loaded.
override_load_textdomain
get_meta_sql 
in function WP_Meta_Query::get_sql (which generates SQL clauses to be appended to a main query for advanced meta queries.), applied to the SQL JOIN and WHERE clause generated by the advanced meta query. Filter function arguments: array( compact( 'join', 'where' ), $this->queries, $type, $primary_table, $primary_id_column, $context )
get_next_post_join 
in function get_next_post (which finds the post after the currently-displayed post), applied to the SQL JOIN clause (which normally joins to the category table if user is viewing a category archive). Filter function arguments: JOIN clause, stay in same category (true/false), list of excluded categories.
get_next_post_sort 
in function get_next_post (which finds the post after the currently-displayed post), applied to the SQL ORDER BY clause (which normally orders by post date in ascending order with a limit of 1 post). Filter function arguments: ORDER BY clause.
get_next_post_where 
in function get_next_post (which finds the post after the currently-displayed post), applied to the SQL WHERE clause (which normally looks for the next dated published post). Filter function arguments: WHERE clause, stay in same category (true/false), list of excluded categories.
get_others_drafts 
applied to the query that selects the other users' drafts for display in the admin menus.
get_previous_post_join 
in function get_previous_post (which finds the post before the currently-displayed post), applied to the SQL JOIN clause (which normally joins to the category table if user is viewing a category archive). Filter function arguments: join clause, stay in same category (true/false), list of excluded categories.
get_previous_post_sort 
in function get_previous_post (which finds the post before the currently-displayed post), applied to the SQL ORDER BY clause (which normally orders by post date in descending order with a limit of 1 post). Filter function arguments: ORDER BY clause.
get_previous_post_where 
in function get_previous_post (which finds the post before the currently-displayed post), applied to the SQL WHERE clause (which normally looks for the previous dated published post). Filter function arguments: WHERE clause, stay in same category (true/false), list of excluded categories.
get_users_drafts 
applied to the query that selects the users' drafts for display in the admin menus.
locale 
applied to the locale by the get_locale function.
mod_rewrite_rules 
applied to the list of rewrite rules given to the user to put into their .htaccess file when they change their permalink structure. (Note: replaces deprecated filter rewrite_rules.)
post_limits 
applied to the LIMIT clause of the query that returns the post array.
posts_distinct 
allows a plugin to add a DISTINCTROW clause to the query that returns the post array.
posts_fields 
applied to the field list for the query that returns the post array.
posts_groupby 
applied to the GROUP BY clause of the query that returns the post array (normally empty).
posts_join_paged 
applied to the JOIN clause of the query that returns the post array, after the paging is calculated (though paging does not affect the JOIN, so this is actually equivalent to posts_join).
posts_orderby 
applied to the ORDER BY clause of the query that returns the post array.
posts_request 
applied to the entire SQL query that returns the post array, just prior to running the query.
post_rewrite_rules 
applied to the post-related rewrite rules after they are generated.
root_rewrite_rules 
applied to the root-level rewrite rules after they are generated.
page_rewrite_rules 
applied to the page-related rewrite rules after they are generated.
posts_where_paged 
applied to the WHERE clause of the query that returns the post array, after the paging is calculated (though paging does not affect the WHERE, so this is actually equivalent to posts_where).
posts_join 
applied to the JOIN clause of the query that returns the post array. This is typically used to add a table to the JOIN, in combination with the posts_where filter.
posts_where 
applied to the WHERE clause of the query that returns the post array.
query 
applied to all queries (at least all queries run after plugins are loaded).
query_string 
deprecated - use query_vars or request instead.
query_vars 
applied to the list of public WordPress query variables before the SQL query is formed. Useful for removing extra permalink information the plugin has dealt with in some other manner.
request 
like query_vars, but applied after "extra" and private query variables have been added.
rewrite_rules_array 
applied to the entire rewrite rules array after it is generated.
search_rewrite_rules 
applied to the search-related rewrite rules after they are generated.
the_posts 
applied to the list of posts queried from the database after minimal processing for permissions and draft status on single-post pages.
excerpt_length 
Defines the length of a single-post excerpt.
excerpt_more 
Defines the more string at the end of the excerpt.
post_edit_form_tag 
Allows you to append code to the form tag in the default post/page editor.
update_user_query 
applied to the update query used to update user information, prior to running the query.
uploading_iframe_src (removed since WP 2.5)
applied to the HTML src tag for the uploading iframe on the post and page editing screens.
wp_redirect 
applied to a redirect URL by the default wp_redirect function. Filter function arguments: URL, HTTP status code. Note that wp_redirect is also a "pluggable" function, meaning that plugins can override it; see Plugin API).
wp_redirect_status 
applied to the HTTP status code when redirecting by the default wp_redirect function. Filter function arguments: HTTP status code, URL. Note that wp_redirect is also a "pluggable" function, meaning that plugins can override it; see Plugin API).
redirect_canonical 
Can be used to cancel a "canonical" URL redirect. Accepts 2 parameters: $redirect_url, $requested_url. To cancel the redirect return FALSE, to allow the redirect return $redirect_url
xmlrpc_methods 
applied to list of defined XMLRPC methods for the XMLRPC server.
wp_mail_from 
applied before any mail is sent by the wp_mail function. Supplied value is the calculated from address which is wordpress at the current hostname (set by $_SERVER['SERVER_NAME']). The filter should return an email address or name/email combo in the form "user@example.com" or "Name <user@example.com>" (without the quotes!).
wp_mail_from_name 
applied before any mail is sent by the wp_mail function. The filter should return a name string to be used as the email from name.

Widgets

This section contains filters added by the WordPress Widgets.

widget_archives_dropdown_args 
applied to the arguments passed to the wp_get_archives() function in the WordPress Archives widget.
widget_links_args 
applied to the arguments passed to the wp_list_bookmarks() function in the WordPress Links widget.
widget_pages_args 
applied to the arguments passed to the wp_list_pages() function in the WordPress Pages widget.
widget_tag_cloud_args 
applied to the arguments passed to the wp_tag_cloud() function in the WordPress Pages widget.
widget_text 
applied to the widget text of the WordPress Text widget. May also apply to some third party widgets as well.
widget_title 
applied to the widget title of any user editable WordPress Widget. May also apply to some third party widgets as well.


Admin Bar

This section contains filters added by the Admin Bar added in WordPress 3.1.0.

wp_admin_bar_class 
allows changing the default 'WP_Admin_Bar' class in the _wp_admin_bar_init() function in wp-includes/admin-bar.php.

Further Reading

  • Writing a Plugin - description of how to write a plugin
  • Plugin API - article on how to use filters and actions
  • Plugin API/Action Reference - reference list for Action hooks
  • Plugin Resources - comprehensive list of plugin-related resources
  • WordPress Hooks, a work in progress directory of all of WordPress’ hooks.
  • WordPress Hooks Database, a database of all WordPress' hooks, showing which version they come from, and linking to the source code spots that use them
  • Angsuman's list, a comprehensive listing of WordPress action hooks with documentation and source code location information. It contains all documented and undocumented action hooks in WordPress 2.0.