The Bible source text was taken from the Pure Cambridge Edition at the site bibleprotector.com. The pronunciation marks were added based on The Oxford self-pronouncing Bible published in 1897. For reference this site's source Bible text is available, but that file is designed for internal use and not for direct reading.
To crosscheck with offsite sources you can get a Bible Protector text file and an archive.org scan of an 1897 Bible. Please use the Contact page if you find any differences between those files and the text you see on BibleStudy.tools.