I just tried to post a question with a Latin alpabet tags, and have been notified that tag is not allowed. Why it is not allowed?

a is not allowed

Despite of allowing any other single letter tag.

Seems this affects all of SE sites.

  • 1
    What happens if a isn't the first tag?
    – Oded
    Jul 12, 2017 at 12:05
  • @Oded it still complains about the a. The other letters seem to be fine. Apparently it's a globally blacklisted tag?
    – Floern
    Jul 12, 2017 at 12:12
  • @Oded I tried to add a in this post as 3rd tag and it still complains. Jul 12, 2017 at 12:34
  • 'a' is maybe a blocked tag, because it was created and burniated several times? A mod or a person with enough reputation should be able to check if that tag is blocked.
    – Tom
    Jul 12, 2017 at 12:52
  • 1
    Hypothesis: because it's frequently used as an indefinite article? As in "a thread". Type that into the tags field, you'll get [a] [thread].
    – D-side
    Jul 12, 2017 at 13:03

1 Answer 1


There are a few very common words that are not allowed as tags - and, or, the, a and a few others (this is configurable, so the list can change, which is why I am not listing all of them).

I believe this was done so edits would get rejected when a user simply writes a sentence in the tag input instead of actual tags.

  • Is this list site specific or global wide even for localized sites? Jul 12, 2017 at 13:12
  • It is global, though can be customised per site. I'd expect you would need to post a feature request on the per-site meta for changes to happen (and they would require a compelling reason).
    – Oded
    Jul 12, 2017 at 13:17
  • 1
    I need to create a programming language or technology with the name "a" at least! Jul 12, 2017 at 13:46
  • 2
    Given the average grammar skills on Stack Exchange, [i] needs to be blacklisted as well.
    – Glorfindel Mod
    Jul 12, 2017 at 14:59
  • 1
    @Glorfindel i would love to see the research on how English is used in the site
    – Ooker
    Jul 12, 2017 at 16:52
  • I could also see it being done to prevent an ambiguous [a] tag when asking a question about the HTML <a> tag.
    – Cole Tobin
    Jul 12, 2017 at 20:02

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