Ask HN: When and how should I release my open source tool?

I'm very new to the open source world, but I built a command line tool for myself that I think other people could use too. I'm in the process of building a few new features that I think would be helpful to people (and to myself). Should I hold off on telling people about it until I finish those features? Or should I market it and then see which features people want? How do I find out what makes a tool "good" for other people?

Also, what's the correct way to tell people about a tool like this?