diart is a Python library and CLI tool for real-time online speaker diarization, built on top of pyannote.audio. It processes audio streams (microphone, files, WebSocket) with low latency using a modular pipeline of segmentation, embedding, clustering, and aggregation blocks. The library is designed for both streaming and offline evaluation, with support for overlap-aware processing and hyperparameter tuning via Optuna. It provides a reactive streaming architecture using RxPY, making it suitable for building AI-powered audio applications. The repository includes a benchmark suite, expected outputs for standard diarization datasets (AMI, DIHARD, VoxConverse), and CI/CD pipelines. While primarily a software library, it has a strong research component with published results and reproducibility artifacts.