Feather Manager

FeatherManager is a lightweight Paper plugin that detects and blocks Feather mods your server. It’s ideal for server owners who want to enforce a clean vanilla—or whitelisted mod—experience and prevent modified launchers from bypassing rules or introducing instability.

Key features:
Fast, low-overhead detection of Feather launcher at login.
Configurable block or warn behavior (kick, ban, or just log).
Customizable kick/warn messages and internationalization-friendly message keys.
Fine-grained whitelist and blacklist (by client brand string, plugin channel signatures, or handshake data).
Per-world and per-permission bypass support.
Admin commands for checking and manually banning/allowing players.
Minimal permissions footprint; integrates with common permission plugins.
Works on Paper (and compatible forks) — designed to be safe and efficient on production servers.

How it works:
FeatherManager inspects the client handshake and plugin message channels that are exchanged during login (client brand, custom payload markers, and other mod-identifying signals). When a match is found against your configured rules, the plugin applies the configured action (kick/ban/warn/log). Detection is configurable and extensible so you can add new identifiers as launchers evolve.

Example usage:
Automatically kick players using Feather mods.
Log join attempts from Feather Launcher for later review.
Allow specific players or groups (via permission) to join despite using Feather launcher.