WordPress.org

This plugin allows you to offer 'Did you mean' spelling suggestions for queries on your site. By inserting a single line of code into your theme file, your site can have the same powerful spell checking employed by the major search engines.

ProperSpell's unparalleled spell checking service is based on the actual usage of words and phrases, as opposed to a dictionary, so it can suggest common spellings for proper nouns and popular terms. It can also determine the context of a search term in order to provide intelligent search alternatives.

In order to use this service, you must first obtain API keys from http://www.properspell.com.