WordPress hook before inserting post into database

Available actions:

1. pre_post_update – Runs just before a post or page is updated.
2. publish_post – Runs when a post is published, or if it is edited and its status is “published”.
3. save_post – Runs whenever a post or page is created or updated, which could be from an import, post/page edit form, xmlrpc, or post by email.
4. wp_insert_post – Same as save_post, runs immediately afterwards.

More info: Plugin API/Action Reference

Usage:

<?php
add_action('action_name', 'callback_name');