This is a non-technical question, but certainly relevant for the TCS community. If considered inappropriate, feel free to close.

The Complexity Zoo webpage (http://qwiki.stanford.edu/index.php/Complexity_Zoo) has certainly been of great service to the TCS community over the years. Apparently it is down since quite a while. I was wondering, if someone is still maintaining it, if it has moved, if there is a backup server, or if there are other plans to preserve this wonderful database of complexity classes, their relationships and citations to relevant publications. If not, are there comparable webpages that could be used as a replacement?

UPDATE (Aug 1, 2012): The Zoo is back online, and Scott is looking for people volunteering to mirror it to avoid any future outages.

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    $\begingroup$ Have you tried to email any of the zookeepers? $\endgroup$ Commented Jul 25, 2012 at 13:29
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    $\begingroup$ @TsuyoshiIto: I see the concern, but I think asking the relevant community about preserving a relevant community resource is not inappropriate. Anyway, I will certaintly accept a ballot to close the question. $\endgroup$ Commented Jul 25, 2012 at 13:36
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    $\begingroup$ A question (and warning sign to the community) about the status of a valuable resource seems strictly more pertinent a question to the study of theoretical computer science as one about Alan Turing documentaries or Funny TCS-related papers etc. Of course, at such a time as the Zoo is found to be in good working shape, it would also be appropriate to flag the question as "too localized". $\endgroup$ Commented Jul 25, 2012 at 14:50
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    $\begingroup$ think that the use of comments to argue whether a question is ontopic or not is not a good use of stackexchange yet it constantly happens here in the TCS stackexchange. it seems the community here is a little overzealous as gatekeepers compared to other stackexchanges. its basically a meta issue. just use the other mechanisms-- voting, closing questions in extreme cases, the meta section. $\endgroup$
    – vzn
    Commented Jul 25, 2012 at 18:03
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    $\begingroup$ I know that I'm a little late to the party here, but to be completely honest, questions like this keep me coming back here. We're a community, and this is relevant to me. Besides, it's a soft question. Without soft questions this site can be really dry. $\endgroup$ Commented Jul 26, 2012 at 4:38

3 Answers 3


I cannot remark on whether the Zoo has a continuous existence on the web or elsewhere. However, there are still some proto-Zoo and Zoo-derived resources available on the web.

Other sources on the net seem to be links to the first (or to the URL to the stanford.edu subsite), or pieces of the second.

It is worth noting that the entire qwiki.stanford.edu subsite seems to have disappeared, and that google searches for "qwiki", with or without specifying "stanford", either yields references to a multimedia product launched in January of last year, or produces the typical spoor of SEO companies trying to leach off of online resources.


Scott Aaronson just reported that the Complexity Zoo is down because the graduate student that was hosting it has graduated.

To get the Complexity Zoo working again, we need someone to host and a copy of the site.

  • $\begingroup$ What would that take ? $\endgroup$ Commented Jul 31, 2012 at 17:44

Now that the site is again up and running, I guess anyone can download most (?) of the data (machine-readable source code, with full edit history) as follows:

  • Go to http://qwiki.stanford.edu/index.php/Special:Export
  • Enter Computational Complexity in the field "Add pages from category", click "Add" — double-check that all relevant pages are now listed in the text box
  • Un-check "Include only the current revision"
  • Click "Export"

It produces a fairly large file, approx. 160 MB.

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    $\begingroup$ there's some awesome graph mining that might be worth doing on this :) $\endgroup$ Commented Aug 1, 2012 at 22:28

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