I just tried to add a tag for "implementation-defined-behavior" on SO but I couldn't because of the 25 char limit. I had to resort to an abbreviation (), which is rather ugly and to some extent thwarts the purpose of tags, i.e. easy indexing.

Although I acknowledge that too long tag names could be unwieldy, sometimes there are technical terms that cannot be abbreviated in any useful way (especially when there is no widespread acronym).

Could an increase of that limit be considered?


This is to respond to all the comments addressed at me that were triggered by the recent news brought up by @Shog9 in his answer.

Shog9 announced that the limit was raised to 35 chars network-wide, thus some people asked me to accept his answer instead of that of hildred's.


Sorry but, no, I won't accept Shog9's answer. Although I find the change very welcome, I think it is still somehow a sort of a patch for the SE network as it has evolved. A complex system such as SE network is now could well afford another mechanism vetted by high rep users/mods on per-site basis.

More explanation:

I really welcome the change, but this solution would have satisfied me at the time I originally posted my question. After all, 35 chars is probably a reasonable limit for a site like SO, or EE.SE where I'm currently active and committed.

At that time, IRRC, the SE network was still very young and there were very few sites on the network that rivaled SO in quality and traffic.

But time has changed since then, and there are sites that have greatly improved and that have the potential of outperforming SO in traffic (after all, there are more people watching TV or practicing mountain walking than programmers out there!).

Given how SE network has evolved, I still think that the right, long term, solution is option #5 in hildred's answer: in short, allow much longer names under the supervision of mods and as a new privilege for high rep users.

Abuse is always a possibility, even with shorter tag names or for other facilities of the sites. I don't see why, apart from some technical reason related to the structure of the system, hildred's solution (or kind of) could not be implemented with the same level of safety/security as other facilities.

There are sites, as it was shown by others, that desperately need a much higher tag length limit, if tags are to be useful for them.

As the name of something increases in length, meaningful abbreviations start to become unintuitive and not unique, hence you cannot expect people to gain any convenience when searching for an abbreviation they don't know about or that they must guess.

In the end, as on of those sites grows, the problem becomes ever worse, because funny abbreviations, with lots of still funnier synonyms, increase, rendering the tag system unreliable and inconvenient.

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    I'm sure that tag will be removed quickly, if not already. – animuson Sep 22 '13 at 21:50
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    @animuson is it for its length? I find it strange that we can have "unspecified-behaviour", "undefined-behavior" but not that one. – Lorenzo Donati -- Codidact.org Sep 22 '13 at 21:52
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    @LorenzoDonati - It's a meta tag. – nickb Sep 22 '13 at 21:54
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    @nickb Thanks for the pointer. I'm not totally convinced, yet. Although in general "unspecifed-behavior" could be seen as a meta-tag, in C and C++ "unspecified-behavior" (e.g.) is a strictly defined technical term, which pops-up continuously in threads: it is about the content of the posts. – Lorenzo Donati -- Codidact.org Sep 22 '13 at 21:59
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    @nickb: It’s not a meta-tag. “homework” is about the circumstances under which the question was asked. “implementation-defined-behavior” is about the question. – Ry- Sep 22 '13 at 22:00
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    Newest, highly significant, per-site development on the issue: literature.meta.stackexchange.com/a/761/50 – Christian Rau Jun 12 '17 at 20:23
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    Now that the limit has been lifted, the accepted answer should be changed to Shog9's announcement. – Stevoisiak Aug 9 '17 at 14:09
  • @StevenVascellaro although I welcome that announcement, I already explained that the original scope of my question has changed, as SE network developed. I still deem that on some sites a higher limit should be allowed. I still consider hildred's answer as the right thing to do (of course provided the thing could be implemented with reasonable effort). See also my comments to Shog9's announcement. – Lorenzo Donati -- Codidact.org Aug 9 '17 at 14:22
  • "of course provided the thing could be implemented with reasonable effort" given the amount of dev time available, and the fact that there hasn't been a single instance of abuse, no, this isn't worth pursuing – user160606 Aug 10 '17 at 9:21

I can see the value of longer tag names in some contexts as noted by Giles. So there are a number of courses of action possible:

  1. No change: simple, but does not really fix .
  2. Increase to 27 chars: fixes one specific problem, but both makes it more difficult for SO and does not help SFF if someone were to want to tag questions about John Joseph Adams book (44).
  3. Change this on a per site basis: This has the advantage of tuning it to the subject at hand so SO would be 25, CS at 30, and SFF at 50 (numbers subject to improvement by picking a source other than thin air). But this does not help with the the fact that in most cases long tag names can be improved and shortened.
  4. Make long tag names require high rep or a moderator to create or approve: those with create tag privilege can create tags up to 25 chars long, Anything else would be discussed on the site meta and placed by a high rep user or a placement attempt would go into a approval queue. This can be a new privilege or just lumped in with moderator tools.
  5. My favorite, combine options 3 and 4 so that the length limit on tags is site specific and can be bypassed by moderators and high rep users as needed on a case by case basis.
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    I think your suggestion makes much sense and should be implemented. I've accepted yours as the correct answer (see also my comment to the answer of Tim Post, which was the previously accepted answer). – Lorenzo Donati -- Codidact.org Apr 21 '17 at 10:23
  • @LorenzoDonati any chance you could accept Shog's answer? – user160606 Aug 9 '17 at 23:50
  • I still think that option 5 is still the way to go even with the recent increase to 35 chars. – hildred Aug 9 '17 at 23:58
  • @Hamlet see the edit to my question. – Lorenzo Donati -- Codidact.org Aug 10 '17 at 9:18
  • @hildred yes; see the edit to my question. – Lorenzo Donati -- Codidact.org Aug 10 '17 at 9:18

Thunderforge makes a compelling argument that the tag length limit should be longer than 25 characters.

Tim and animuson are quite right that shorter tags are generally better; regardless, supporting arbitrarily long tag names is out of the question for the foreseeable future - there are too many things that would break, that people would intentionally break. I guarantee you, the minute we were to allow 100-character tags some jackass would make a new programming language named bwaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaargh and CodeGolf would make it the topic of 80 new questions and everything would go to hell...

...But there are clearly quite a few legit, not-at-all-trolling uses for tags that run from 26 to 35 characters. And as luck would have it, the system tolerates 35-character tag-names as of a year or so ago.

So as of this afternoon, the maximum length of a tag name is 35 characters on all sites. Use those extra 10 characters wisely!

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    If i18n is good enough for internationalization, bw98rgh is good enough for bwaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaargh. – Adam Lear Aug 8 '17 at 22:19
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    Thank you to the Stack staffers involved in making this change! :) I've reached out on my regular stack's meta to see if there's anything we ought to rename now that we have an increased limit. – doppelgreener Aug 8 '17 at 22:58
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    Arqade already has a real life 'bwaa...argh' with mukashi-mukashi-aru-tokoro-ni-totetsumonaku-naka-no-warui-twintail-no-shimai-himesama-ga-irasshaimashita-to-sa (110 chars) – Robotnik Aug 8 '17 at 23:02
  • Awesome, Shog! I don't think I've seen a use for that long of a tag on Mechanics, but it's good all the way around. I know on other sites I frequent it will be a good thing (Movies, SciFi, Literature). Movie and book titles can be quite extensive. Good stuff! :o) – Pᴀᴜʟsᴛᴇʀ2 Aug 9 '17 at 0:09
  • Challenge Accepted? – Jamal Aug 9 '17 at 0:45
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    BTW, if you want to thank someone personally, @doppelgreener, Hamlet over on Literature and jmac conspired to badger us into revisiting this. The technical groundwork was laid back in '15 by Adam Lear and Nick Craver for the benefit of the Russian-language Stack Overflow. – Shog9 Aug 9 '17 at 2:44
  • Thanks for the good news! When I posted my original question I didn't envision the evolution of SE network and the increased need in tag lengths, but I strongly felt that any name other than "implementation-defined-behavior" was a brute hack and did completely thwart the need for such a tag. Since that time I switched my commitment to another SE site, namely EE.SE. I'm sure that those extra 10 chars will be useful there too. – Lorenzo Donati -- Codidact.org Aug 9 '17 at 7:54
  • Anyway, after reading the updates to this thread during the past years, I was convinced that in some contexts/sites a still longer limit should be allowed. I don't know how difficult could be to update the system to allow that, but it will be worth, IMO. Especially because the search functionality is still not great, and good tagging is paramount to search for a topic right now.... – Lorenzo Donati -- Codidact.org Aug 9 '17 at 8:00
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    ... As someone else already suggested, once the system were modified to be able to handle it, I don't see any severe security problem in having a, say, 50 or 100 char limit. A new privilege could be created for, say, 15k users who would be the only ones that could create 36+ char tag names. – Lorenzo Donati -- Codidact.org Aug 9 '17 at 8:00
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    For ruSO.main (not meta) it's still 30. Please make it 35 too. – αλεχολυτ Aug 9 '17 at 8:08
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    Aww, does this mean MathOverflow should rename the tag pseudo-differential-opera now that there is room for "-tors"? :( – Joonas Ilmavirta Aug 9 '17 at 9:29
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    Well, I can check "getting a Stack Exchange feature request implemented" off my bucket list. Thank you jmac, Adam, and Nick! – user160606 Aug 9 '17 at 18:43
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    There's a point of diminishing returns somewhere here, @Lorenzo... The proper long-term solution is probably the one we arrived at for the Documentation project: allow the creation of a "friendly name" for a tag that's rendered in select places when referring to the tag but not on questions' tag section nor actually typed when tagging things. – Shog9 Aug 9 '17 at 21:25
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    @Shog9 yeah, I think that would be nice. you're gonna have that for us tomorrow, right? ;-) – DForck42 Aug 9 '17 at 21:45
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    I'll, uh, add it to a list, @DForck42. – Shog9 Aug 9 '17 at 21:51

Further evidence that the 25 character limit is a problem on multiple sites

The current bounty for this question says:

The official staff answer is that there is one case where this is unnecessary, but it has been repeatedly pointed out that there are many cases where this is necessary.

To add evidence to there being many cases where this is necessary, below are actual meta posts about tagging things whose proper names exceed the 25 character limit and have no obvious short versions:

Anime & Manga

Board & Card Games




Portuguese Language

Role Playing Games

Science Fiction & Fantasy

Software Engineering

Stack Overflow

Unix & Linux

In pretty much all of these cases, an inferior equivalent with heavy abbreviations or missing letters had to be chosen in order to get around the hard-coded 25 character limit.

I shouldn't have to create a silly tag because PresentModalViewController or Teenage Mutant Ninja Turtles is too long. Please increase the tag character limit so that we can avoid these issues!

Anyone can feel free to edit this post if you know of more sites that have had meta issues brought up due to the 25 character tag limit

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    meanwhile on wales.stackexchange.com - llanfairpwllgwyngyllgogerychwyrndrobwllllantysiliogogogoch – marcellothearcane Jun 19 '17 at 20:43
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    @marcellothearcane Well, someone could try to make a tag for that place on Travel.SE. – Thunderforge Jun 19 '17 at 21:25
  • Just a few weeks ago Physics got done debating "nuclear magnetic resonance" at 26 characters. (We settled on "nmr" despite a general preference for writing tags out, BTW). And then we catch a break from Shog9. – dmckee --- ex-moderator kitten Aug 8 '17 at 23:18

While I'd support longer tags when moderator-approved, at the very minimum I'd like to see an error message when searching for a tag that is too long.

As an example, here's one that tripped me up for quite a while. If I search for on stackoverflow, I get results stating 0 questions tagged:

enter image description here

However, in reality there are 119 questions relating to DataContractJsonSerializer on stackoverflow - but they are tagged . It took me a while to realize that such a tag even existed, since the more natural is only one character too long.

Can the tag search results be modified to indicate that the tag being searched on is too long? Better yet, if there is a valid, known tag of 25 characters in length whose first 25 characters match the searched tag, can the results include a suggested redirection to the shorter tag?

(Update - Now that the limit has been lifted, I've introduced the tag on stackoverflow and have retagged the old questions.)

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    This answer still has good points, even with the raised limit. – called2voyage Aug 9 '17 at 11:54

It looks like the Stack Exchange staff may have had a change of heart.

The maximum tag length for Literature SE was increased to 32 characters on June 12, 2017.

This can be increased, but only up to a maximum of 35 characters.... [I] increased the allowed length to 32

In the comments, Shog9 explains that this is currently not a network-wide change, and that Literature SE is being used as a testing grounds for increased tag character limits.

It's not network-wide... [let's] try it here for a little bit & make sure nothing breaks unexpectedly. The only other place this has been changed from the default is the Russian-language Stack Overflow, and there are a lot of other differences there too - so this is the first time it's been changed on an otherwise-standard English-language site. Also, 32 is a nice round number.

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There is always a better way to tag something than using an atrociously long tag name and without using silly abbreviations which are even worse and extremely hard to find in the tag suggestions.

For your specific case, I would just drop one of the words. Possibilities:

Just make sure it gets a tag wiki and excerpt that clearly defines the tag's purpose.

If you're ever unsure about how a tag should be created due to the character limit, come to Meta and ask the community to help you. But increasing the character limit just isn't a good option.

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    I'd argue that the “implementation” is rather the important part — the standard defines lots of behavior that you can rely on from implementation to implementation, but it also leaves certain areas for implementations to define their own semantics, possibly making code non-portable between implementations. defined-behavior doesn't say whether the standard or implementations define it. You could say which in the tag wiki, but then you'd have to look at it to tell; it's not obvious at a glance like most other tags are. – icktoofay Sep 22 '13 at 22:31
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    I appreciate the advice, but I disagree on its applicability in this specific case. Just tagging as "defined-behaviour" could make more harm than good. There are atrocious discussions in C/C++ threads where something simply described as "defined behaviour" is the subject of heated debate. These technical terms (unspecified- impl.defined- and undefined-behavior) are of utmost importance in C/C++: failing to understand the implications may lead to erroneous programs with dire consequences (that's the C heritage). I don't think that an approximately named tag would satisify the C/C++ community. – Lorenzo Donati -- Codidact.org Sep 22 '13 at 22:43
  • @icktoofay If that part is important, then there's always implementation-behavior… or you could even drop the word "behavior" and make implementation-defined... – animuson Sep 22 '13 at 22:44
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    I think implementation-defined is probably the best abbreviation of this one. – Ry- Sep 22 '13 at 22:50
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    “defined-behavior” and “implementation-defined” have absolutely nothing to do with the intended meaning of the tag, they would be even worse than the abbreviated “implem.-defined-behavior”. The solution to “the name doesn't fit” isn't “pick an unrelated name that fits”. – Gilles 'SO- stop being evil' Sep 23 '13 at 9:12
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    What's a good tag name for implementation-defined-behavior (sorry, your three proposals are definitely silly abbreviations)? natural-language-processing? need-for-speed-most-wanted? windows-subsystem-for-linux? etc. – Gilles 'SO- stop being evil' Nov 14 '16 at 22:49

IMHO tags must be as short as possible, for readability, usage, and create exceptions to the rules can lead to abuse...

Concerning your specific case, I don't know what would be the best, but I really think @animuson suggests you valuable possibilities.


  • If the tag cannot be written in a concise manner, then it should probably be part of the title instead.

  • there are some sites that do not respect this rule? Ask to fix those sites instead of wanting increase the limit in the others.

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    I'd agree, but some folks at the C standard committee made a different choice, so we have to live with such mouthfuls as "undefined-behavior" and "implementation-defined-behavior". We cannot call them in another way, although "dragons" and "unicorns" would be shorter :-) – Lorenzo Donati -- Codidact.org Sep 22 '13 at 22:05
  • N.Frad,tsnba.Stjdfi25c. – Gilles 'SO- stop being evil' Nov 14 '16 at 22:33
  • @LorenzoDonati Easy solution: define a hash that spits out an 8-character hex value from any overlong tag name. BOOM. Problem solved. – hBy2Py Aug 9 '17 at 13:44
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    @hBy2Py Well, if we'd want to strive for compactness, why an hex hash? We could spit out a hash in Base64 encoding: even shorter! ;-) – Lorenzo Donati -- Codidact.org Aug 9 '17 at 14:03
  • @LorenzoDonati I bow to your obfuscational mastery, sir. :-) – hBy2Py Aug 9 '17 at 14:13

If you're wanting to exceed the maximum character limit for a new tag, experience has taught us that you probably want to re-think the tag and see if it can be broken out into more than one. Animuson suggested some good alternatives that could be used interchangeably and applied to a broader range.

Remember also that tags are candidates for inclusion in the title of the page when viewed, so the constraints are as practical as they are philosophical. Raising the limit here would be a little self-defeating in both aspects.

Others have noted that what you were trying to create is a meta tag and I don't think this is the case. The term oddly specific comes to mind, but that just points to the fact that the tag would be more useful if split into several.

And please, whatever you do, don't invent a programming language with a name that exceeds 25 characters or I'll have to eat this with salt & pepper.

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  • Thank you Tim. I think yours is the best answer to my doubts. I recognize, now that I understand the bigger picture, that asking for a higher limit was not really appropriate. I still think that the specific case is an oddball: oddly specific really captures the essence of the problem, so thank you for recognizing that. – Lorenzo Donati -- Codidact.org Sep 23 '13 at 18:27
  • BTW, many other people have provided useful insights (thanks, anyway!), but their answers weren't fully satisfactory, since they failed to recognize the fact that "implementation-defined" (or sth else) doesn't really hit the spot IMO (even if some come close). I wish there could be a way to ask the C/C++ SO community about that, since this issue is really specific to them. I fear that people not having enough experience in these languages maybe don't get the same "gut feeling" for what could be deemed just nitpicking. – Lorenzo Donati -- Codidact.org Sep 23 '13 at 18:31
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    “Don't invent a programming language with a name that exceeds 25 characters” — that's fine for SO, but how about caring about the rest of the network sometimes? I've hit this limit with diverse things like the name of software packages on Unix & Linux, the name of calculi on Computer Science, and the title of works on Science Fiction & Fantasy, all of which are the local equivalents of programming languages in terms of taxonomy and thus tag names. Therefore, please eat this status-declined with soy sauce, pickles and Spice. – Gilles 'SO- stop being evil' Jun 6 '15 at 19:17
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    Hell, not just calculi but whole domains. We have a natural-lang-processing tag on CS.SE, which is silly because nobody would search for “natural lang processing”: it's either “natural language processing” or “NLP”. On this specific example, maybe we should use nlp as the tag name… that's good for the people who know what it is, but then we get complaints from people who don't know the abbreviation. – Gilles 'SO- stop being evil' Jun 6 '15 at 19:23
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    And there are games with long names, that's a long-standing, well-motivated request. And Portuguese needs more letters than English. – Gilles 'SO- stop being evil' Jul 20 '15 at 12:55
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    After all this time has passed, it seems that the problem still remains, and since meta.SO has become meta.SE, the problem seems worse and seems to have a wider scope than I envisioned originally (when I was also a novice user of the network). Therefore I must retract the acceptance vote on your answer, sorry, since I think that the answer of hildred is better in this respect. Longer tag names should be allowed, I think. Abuse could be prevented by allowing them as a high-rep privilege and through community-moderation of borderline cases, as hildred suggested. – Lorenzo Donati -- Codidact.org Apr 21 '17 at 10:21
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    Unsurprisingly, this popped up on Literature as well. – Gilles 'SO- stop being evil' May 26 '17 at 19:39

The tag you want to create is Meta Tag. Tags should be used for technologies or libraries involved in questions. Such 'canonical' tags don't tend to be so extremely long, so the limit is actually doing what it is supposed to do.

Tags should be used for tags and not for descriptions. This is what Jeff's post is about.

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    In what way is it a meta tag? – doppelgreener Sep 23 '13 at 8:11
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    @JonathanHobbs it is about the symptoms or the implementation, not about the domain of the problem. What means 'implementation based'? Is it C, PHP, Java? But it's my interpretation of Jeff's post and the contept of meta-tags. Anyway, if you need to create such a long tag, something is wrong with it. – Danubian Sailor Sep 23 '13 at 8:16
  • I agree that something's wrong, but not that it's a meta tag. If you're asking about implementation-defined behaviour in C#, it's a perfectly suitable tag describing the content of the question, isn't it? – doppelgreener Sep 23 '13 at 8:26
  • I say that being fully open to the possibility it isn't - I have yet to wrap my head around what is and isn't a meta tag. – doppelgreener Sep 23 '13 at 8:40

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