These are letters, not a font
A font lives on the device that displays the text. Paste text styled with a font into somewhere else and the styling is gone, because the other place has its own font.
What this tool produces is different. Unicode contains separate characters for bold A, italic A, script A and about a dozen more, added for mathematicians who need to distinguish a vector from a scalar. Copy one and you are copying a character, the same way you copy é or ⌘. That is why the shape survives a paste into a bio field that offers no formatting at all.
What you give up
Search stops working. 𝒮𝒸𝓇𝒾𝓅𝓉 and Script are unrelated characters as far as any search box is concerned. Someone looking for your name, your business or your hashtag will not find the decorated version.
Screen readers struggle. Depending on the software, a bold-script sentence is read out character by character, announced by Unicode name, or skipped in silence. If the words carry meaning rather than decoration, that meaning is lost to anyone using one.
Hashtags break. Most platforms only recognise a hashtag made of ordinary letters, so a decorated tag is plain text that happens to start with a hash.
The practical rule: decorate a display name or one accent line, and keep the parts people need to search, read or tap in ordinary letters.
Where it renders and where it breaks
The characters are standard, but a device only shows them if its font has drawings for them. When it does not, you get an empty box. Modern phones and desktops handle the mathematical alphabets well; older Android builds, some smart TVs and a few embedded browsers do not.
Circled and squared letters are the safest, followed by bold and italic. Fraktur and the doubled outline style are the ones most likely to fall back. Test on a phone before committing to a name you will keep.
Before using one in a username
Some services accept these characters in a display name but not in the handle you log in with. Others normalise them silently, so the fancy text you typed is stored as plain letters. And a name people cannot type is a name they cannot mention or tag.
Nicknames on gaming and chat platforms are the place where this works well. Legal names, business listings and anything a customer might need to search for are the places where it does not.
Turning decorated text back to plain
The other tab reverses the mapping. Paste something you found online — a profile name you want to copy, a heading full of decorated letters, a strikethrough comment — and it comes back as ordinary characters you can search for, edit or store.
Strikethrough and underline work slightly differently from the others: they add an invisible combining mark after each letter rather than replacing it. Stripping those marks leaves the original text untouched.
Some styles cannot give the capitals back. Small caps, squared letters and superscript use one glyph for both cases — wholly or in a few positions — so XYZ returns as xyz.