I use unique passwords for everything, and most of them I do not write down. I just let Keychain manage them.
As I'm sure you know, "i hacked your email, give me $800 in bitcoin" emails are all the rage these days. I know they are fake, these passwords are not my computer passwords or email account passwords. They are from online accounts, and I'd like to know WHICH online accounts.
So it would be very handy if I could look at the password, search keychain, and use that to determine which website I have an account on, had their security breached.
Best Answer
In the absence of any better suggestions ;)...
Unlock Safari > Preferences > Passwords.
Then select all entries (select one first, to bring the right area into focus, then select all entries by pressing the cmd+A keyboard keys), which will make all passwords visible (usually displayed as dots. Earlier versions of Safari need the "Show passwords for selected websites" box ticked).
Now click on the "Password" tab, to sort them alphabetically. Look for your password.
As bonus, all sites with the same password will also be displayed underneath each other.