OneConfig is a modular, Compose-based configuration library for Minecraft mods, providing a unified API for config definitions, UI rendering, HUD management, keybind handling, event system, and notifications. It supports multiple Minecraft versions and mod loaders (Fabric, NeoForge) via a stonecutter-based build system and extensive mixin compatibility layers for third-party mod configs (e.g., YACL, ClothConfig, MoulConfig). The library features a custom Compose runtime (poly-compose) for Skia-accelerated UI, a tree-based config model with annotation-driven properties, and a service-loader-based platform abstraction. It is actively maintained with a large test suite covering config persistence, event validation, keybind codecs, and HUD migration.