On-Topic: Anything that good hackers would find interesting. That includes more than hacking and startups. If you had to reduce it to a sentence, the answer might be: anything that gratifies one's intellectual curiosity.

Off-Topic: Most stories about politics, or crime, or sports, or celebrities, unless they're evidence of some interesting new phenomenon. Videos of pratfalls or disasters, or cute animal pictures. If they'd cover it on TV news, it's probably off-topic.

In Submissions

Please don't do things to make titles stand out, like using uppercase or exclamation points, or saying how great an article is. It's implicit in submitting something that you think it's important.

Please submit the original source. If a post reports on something found on another site, submit the latter.

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.

If the title includes the name of the site, please take it out, because the site name will be displayed after the link.

If the title contains a gratuitous number or number + adjective, we'd appreciate it if you'd crop it. E.g. translate "10 Ways To Do X" to "How To Do X," and "14 Amazing Ys" to "Ys." Exception: when the number is meaningful, e.g. "The 5 Platonic Solids."

Otherwise please use the original title, unless it is misleading or linkbait; don't editorialize.

If you submit a video or pdf, please warn us by appending [video] or [pdf] to the title.

Please don't post on HN to ask or tell us something. Send it to hn@ycombinator.com.

Please don't delete and repost. Deletion is for things that shouldn't have been submitted in the first place.

Don't solicit upvotes, comments, or submissions. Users should vote and comment when they run across something they personally find interesting—not for promotion.

In Comments

Be kind. Don't be snarky. Converse curiously; don't cross-examine. Edit out swipes.

Comments should get more thoughtful and substantive, not less, as a topic gets more divisive.

When disagreeing, please reply to the argument instead of calling names. "That is idiotic; 1 + 1 is 2, not 3" can be shortened to "1 + 1 is 2, not 3."

Please don't fulminate. Please don't sneer, including at the rest of the community.

Please respond to the strongest plausible interpretation of what someone says, not a weaker one that's easier to criticize. Assume good faith.

Eschew flamebait. Avoid generic tangents. Omit internet tropes.

Please don't post shallow dismissals, especially of other people's work. A good critical comment teaches us something.

Please don't use Hacker News for political or ideological battle. That tramples curiosity.

Please don't comment on whether someone read an article. "Did you even read the article? It mentions that" can be shortened to "The article mentions that".

Please don't pick the most provocative thing in an article or post to complain about in the thread. Find something interesting to respond to instead.

Throwaway accounts are ok for sensitive information, but please don't create accounts routinely. HN is a community—users should have an identity that others can relate to.

Please don't use uppercase for emphasis. If you want to emphasize a word or phrase, put *asterisks* around it and it will get italicized.

Please don't post insinuations about astroturfing, shilling, brigading, foreign agents, and the like. It degrades discussion and is usually mistaken. If you're worried about abuse, email hn@ycombinator.com and we'll look at the data.

Please don't complain that a submission is inappropriate. If a story is spam or off-topic, flag it. Don't feed egregious comments by replying; flag them instead. If you flag, please don't also comment that you did.

Please don't complain about tangential annoyances—e.g. article or website formats, name collisions, or back-button breakage. They're too common to be interesting.

Please don't comment about the voting on comments. It never does any good, and it makes boring reading.

Please don't post comments saying that HN is turning into Reddit. It's a semi-noob illusion, as old as the hills.