Warning
| Design of xkcd.com | Links • Tagline • Header text • Comic • Title text • Footer comics • Feeds • Comics I enjoy • Other things • Warning • Bitcoin address • Footnote • License and copyright |

The warning on xkcd served as a humorous advisory message to users about the contents of the comics. It was originally added to xkcd.com before April 8th, 2006, but it was removed on September 12th, 2016 after more than a decade. It used to appear between Randall's list of "Comics I Enjoy" and the footnote. It stated:
- Warning: this comic occasionally contains strong language (which may be unsuitable for children), unusual humor (which may be unsuitable for adults), and advanced mathematics (which may be unsuitable for liberal-arts majors).
Removal of the warning[edit]
On September 12, 2016, the comic 1732: Earth Temperature Timeline was published and garnered attention from a much wider audience compared to other xkcd comics. Four hours after its release, the warning, along with the previous footnote, were both removed from the site. While a new footnote was added 22 days later, the warning never came back. This new footnote did not include a reinstatement of the original warning message.
On the explain xkcd wiki, it was speculated that the removal of the warning and the footnote was likely a result of the comic's sudden surge in popularity, to ensure that new fans were not deterred by the messages. However, on a Slate article, Randall said he removed it to avoid inciting rivalry:
As a longtime reader of xkcd—and as an English major—I used to chuckle at the warning when I saw it. [...] When I asked Munroe this week why he took it down, he said he’s less worried about offending liberal arts majors than he is about encouraging others in his field who might genuinely look down on other majors.—Marissa Martinelli, xkcd Creator Randall Munroe on the Joys of Overthinking Everything, Slate, September 6, 2019.
I get along with almost everyone I meet who did physics, but I think the flaw we have is that we think we could do everyone else’s field as well if we tried. That attitude has done a little bit more harm than good. It’s nice to have a friendly rivalry, but sometimes that rivalry is only going in one direction, and then maybe it’s not really a rivalry. Maybe you’re just being a jerk. I’m trying not to be a jerk.—Randall Munroe, xkcd Creator Randall Munroe on the Joys of Overthinking Everything, Slate, September 6, 2019.