Mediocre results.
*New words you add to dictionary are never offered as correction.
*Many times there's no proper correction for simple typing mistake, like changing the order of two letters in a word - the suggestions are weird and irrelevant.
TL;DR - barely more useful than Firefox' (horrible) built-in speller.

Great :)

Nice To you

Grammar and Spell Checker - LanguageTool: A Review

LanguageTool is a free grammar and spell checker that helps users improve their writing by detecting errors and providing suggestions for improvement. It is available as a browser extension, add-on for various software, and a desktop application. Here is a review of LanguageTool based on user feedback and information from the search results:

Features and Functionality:

LanguageTool is designed to check text for spelling and grammar problems across various platforms, including web browsers, word processors, and email services

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It can detect many errors that a simple spell checker cannot, such as grammar issues, commonly confused words, and punctuation oversights
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The tool offers style suggestions, including synonym replacements for overused words, concise rephrasing of wordy sentences, and formal alternatives to commonly used expressions
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It supports more than 25 languages, including English, German, Spanish, French, Dutch, Polish, and Russian
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unico problema que encontei foi trocar meu nome pseudo nome rodsanluc para rodoanel sem questionar e aqui não funciona. teste obrigatorio

Отличная проверка правописания, рекомендую.

It's a very useful tool for spell checking but I'm very sad that it's not available in Hungarian. I know it's a difficult task to include all languages but I still expected all EU countries to be available. Disappointed.
Still, the app works as advertised when I'm using English.

good

Отличное и очень удобное дополнение.