hunspell

Hunspell is a free, open-source spell checker, morphological analyzer, and hyphenation library designed to support many languages. It originated as a fork of MySpell and was developed to provide Unicode support and better handling of complex word formation. The project is written in C++ and provides both a command-line utility, hunspell, and a library (libhunspell) that can be embedded in applications.

Hunspell uses dictionaries described by .dic files and affix rules in .aff files. The dictionaries list valid base forms and affixes; the engine uses these rules to generate and recognize word forms, check spelling, and perform hyphenation. Its Unicode support enables languages with non-Latin scripts and diacritics. It also supports morphology features through affixes, word formation rules, and multiword expressions implemented in the dictionaries.

Language coverage is broad, with dictionaries available for English, Spanish, French, German, Portuguese, Russian, Hungarian, Turkish, Finnish, Norwegian, Swedish, Danish, Croatian, and many others. Dictionaries and hyphenation patterns are contributed by language communities and third parties, allowing extensive localization.

In practice, Hunspell is used in a variety of software and platforms. It is the default spell checker in LibreOffice and Apache OpenOffice in many configurations, and is also used in Mozilla Firefox and SeaMonkey, Google Chrome and Chromium, among other projects. It is distributed under the LGPL version 2.1 or later, with dictionaries provided under various licenses.