Whether a Unicode character works somewhere depends on three independent layers: the character must exist in the standard, the font must have a glyph for it, and the application must accept it. A failure at any layer looks like "it does not work", and each has a different cause and a different fix.
Layer one: the standard
A character either is or is not encoded. Everything on this site is. This layer is almost never the problem, but it sets the ceiling — a character that does not exist cannot be made to work.
Layer two: font coverage
No font covers all of Unicode. Your device falls back through several fonts looking for a glyph, and shows a box when none has one. Coverage is thinnest for recent additions and for supplementary-plane characters above U+FFFF. This is why the same text renders differently on two devices with no change to the text itself.
Layer three: application rules
Apps decide what they accept. A service may allow a character in a bio and reject it in a username, normalise input on save, or filter scripts it does not expect. These rules are undocumented, vary by field, and change with releases. Most reports of a style "no longer working" are this layer.
Why we publish no compatibility table
A table claiming a style works on a given platform would need testing on that platform, on current app versions, in the specific field, on representative devices — and re-testing whenever anything changes. Without that, such a table is a guess presented as a fact. We publish character coverage, which we compute and can demonstrate, and we say plainly that platform behaviour is something we have not tested.
Testing it yourself
Use a short string. Test the exact field, not a similar one. Save and then view the result as a visitor would, since edit views and published views can differ. Check on a phone as well as a computer. Record what you tested and when, because the answer has a shelf life.
Reducing risk
Prefer older, widely supported ranges: bold, italic, small caps, the basic geometric shapes. Avoid supplementary-plane characters and long combining sequences where reliability matters. Keep a plain-text fallback for anything that has to be read or found.
References
Related tools and guides
Last updated September 2026 · Editorial policy · How we verify Unicode claims