This tool maps your text onto Unicode's "Mathematical Script" block, a set of flowing, cursive-style letterforms originally intended for handwritten-style variables in mathematical notation. Because Facebook's post and comment boxes accept any Unicode character, pasting script text there displays the flowing style without needing any special formatting support from Facebook itself. A handful of uppercase letters (B, E, F, H, I, L, M, R) and a few lowercase ones (e, g, o) use separate, older Unicode script symbols rather than the newer block, since those specific glyphs were standardized earlier — this tool maps them correctly so the whole alphabet stays visually consistent.
Yes, as long as the reader's device has a font installed that includes these Unicode math-script code points, which nearly all modern phones and browsers do — very old devices may show blank boxes instead.
Letters like B, E, F, H, I, L, M, and R use separate legacy Unicode script symbols instead of the newer math-script block, because those particular glyphs were standardized earlier — this tool maps them to the correct legacy code point so they match visually.
Facebook restricts Page and profile names to a limited character set in many cases, so styled Unicode is more reliable in bios, posts, and comments than in the name field itself.