Unicode's Mathematical Monospace block contains a full, separate copy of the Latin alphabet and digits designed to look like fixed-width typewriter characters. This tool maps each letter of your input to that block, so the output is genuine Unicode text — not an image or an installed font — that pastes cleanly anywhere plain text is accepted. The visual "monospacing" is a property of the glyphs themselves, but the app you paste into still renders them with its own font, so actual column alignment can vary slightly between platforms.
Even though these characters come from a "monospace" Unicode block, the app displaying them ultimately decides how wide to render each glyph, so true pixel-perfect alignment isn't guaranteed outside of a genuine monospaced font.
It's purely cosmetic, so avoid it for anything that needs to actually run — code editors, terminals, and compilers expect standard ASCII characters and won't treat these look-alikes as the real letters or digits.
Yes — digits 0 through 9 have their own monospace Unicode forms too, so numbers convert alongside letters in the same style.