(#fzmmn2q) @zvava@twtxt.net Good question. This is the spec, I think:

https://twtxt.dev/exts/metadata.html#nick

It doesn’t say much. 🤔

In the wild, I’ve only seen “traditional” nick names, i.e. ASCII 0x21 thru 0x7E.

My client removes anything but r'[a-zA-Z0-9]' from nick names.

(#fzmmn2q) @zvava@twtxt.net @movq@www.uninformativ.de I’m not entirely sure about the spaces, but maybe they were omitted to simplify parsing of mentions in the form of @<nick url>. If the next token after the @<nick does not look like a URL, it’s not a mention but regular text. This is just wild guessing, though.

Looking at the regex and tests in the original twtxt reference implementation seems to confirm that theory in the sense as it relies on whitespace as the delimiter:

https://lyse.isobeef.org/tmp/screenshot-2025-09-17-21-30-25.png

Another thing about nicks is that the original twtxt reference implementation converts nicks to all lowercase:

https://lyse.isobeef.org/tmp/screenshot-2025-09-17-21-20-39.png

You probably know this already, the original twtxt file format specification can be found here: https://twtxt.readthedocs.io/en/latest/user/twtxtfile.html

As for extensions, I don’t know of anything outside of twtxt.dev that has actually been (partially) implemented. However, there is also the issue tracker of the official reference implementation. You might wanna dig through that. For example, there is an alternative suggestions of multiline messages: https://github.com/buckket/twtxt/issues/157