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.
  • Andrew@piefed.socialEnglish
    0·
    1 day ago

    I don’t know. I’m still hung up about this ‘references’ thing, I think. It reads like you intend for your post to be an objective resource for others to use, but then fall back to it being good enough for your subjective purpose when questioned about it.

    It feels like wanting to have your cake and eat it - a authoritative-looking post that isn’t authoritative.