A new tag [c#-3.0] was recently created and added to 655745. I tried to retag it [c#3.0] to match the other 1167 questions, but nothing happens. Either using the quick retagging interface or by actually editing the post, the edit submits, there are no errors, but the tag remains unchanged.

I can change other tags, including removing a - from [entity-framework], so I initially thought it was something special about that particular tag. However, another new tag was created today that happens to fit the same pattern: [java-fx] on 1814332 should be [javafx], and again I'm unable to remove the -.

I have no idea why I can't retag those two but yet changing entity-framework to entityframework worked fine. I tried it in Firefox and Chromium and got the same behavior. Is it just me?

2 Answers 2


Pretty sure that's synonym remapping.


  • Oh, fantastic! I didn't know this was implemented Jul 19, 2010 at 5:46
  • So if c#3.0 is being remapped to c#-3.0, why aren't the 1167 instances of c#3.0 changing? Is it not retroactive? Jul 19, 2010 at 5:47
  • remapping != renaming Jul 19, 2010 at 5:48
  • I'm not sure what the difference is, and it seems odd that the source tags can stick around even though new ones can't be created, but I should probably go read the last week's worth of discussion about it that I somehow completely missed before I say anything Jul 19, 2010 at 5:51

As Jeff said, synonyms are in place now you can see them at: https://stackoverflow.com/tags/synonyms

I plan to improve the UI so it shows places where a merge probably makes sense (eg. a synonym is in place but old source tags still exist in the system)

Synonyms take effect for all new instances, but do not work retroactively (since tag merge renames are a risky process which has no undo we left out automatic renaming)

We plan to improve the synonym UI quite a bit in the next few weeks.

  • Can that page be sorted by alpha?, it would group all synonyms together and make it a lot more useful I think. Jul 19, 2010 at 11:18

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