Solution

The Lemmy server appears to have a database limit of 255 characters [2]; however, individual instances appear to put their own limits on username length though the frontend [3] and/or the API [4.1][4.2].

Original Post

If you know, please also provide relevant documentation.

UPDATE (2025-02-02T06:06Z): I did some brute-force testing, and, at least for sh.itjust.works, it seems that the maximum username length is 50, and the maximum password length is 60 [1].

References
  1. “Sign Up”. sh.itjust.works. Lemmy. Accessed: 2025-02-02T08:49Z. https://sh.itjust.works/signup.
    • When creating an account on sh.itjust.works, the sign-up form will throw this error if the provided password is greater than 60 characters in length.
  2. @TootSweet@lemmy.world To: [“[SOLVED] What is the maximum username length for a Lemmy account?”. “Kalcifer” @Kalcifer@sh.itjust.works. “Lemmy Support” !lemmy_support@lemmy.ml. sh.itjust.works. Lemmy. Published: 2025-02-03T00:54:51Z. https://sh.itjust.works/post/32085936.]. Published: 2025-02-02T05:57:26Z. Accessed: 2025-02-03T00:44Z. https://sh.itjust.works/post/32085936/16442382.

    It might be 255 characters? […]

    • They pointed to code on GitHub for the Lemmy server which outlines the length of the username data in the SQL database.
  3. “[SOLVED] What is the maximum username length for a Lemmy account?”. “Kalcifer” @Kalcifer@sh.itjust.works. “Lemmy Support” !lemmy_support@lemmy.ml. sh.itjust.works. Lemmy. Published: 2025-02-03T00:54:51Z. Accessed: 2025-02-03T00:46Z. https://sh.itjust.works/post/32085936.
    • §“Original Post”. ¶2.

      […] I did some brute-force testing, and, at least for sh.itjust.works, it seems that the maximum username length is 50 […]

      • The maximum username length for sh.itjust.works was found to be 50 characters by brute-force testing the length limit.
  4. “Andrew” @andrew_s@piefed.social To [“[SOLVED] What is the maximum username length for a Lemmy account?”. “Kalcifer” @Kalcifer@sh.itjust.works. “Lemmy Support” !lemmy_support@lemmy.ml. sh.itjust.works. Lemmy. Published: 2025-02-03T00:54:51Z. https://sh.itjust.works/post/32085936.] Published: 2025-02-02T19:57:49Z. Accessed: 2025-02-03T00:59Z. https://sh.itjust.works/post/32085936/16453656.

    1. curl -L http://lemmy.world/api/v3/site | jq -r .site_view.local_site.actor_name_max_length (26)

      • The maximum username length for Lemmy.world was found to be 26 characters via an API request.

    2. curl -L http://sh.itjust.works/api/v3/site | jq -r .site_view.local_site.actor_name_max_length (50)

      • The maximum username length for sh.itjust.works was found to be 50 characters via an API request.
  • Kalcifer@sh.itjust.worksOP
    0·
    1 day ago

    I think you can be an outsider to a particular system, and still be able to provide valuable information about it. […]

    I completely agree! It is also illogical to argue otherwise ­— sort of an appeal to authority, imo.

    For clarity, I wasn’t claiming that you were incorrect due to your self-professed insufficient level of expertise. I was simply responding to your argument that “it’s silly to ask you for advice because you don’t use Lemmy” by arguing that your premise is unjustified — your argument is valid; however, I don’t think that it’s sound. I interpret your logic as follows:

    1. (By your argument) If one is inexperienced with Lemmy, then it is unwise to ask their opinion.
    2. You claimed that you are inexperienced with Lemmy.
    3. Therefore, it is unwise to ask you for your opinion.

    This is a valid argument, as it follows by modus ponens; however, it is unsound, as the premise is not epistemologically justified, as I cannot know, pior to you telling me, what your experience is with Lemmy. Hence why I said:

    I don’t know you, so how would I know what your level of expertise is regarding Lemmy?

    • Andrew@piefed.socialEnglish
      0·
      1 day ago

      it’s silly to ask you for advice because you don’t use Lemmy

      That was never my argument. I think you know this.

      Being reluctant to answer any more questions about a topic doesn’t mean I was wrong to provide an initial answer. It just means my bandwidth has been exceeded. If Lemmy was a project I was invested in, and I didn’t think your second follow-up question was disingenuous, then it would’ve been different, but as things were, I resented being given homework about it.