There's nothing wrong letting people know about a useful tool that they can take advantage of. It is not a promotion. It is distribution.
From the guidelines
> Please don't use HN primarily for promotion. It's ok to post your own stuff part of the time, but the primary use of the site should be for curiosity.
At least be clear about the self-promotion.
Yes, to me this is the only thing objectionable about the GP’s comment.
Just be transparent. If anything it might provoke further interest and discussion too.