Subtitles are the one chore Sonarr and Radarr leave behind - Bazarr finishes the *arr media stack by automating them. It connects to both via their APIs and mirrors their libraries - it doesn't scan disk itself, it manages exactly what your *arr apps index. For every monitored episode and movie it checks existing internal and external subtitles against your language profiles, then hunts missing ones across dozens of providers - OpenSubtitles.com, Podnapisi, Addic7ed, Subscene, and many regional sources - covering 184 subtitle languages including forced/foreign-dialogue tracks. Matching is smarter than filename guessing: releases are compared by release group and source, some providers support exact file-hash matching, and every downloaded subtitle gets a percentage score. Set a minimum score per Sonarr/Radarr connection and Bazarr rejects weak matches; enable upgrades and it replaces previously downloaded subtitles when better ones surface. Out-of-sync files get fixed too - automatic subtitle synchronization realigns timing after download, triggered only below a configurable score threshold so good subs aren't touched. Per-show and per-movie language configuration, download history, manual on-demand search, and adaptive searching that throttles provider API calls round it out, all behind a clean Sonarr-style web UI written in Python. If your library serves multilingual viewers, this removes the last manual step.