Analyzing HN moderation & censorship

Published 2017-09-13 on Drew DeVault's blog

Hacker News is a popular “hacker” news board. One thing I love about HN is that the moderation generally does an excellent job. The site is free of spam and the conversations are usually respectful and meaningful (if pessimistic at times). However, there is always room for improvement, and moderation on Hacker News is no exception.

For some time now, I’ve been scraping the HN API and website to learn how the moderators work, and to gather some interesting statistics about posts there in general. Every 5 minutes, I take a sample of the front page, and every 30 minutes, I sample the top 500 posts (note that HN may return fewer than this number). During each sample, I record the ID, author, title, URL, status (dead/flagged/dupe/alive), score, number of comments, rank, and compute the rank based on HN’s published algorithm. A note is made when the title, URL, or status changes.

The information gathered is publicly available at (sorry about the stupid domain, I just picked one at random). You can search for any post here going back to 2017-04-14, as well as view recent title and url changes or deleted posts (score>10). Raw data is available as JSON for any post at Feel free to explore the site later, or its shitty code. For now, let’s dive into what I’ve learned from this data.

Tools HN mods use

The main tools I’m aware of that HN moderators can use to perform their duties are:

  • Editing link titles or URLs
  • Artificially influencing story rank
  • Deleting posts
  • Detaching off-topic or rulebreaking comment threads from their parents
  • Shadowbanning misbehaving users

There are also automated tools for detecting spam and voting rings, as well as automated de-emphasizing of posts based on certain secret keywords and controls to prevent flamewars. I don’t yet have enough insight into these tools to tell you more about how they work, but I can share what I’ve learned of the others.

Here’s an example of a fairly common moderator action:

This post had its title changed at around 09-11-17 12:10 UTC, and had the rank artificially adjusted to push it further down the front page. We can tell that the drop was artificial just by correlating it with the known moderator action, but we can also compare it against the computed base rank:

Note however that the base rank is often wildly different from the rank observed in practice; the factors that go into adjusting it are rather complex. We can also see that despite the action, the post’s score continued to increase, even at an accelerated pace:

This “title change and derank” is a fairly common action - here are some more examples from the past few days:

Betting on the Web - Why I Build PWAs

Silicon Valley is erasing individuality

Chinese government is working on a timetable to end sales of fossil-fuel cars

Users can change their own post titles, which I’m unable to distinguish from moderator changes. However, correlating them with a strange change in rank is generally a good bet. Submitters also generally will edit their titles earlier rather than later, so a later change may indicate that it was seen by a moderator after it rose some distance up the page.

I also occasionally find what seems to be the opposite - artificially bumping a post further up the page. Here’s two examples: 15213371 and 15209377. Rank influencing in either direction also happens without an associated title or URL change, but automatically pinning such events down is a bit more subtle than my tools can currently handle.

Moderators can also delete a post or indicate it as a dupe. The latter can be (and is) detected by my tools, but the former is indistinguishable from the user opting to delete posts themselves. In theory, posts that are deleted after the author is no longer allowed to could be detected, but this happens rarely and my tools don’t track posts once they get old enough.


The users have some moderation tools at their disposal, too - downvotes, flagging, and vouching. When a comment is downvoted, it is moved towards the bottom of the thread and is gradually colored grayer to become less visible, and can be reversed with upvotes. When a comment gets enough flags, it is removed entirely unless you have showdead enabled in your profile. Flagged stories are moved to the bottom of the ranked posts even if you have showdead enabled, but can be seen in /new. Flagging can be reversed with the vouch feature, but flagged stories are very infrequently vouched back into existence.

Note: detection of post flagged status is very buggy with my tools. The API exposes a boolean for dead posts, so I have to fall back on scraping to distinguish between different kinds of dead-ness. But this is pretty buggy, so I encourage you to examine the post yourself when browsing my site if in doubt.

Are these tools abused for censorship?

Well, with all of this data, was I able to find evidence of censorship? There are two answers: yes and maybe. The “yes” is because users are definitely abusing the flagging feature. The “maybe” is because moderator action leaves room for interpretation. I’ll get to that later, but let’s start with flagging abuse.

Censorship by users

The threshold for removing a story due to flags is rather low, though I don’t know the exact number. Here are some posts whose flags I consider questionable:

Harvey, the Storm That Humans Helped Cause (23 points)

ES6 imports syntax considered harmful (12 points)

White-Owned Restaurants Shamed for Serving Ethnic Food (33 points)

The evidence is piling up – Silicon Valley is being destroyed (27 points)

A good place to discover these sorts of events is to browse hnstats for posts deleted with a score >10 points. There are also occasions where the flags seem to be due to a poor title, which is a fixable problem for which flagging is a harsh solution:

Poettering downvoted 5 (at time of this writing) times

Germany passes law restricting free speech on the internet

The main issue with flags is that they’re often used as an alternative to the HN’s (by design) lack of a downvoting feature. HN also gives users no guidelines on why they should flag posts, which mixes poorly with automated removal of a post given enough flags.

Censorship by moderators

Moderator actions are a bit more difficult to judge. Moderation on HN is a black box - most of the time, moderators don’t make the reasoning behind their actions clear. Many of their actions (such as rank influence) are also subtle and easy to miss. Thankfully they are often receptive to being asked why some moderation occurred, but only as often as not.

Anecdotally, I also find that moderators occasionally moderate selectively, and keep quiet in the face of users asking them why. Notably this is a problem for paywalled articles, which are against the rules but are often allowed to remain.


I should again emphasize that most moderator actions are benign and agreeable. They do a great job on the whole, but striving to do even better would be admirable. I suggest a few changes:

  • Make a public audit log of moderation activity, or at least reach out to me to see what small changes could be done to help improve my statistics gathering.
  • Minimize use of more subtle actions like rank influence, and when used,
  • More frequently leave comments on posts where moderation has occurred explaining the rationale and opening an avenue for public discussion and/or appeal.
  • Put flagged posts into a queue for moderator review and don’t remove posts simply because they’re flagged.
  • Consider appointing one or two moderators from the community, ideally people with less bias towards SV or startup culture.

Hacker News is a great place for just that - hacker news. It has been for a long time and I hope it continues to be. Let’s work together on running it transparently to the benefit of all.