The CheckUser interface currently surfaces user agents when listing users or edits, but there's no way to search by user agent. It would be nice if you could click on a listed user agent and it would then show you all users or edits performed by that user agent.
This may be an expensive query, so we may have to introduce a new database column with hashed user agents that could be used as an index. This would preclude us from being able to do wildcard or prefix searches, however, (for example with a text field) but in almost all cases, the user will want to search for a specific user agent anyway, so I think that's a decent trade-off.
We will need to add one or more indexes to the table for this.
There will be a drop-down menu that lets you select IP address, Username or User agent for the check.