hat to Submit
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, 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 adding a parenthetical remark 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.

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

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 begins with a number or number + gratuitous 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.

Please don't post on HN to ask or tell us something. Instead, please send it to hn@ycombinator.com. Similarly, please don't use HN posts to ask YC-funded companies questions that you could ask by emailing them.

Please don't submit so many links at once that the new page is dominated by your submissions.

In Comments

Be kind. Don't be snarky. 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 respond to the strongest plausible interpretation of what someone says, not a weaker one that's easier to criticize. Assume good faith.

Eschew flamebait. Don't introduce flamewar topics unless you have something genuinely new to say. Avoid unrelated controversies and generic tangents.

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. It destroys intellectual curiosity, which the site exists for.

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

Throwaway accounts are ok for sensitive information, but please don't create them routinely. On HN, 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 impute astroturfing or shillage. That degrades discussion and is usually mistaken. If you're worried, email us 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 comment about the voting on comments. It never does any good, and it makes boring reading.

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