Most popular variants of the header value (we only show this when there's just a bunch of variants):

Purely informational and non-standard header initially established in memory of a popular fantasy author Terry Pratchett. Counterintuitively for most IT people, the most frequently seen value GNU is not related to the open-source GNU project, but rather is a sophisticated telegraph code originating from Pratchett's "Discworld" cult series.


We have seen 47 websites setting the X-Clacks-Overhead HTTP header and 2 unique values of this header.