Writefull is an app that provides feedback on your writing by checking your text against databases of correct language. The databases used are Google Books, Google Scholar, Google News, and Google Web.
You can use Writefull in any writing tool from MS Word to Gmail. Simply select a piece of text, hit the short-key to activate the Writefull popover, and choose one of its options.
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More information about Writefull in Spanish by Juan Diego Polo: