From the article:

"It goes without saying (although I say it anyway on that page), but don't enter a password you currently use into any third-party service like this! I don't explicitly log them and I'm a trustworthy guy but yeah, don't."

Safe: probably. Good practice: no.

Hehe, I was just about to build something similar. I like the extra touch of it not even being served over https.

Also the option to test another password is nice, and the unsatisfied curiosity you're left with if you go down that route.

worth reading the T&Cs for a chuckle

I should have read that before agreeing to it...

Well, I better get prepped to fight the Estatis Inc. Retaliatory Creature to retain full ownership of my soul. Thanks for the heads up.

If you only have one password to try, I'd say you have more important issues to tackle. Install a password manager, start using generated passwords, and stop using 'your password'.

Well, in that case, “your password” might be the only one you have – the one use for your password manager.

Well, in that case, it should already be something that's staggeringly improbable to be used by anyone else, and for your use, you should never ever ever send this password through any network interface at all (including this check page).

salt "your password" with https://www.passwordcard.org/en

"Pick a password length. Eight is pretty secure and usually acceptable." Wait, what? Unless you're suggesting that I append this to a password.

you can choose any area of the card, say 5 letters and a few keywords.

Disclosing a password weakens that password, since passwords only work when they are kept private.

You're probably okay, but Troy probably has the query stored somewhere, hence, he doesn't recommend that.

It is much, much safer to download the data and search for your passwords from inside the local copy of the data, and that's exactly what I'm gonna do later tonight.