The text tools work on a paste in the browser. Nothing is uploaded, and there is no account. They do not open or save a file.
Text Diff marks lines as unchanged, removed, or added. A small edit inside a line marks that whole line. Word Counter splits on whitespace as you type. Case Converter shows upper case, lower case, title case, and sentence case under English rules, and it leaves the box you typed in unchanged. Slug Generator builds a lowercase hyphenated path segment and drops letters that do not become a to z.
Lorem Ipsum Generator repeats a fixed list of placeholder sentences. It is not a translation. Remove Duplicate Lines keeps the first copy of a line. Sort Lines orders lines alphabetically, so 10 sorts before 2. Find and Replace treats the find text as literal unless you tick the regular expression option.
Email Validator sits with these text tools because it judges a string. The email check is syntax only. It does not prove that a mailbox exists, and it does not look up an MX record. The directory also lists that page under Media and Design.
Tools
Read the privacy page for what each check sends.