On the privileges page for creating tags it says:

When should I create new tags?

Most common tags already exist on a mature site. You should always favor existing tags; only create new tags when you feel you can make a strong case that your question does cover a new topic that nobody else has asked about before on this site.

But this doesn't seem to answer my question. It's unclear if a tag should only be created when there are no other tags that appropriately apply to the question, or if it's okay to do so whenever you personally feel that a topic isn't adequately covered by existing tag options.

For example, suppose you had a question about the Bekenstein bound. It would be appropriate to use tags like "black-holes", "black-hole-thermodynamics", "event-horizon", "gravity", and "general-relativity", but there is no existing tag for "Bekenstein-bound". Yes, that's within the realm of topics enveloped by those other tags, but none of them specifically address that concept.

Or alternatively, suppose you had a question about the complementarity paradox. Appropraite tags include things like "hawking-radiation", "entanglement", and possibly "black-hole-firewall", but there exist no tags for "complementarity-paradox", "fuzzballs", or "ER=EPR". So should such tags be created, or should you just rely on the existing ones since they are inherently connected topics?

I'm not trying to push any buttons or start any arguments. I'm just seeking further clarity on when this privilege should be used.

  • 3
    $\begingroup$ Try to see if there is at least a handful of question on the site where the newly created tag might apply. If there aren't after 10 years, it is probably too specific. (Conversely: If you repeatedly see questions which fall into the same "bin", it might be worth to create a tag.) $\endgroup$ Jun 7, 2023 at 20:51
  • $\begingroup$ Somewhere I have read an idea (possibly in an MSO comment): new tag is needed if you can imagine an expert of that topic, i.e. for example someone knowing very well that topic can be considered an expert. Possible analogue on the PSE: new tag X is a meaningful one if someone can say this: "I wrote my Phd/masters about X". It is just an idea, not an answer. $\endgroup$
    – peterh
    Jun 14, 2023 at 9:11

2 Answers 2


Well, if you have the privilege to create new tags, you can use it. The idea is that if other users find your tag useful, they'll start adding it to other questions, and if they don't, they won't. The existence of "bad" tags isn't directly harmful when they're only on a single question, and tags get automatically deleted when there aren't any questions tagged with them, so deleting a "bad" tag is as easy as removing it from the question again and waiting for a bit.

Generally, tags should be useful in grouping together sets of related questions, and there is a maximum of five tags per question, so we need to try to hit a sweet spot with the specificity of the tags - if the tag is so specific only very few questions could be tagged with it, should it take the place of another tag that would group the question together with more questions that are a bit more different but still of potential interest to people interested in the question?

To take an example, "ER=EPR" (aside from containing a '=' that doesn't work in tags) to me seems to be a full subset of "entanglement" + "general-relativity" - any question that could be tagged with "ER=EPR" could be tagged with "entanglement" and "general-relativity". At the same time, it's very specific to a single (though somewhat influential) conjecture. Are there really people who'd want to search for questions tagged with "ER=EPR" that wouldn't be fine with looking at questions tagged "entanglement" and "general-relativity" (or "wormholes") instead? Couldn't people interested specifically in "ER=EPR" just search for that term without use of a tag? I feel this way about most of your other proposed tags, too.

Anyway, within reason (so don't go off creating 100 new tags...), feel free to experiment with tags you think could be useful and see how others react to them, or, if you're not sure, ask here on meta whether others think a specific tag would be useful first.

  • $\begingroup$ Thank you. That's helpful. One question though. Suppose I create a new tag and that tag is later automatically culled after 6 months if nobody else uses it. Would the question I used that tag on lose the tag, or would it just stop being made available for new questions to use as a tag? $\endgroup$ Jun 7, 2023 at 20:28
  • 2
    $\begingroup$ @LoganJ.Fisher It would lose the tag. Since you hopefully used at least one previously existing tag to tag the question (like one of the large subfield tags like "quantum-mechanics" or "general-relativity"), that just means the question has one tag less. If by some weird accident a question loses all its tags, it ends up in untagged limbo $\endgroup$
    – ACuriousMind Mod
    Jun 7, 2023 at 20:32
  • $\begingroup$ And since there's nothing listed there, I'm guessing someone periodically checks there and adds tags to anything that ends up in untagged limbo? $\endgroup$ Jun 7, 2023 at 20:34
  • $\begingroup$ Well, I'm not checking it periodically, but I wouldn't be surprised if Qmechanic did :) $\endgroup$
    – ACuriousMind Mod
    Jun 7, 2023 at 20:38
  • $\begingroup$ I'd object to the usefulness of very specific tags. General tags like "entanglement" are mostly useful to have people subscribe to them, not so much to search questions (because so many questions will have them). Very specific tags are useful to subscribe to, for the (few) users interested in that specific topic, but also to quickly scan the site for questions about that topic. Sure, searching also works, but it can miss some posts (eg if a post uses a variation of the standard terminology). Specific tags create human-curated lists of posts about niche topics, which can be nice/handy $\endgroup$
    – glS
    Jun 9, 2023 at 18:10

Well, it may depend on the specific situation. Keep in mind:

  1. A tag is not really useful unless it is consistently applied. If tag X is only applied to a tiny fraction of all the posts belonging to topic X then searching for keyword X rather than tag X produces much more useful and complete results. So it is pointless to introduce a new tag X unless you're are willing to make an effort to apply it consistently (or at least for the leading posts) within topic X.

  2. Since a post can only carry 5 tags, too many different tags can fragmentize tag coverage.


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