1. Criteria for health in online communities: users are sincere and extend goodwill towards each other when they discuss topics. Many users (more than a tiny minority) contribute original ideas, personal stories and evidence of things they make. There is some effort required to contribute but members are incentivized to try by the anticipated responses and reactions of other members. Moderation is predictable and is emotionally intelligent. A critical mass of users are mature enough that norms don’t quickly change, and there is no mechanism a small minority can use to be over-represented when administration considers the wishes of the community (i.e. the Metafilter problem.) The community does not believe that its comments are the main attraction to the site. This isn’t a complete list.
2. How the criteria differs from offline community health: online communities are mostly discussion whereas offline communities work together, share meals, and so on, so it’s vital for the discussion to be high quality online in order for the community to be healthy. Offline communities have greeting and parting rituals that shape them.
3. How HN exemplifies healthy or unhealthy behaviors: HN mostly exemplifies healthy behaviors. There is a minority of users who are too immature and inexperienced to make valuable contributions, and a smaller minority who are antisocial. This percentage doesn’t seem to be increasing quickly, though. A substantial number of HN users believe comments are the main draw to the site, which is an unhealthy mindset to the degree those users are willing to let the quality of the links and text posts degrade.
4. Behaviors of my own that contribute: I try to extend goodwill towards users and encourage discussion of particulars, rather than fighting over general statements. On the other hand, I have a tendency to participate in inconsequential/creativity-free conversations that need to stay below a threshold to continue to attract users who have more to offer. I also downvote a lot of comments that attack other users or write unhinged, insubstantial polemics.
5. How I got into HN: I came here from a Paul Graham essay in 2008-2009 (different username.) He had a link to HN on his personal site. At the time, I was developing heavily in Rails and learned a lot from the Ruby-oriented and JS framework articles.
6. Who introduced me: See above. I didn’t know another HN reader personally for years, or at least didn’t know whether I knew one.
7. What makes me stay: the links and Show HN are interesting. Ultimately, good content drives good discussion.