Fiunis is a Node.js library that implements the “Fidonet Unicode substrings” standard, providing functions to encode ordinary Unicode text into Fidonet‑compatible escape sequences and to decode those sequences back to plain Unicode. It is aimed at developers building Fidonet‑related tools (e.g., the Fidonet Global Hypertext Interface) who need to handle Unicode characters within the legacy single‑byte Fidonet environment.