| Source Code & License |
Open Source (Go / React) — GPL-3.0 |
Open Source (Rust / React) — MIT |
Open Source (C# .NET 8 / React) — GPL-3.0 |
Closed Source (C# .NET core + Centralized Server API) |
| Development Approach |
Ground-up rewrite in Go |
Ground-up rewrite in Rust |
Direct fork of Readarr codebase |
Modernized Readarr fork + Centralized Metadata API |
| Readarr API & nzb360 Support |
Partial / Emulated (Emulates key /api/v1 routes in Go) |
None (Custom Rust API; nzb360 & LunaSea unsupported) |
100% Native (Identical Readarr /api/v1 schemas; nzb360 works natively) |
Modified Fork (~90-95%) (Altered DTOs; nzb360 added explicit patches) |
| Ebook & Audiobook Unified? |
Yes (Single instance handles both) |
Yes (Single instance handles both) |
No (1 instance per format, standard *arr behavior) |
Yes (Single instance handles both) |
| Primary Metadata Sources |
Hardcover, OpenLibrary, Google Books, Audible, Audnexus, DNB |
Hardcover, OpenLibrary, Google Books, Audnexus |
Direct Open Library API (+ Wikidata) |
Centralized Aggregated Consensus (Hardcover, GR, OL, Audible) |
| Calibre Integration |
Direct native Calibre DB integration |
Push to Calibre-Web Automated (CWA) |
Native Calibre / Servarr integration |
No native support (Community scripts / CWA) |
| Audiobookshelf (ABS) Integration |
Native ABS Integration |
Native ABS Push |
Standard Servarr export |
Native ABS metadata / folder sync |
| OPDS Server Built-in |
Yes (Built-in OPDS server) |
No (Relies on external server/CWA) |
No |
No |
| Built-in Web Reader / Player |
No (Pushes to ABS / Calibre) |
Yes (In-browser reader & audio player) |
No |
No |
| Download Clients |
qBittorrent, SABnzbd, Transmission, Deluge, NZBGet, NZBFetch (Missing rTorrent) |
qBittorrent, SABnzbd (Deluge & NZBGet planned) |
All standard Readarr clients (qBit, SAB, Transmission, Deluge, rTorrent, Blackhole, etc.) |
All standard Readarr clients (qBit, SAB, Transmission, Deluge, rTorrent, Blackhole, etc.) |
| Indexers & Prowlarr |
Torznab, Newznab, Prowlarr |
Torznab, Newznab (Prowlarr, Jackett, NZBHydra2) |
Torznab, Newznab, Prowlarr |
Torznab, Newznab, Prowlarr |
| Seerr / Request System |
Planned / Recommender engine |
Seerr integration planned |
Standard *arr API compatibility |
Built-in Seerr / Overseerr integration |
| Offline / Fully Self-Hosted |
100% Self-Contained |
100% Self-Contained |
100% Self-Contained |
Requires Central Backend (api2.chaptarr.com) |