Unlike XML and UML, there's just less of a market for GUI-like editors for JSON?
Something that would also be nice, if anyone comes up with such a beast would be the ability to edit a multi-record json file... effectively each line is a single JSON, and an LF at the end of each line/record. I've used this structure a few times. Given that JSON will typically encode special characters allowing for single-line representation by default, it's worked really well, especially combined with gzip as a stream for archiving data.
If anyone knows what that program was, would love to find it again.
Tweeted it... It's funny, but I often use twitter to tweet about stuff, just so that I can find them later.
Opening a one-line JSON file of a few MB in Emacs can be painful. The editor struggles to handle the long line and the matching-parenthesis-highlighter runs its stack machine down the whole length looking for the closing delimiter.
There are ways to avoid this, like pretty-printing the JSON across multiple lines, or forcing fundamental-mode when large files are opened, but I still haven't set these up as default.
I believe the question was about good editors for json documents.