Some technical details for those interested:

Topic tags use the PostgreSQL data type ltree to support having a hierarchy with sub-tags and such (groups also use this). Tags are stored in the database in an array column with ltree values. So the actual data for a topic's tags might look something like this: {programming,bugs,some_tag,parent_tag.sub_tag}.

The site's code uses the SQLAlchemy library to interact with the database, but it doesn't support arrays of ltree (or at least this version doesn't), so I had to write some custom handling for them to convert between Python types and the PostgreSQL representation. The error was happening when reading the value out of the database, because null is escaped when stored (to store the string "null" and not a literal null value), and the data looks more like this: {some_tag,"null",another}.

I hadn't accounted for the possibility that a string could be escaped in the value like that. The PostgreSQL docs mention it, but almost all of these possibilities aren't valid in tags (or ltree values) anyway:

The array output routine will put double quotes around element values if they are empty strings, contain curly braces, delimiter characters, double quotes, backslashes, or white space, or match the word NULL.

So it wasn't really anything "dangerous"—it was being stored properly, but caused an error when reading it back out. Funny, ironic (and kinda embarrassing) in the context this came up though.

I'm seeing the same thing. Was able to navigate directly to ~tildes to find this post. I guess we'll see if this comment goes through.

Oh I guess it's just the homepage then. I found this post by googling "is tildes.net down".

I can access some groups, but not other(s?), such as ~comp.

Same here. I only found this because I was persistent in looking for either redundant confirmation or finding non-tildes locations to ask others about status.

Fixed