Scottish Gaelic Spellchecker will add a Scots Gaelic spell-checking extension to your local version of LibreOffice.
It contains over 10,000 roots and rules that handle things like lenition, initial n- t- h-, endings such as -sa, -eigin and so on. As a result, it will spellcheck much more than 10,000 words, making it by far the biggest Gaelic spellchecker to date. Please note the following:
This is an open spellchecker. Whichever spelling school you follow, there are gaps and inconsistencies in all of them. Therefore this tool will accept any spelling that is correct in both traditional systems and GOC. For example, it will accept mór and mòr, doras and dorus and dàinig and tàinig. It's up to you to pick a system and follow it.
If you already have Check spelling as you type activated in LibreOffice (i.e. you see red lines appear under mis-spelled words), you usually need to do the following to spellcheck Gaelic:
Ok. You can now see the suggestions for mis-spelled Gaelic words by right-clicking on an underlined word.
If you're using the Gaelic version (i.e. all LibreOffice menus are in Gaelic already), you usually don't have to do any of that to get the spellchecker to work. If you're still using LibreOffice in English, why not give the Gàidhlig version a try?