Ispell is a spellchecker for Unix that supports most Western languages. It offers several interfaces, including a programming interface for use by editors such as emacs. Unlike GNU Aspell, ispell only suggests corrections based on a Damerau-Levenshtein distance of 1; it does not attempt to derive more distant corrections based on pronunciation rules. Ispell has a long history that goes back to a program that was originally written in 1971 in the assembly language PDP-10 by RE Gorin, and later ported to the C programming language and expanded to many others. It is currently maintained by Geoff Kuenning. The generalized affix description system introduced by Ispell since then has been imitated by other spell checkers like MySpell.
Like most computerized spell checkers, ispell acts by reading an input file, word for word, stopping when a word is not found in its dictionary. Ispell then tries to generate a list of possible corrections and presents the wrong word and any suggestions to the user, who can then choose a correction, replace the word with a new one, leave it unchanged or add it to the dictionary.
Ispell pioneered the idea of a programming interface, which was originally intended for use by emacs. Other applications have since used the function of adding the spelling correction to its own interface and GNU Aspell has adopted the same interface, so that it can be used with the same set of applications.
There are ispell dictionaries for the most widely spoken western languages.
Ispell is available under a specific open source license.
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