NanoTorrentA tiny, hackable
BitTorrent client
NanoTorrent is a pure-Rust port of PicoTorrent — the same lean application, rebuilt without a single C++ dependency, now on Windows, macOS and Linux. One Slint window everywhere, dark mode, a built-in web remote, and it reads your existing PicoTorrent settings on first run.
Windows installer Microsoft Store macOS disk image Debian / Ubuntu .deb Fedora / RHEL .rpm Linux AppImage
One window, three platforms
The desktop client is drawn by Slint, so Windows, macOS and Linux get the same window rather than three approximations of it — and the web interface it ships with follows the same theme and the same language.
The torrents shown are Linux distribution images, used as sample data.
What’s new
0.4.1 is the polish on 0.4.0, which was the big one: streaming a file while it downloads, plugins that can start a program, and a file list that is finally a tree.
Host header, and a modern browser talking HTTP/2 does not send one — it sends :authority instead. So the check that keeps other sites out was keeping you out. It reads both now.
player.rhai. The list offered is the list found on your system, and one that cannot be located asks you where it is rather than failing silently.
execute is the eleventh permission and reads last in the approval prompt for a reason: it is reach over the machine rather than over your torrents. Every run and open is logged with the program and its arguments before the process starts, and nothing is shelled out, so a filename out of a torrent cannot become a second command. The shipped player.rhai is the proof — right-click a file, play it in your player — and it arrives switched off. The API is written up here ▸
set_location, add_torrent_file and stream_url — closing the gap against what an authenticated web client could already do. A plugin’s strings now live in a catalogue beside its script, so all three shipped examples carry no English at all and each ships translations for every one of the 76 languages.
Everything the original did — and then some
The full PicoTorrent feature set, ported across: settings database, translations, layout and all. Plus two things it never had — three platforms, and a web interface.
Windows, macOS and Linux
The front end was rebuilt on Slint, so it is one window and one codebase on all three. Ships as an .exe installer, a .dmg, .deb and .rpm packages, and an AppImage that needs no install at all — or install it from the Microsoft Store.
Built-in web interface
An Actix server over HTTPS — self-signed by default, Argon2id password hashing, a configurable per-address lockout that answers repeated failed logins with a 429, and it flatly refuses to listen off-loopback in plaintext. State arrives as a server-sent event stream rather than four polls a second, with an indicator that goes red and recovers on its own. It carries the desktop’s toolbar and speed charts, the same file trees with the same per-type icons, tabbed Details, multi-select, drag-and-drop adding, pagination with sorting that applies across every page, and a Preferences drawer holding every setting the desktop dialog has, in the configured language. The toolbar folds into the menu as the window narrows instead of wrapping onto more lines, and state names and background errors are translated rather than left in English.
Watch it before it finishes
The web interface serves byte ranges out of a file that is still downloading, so a Play button in the Files tab hands one file to whatever plays it. Seeking works on a partial download — the reader blocks on the piece under the read head and the engine goes and fetches it. The URL carries a capability token good for that one file for half an hour, never your password, and NanoTorrent launches nothing itself unless a plugin you approved does it for you.
Headless mode
Build with --no-default-features for no window at all — a seedbox daemon driven entirely through the web interface. And every preference the dialog offers is settable without one: --list-settings prints them all with their ranges, --get reads one, --set changes one.
Plugins, on a leash
Optional Rhai scripts react to session events and to a once-a-minute tick, and drive the session back through the web API’s own verbs. Eleven permissions — network for a capped http_get, data for a store of their own, ui for a window and a menu, and execute to start a program. Each is declared in a one-line header read before the script runs, and the plugin gets an engine holding only what it asked for, so reaching past the grant fails with “function not found”. A plugin can draw a form, put items on a file’s context menu, carry its own icon, and ship its own translations. Off by default; an RSS auto-downloader and a media-player launcher ship as working examples. Write one ▸
Share limits & scheduling
Stop seeding at a ratio, after a number of minutes, or whichever comes first — then pause or remove. Global, overridable per torrent, and off by default. Alternative speed limits run on a schedule, with a turtle in the toolbar for when you want them now.
Queue, priorities and tags
Top, up, down, bottom — from the toolbar or the context menu, with a multiple selection keeping its own order. Per-file priorities of skip, normal, high and maximum. And tags, many per torrent, where a label is one.
Watched & incomplete folders
Drop a .torrent into the watched folder and it is added, then renamed aside rather than deleted, so a misfire leaves the file where you can find it. Download into an incomplete folder and move to the save path when it finishes.
An encrypted settings file
The whole database, in pure Rust. The key lives in DPAPI on Windows and a 0600 file elsewhere — no password to type — and a change made outside NanoTorrent is detected rather than accepted. Settings, labels and filters export and import as JSON, with passwords and plugin permissions left out.
Live settings
DHT with a persisted routing table, UDP trackers, rate limits, SOCKS proxy with per-scope toggles, fast resume. Preferences ▸ OK rebuilds the session — no restart.
Strict network mode
Stop rather than leak. Turned on, it switches off whatever your VPN interface or SOCKS proxy cannot cover — DHT, uTP, local discovery, UPnP — refuses to start if the named interface is not there, and pauses every torrent if it vanishes while running. Interface binding works on Windows now too.
Live speed charts
Two of them in the toolbar, one per direction, each holding the last minute and riding the list’s own refresh tick rather than a timer of its own. Each scales to its own peak instead of a shared one, so upload is not flattened into a line along the bottom, and each states that peak in its tooltip. The web interface has the same pair.
The full torrent list
All 16 columns with a rendered progress bar, click-to-sort, multi-select, and the complete context menu: recheck, move storage, labels, tags, queue order, copy magnet, open in Explorer.
Details that matter
Overview with a piece-availability bar; a Files tree that folds, draws connectors and gives every row an icon from its type, with include toggles and priorities; peers with GeoIP country and flag; and trackers grouped into announce tiers — announced by tier, so a backup stays a backup — that you can add to, edit in place and remove, stored in the database and never written back into the .torrent. The whole list takes the keyboard.
Smart magnet adds
Magnet links fetch their metadata first, then show you the real file list in the same dialog you get for a .torrent — pick your files before it starts.
BitTorrent v2, not just the checkbox
v2-only .torrent files and v2-only magnets both download and seed, verified against their merkle piece hashes. No librqbit release implements BEP 52, so it is written here: the piece layers a magnet cannot carry are fetched with the v2 hash messages and checked against each file’s pieces root before a single byte of content is asked for. Incoming hash requests are now answered from those layers, so another client can bootstrap a v2 magnet from you. Hybrids announce under both info hashes at once.
The protocol, spelled out
Eighteen BEPs, fifteen in full: DHT, metadata exchange, the extension protocol, PeX, multitracker tiers, UDP trackers, the fast extension’s five messages, upload_only, padding files, compact peer lists and private torrents. MSE/PE encryption on connections both ways with require-encryption toggles, and anonymous mode to randomise the peer id. µTP (BEP 29) is there for where TCP is throttled — off by default, since it opens a second socket on the same port — and local service discovery (BEP 14) finds peers on your own network without a tracker, and is on. The README carries the whole table, checked against the vendored engine rather than the settings database.
Web seeds
A url-list seed (BEP 19) becomes a synthetic peer fed by HTTP range requests, so its pieces are hash-checked exactly like a real peer’s and a stale mirror is discarded rather than trusted. One request per piece rather than per 16 KiB chunk, and a failed fetch retries instead of killing the seed. httpseeds (BEP 17) rides the same shell, piece-oriented rather than file-oriented.
Torrent creation
Create BitTorrent v1, v2 or hybrid torrents (BEP 52) with trackers, comment and the private flag.
Native notifications
Windows 11 WinRT toasts on completion under a registered AppUserModelID, plus a tray icon that reports your transfer rates on hover. In-app toasts cover everything else on every platform — a failed add is red, not the same blue as “Copied to clipboard”.
Filters & labels
The PQL query subset — status = "downloading" and dl > 1kbps — with an optional console, plus coloured labels, save paths and auto-apply.
GeoIP & IP filtering
DB-IP country lookup for peers, and eMule / PeerGuardian blocklist support.
Bring your setup along
On Windows, first run copies your existing %LOCALAPPDATA%\PicoTorrent folder — settings and session state — leaving the original untouched. File ▸ Import from PicoTorrent then brings every torrent across in one shot, with its save path and its label.
Every translation
All 76 languages, complete — every string the UI can show, and a translated --help to go with it. Compiled into the executable, listed by their native names, and switchable live without a restart.
Lists that remember
An icon toolbar above the list, and columns you can drag, double-click to fit, or reset from a right-click. Widths are remembered per list — the torrent list and all three details tabs — along with the panel height and its divider.
Move storage & set location
Move relocates the files; Set location relocates the torrent, for data you moved by hand or restored from a backup. An intact copy verifies straight back to complete, and pointing it somewhere empty warns rather than quietly starting an 18 GB re-download.
Low-disk guard
Pause everything when free space on the save path drops below a percentage of the volume. librqbit has no such mechanism, so it is checked here every 30 seconds. Off by default; 5% when enabled.
One file, no baggage
Languages and 252 country flags are embedded at build time, and so is the web interface. The binary ships standalone — nothing needs to travel next to it.
Same job, three foundations
NanoTorrent against the client it is a port of, and against the one most people actually use. qBittorrent ships in two flavours — a libtorrent 1.2 build that speaks BitTorrent v1, and a libtorrent 2.0 build that adds v2 — so both are named wherever the answer differs between them.
| Aspect | PicoTorrent (C++) | qBittorrent (C++ / Qt) | NanoTorrent (Rust) |
|---|---|---|---|
| Platforms | Windows | Windows, macOS, Linux, FreeBSD | Windows, macOS, Linux — plus a headless build |
| BitTorrent engine | Rasterbar-libtorrent | libtorrent-rasterbar, shipped as both a 1.2 and a 2.0 build | librqbit 9.0.1, vendored and patched |
| BitTorrent v2 | — | Complete on the 2.0 build — v2-only torrents and btmh magnets included. The 1.2 build has none of it, and loads a hybrid as its v1 half | Every build, with no second download to pick. Hybrids announce in both swarms |
| GUI | wxWidgets (native Win32) | Qt | Slint — one window on all three, dark mode included |
| Remote control | — | WebUI and a Web API, polled on an interval | Actix over HTTPS with the desktop’s toolbar, charts and file trees, pushed as a server-sent event stream |
| Extensibility | — | Python search plugins | Rhai plugins with eleven declared, enforced permissions — network, storage, a window of their own, and starting a program |
| Leak protection | — | Interface binding and a proxy, honoured wherever the engine can | Strict network mode — refuses to start if the interface is missing, and pauses everything if it disappears |
| Settings storage | SQLite (PicoTorrent.sqlite) | .conf files, plus a .fastresume per torrent | The same SQLite schema, optionally encrypted, and exportable as JSON |
| Translations | lang/*.json embedded in a DB | Around 70, community-translated | 76, complete, compiled into the exe and switchable live |
| Command line | Torrent and magnet arguments | qbittorrent-nox, driven by the Web API | Every preference settable — and --help in all 76 languages |
| Notifications | Tray balloons | Native, per platform | Native on all three, plus in-app toasts |
| Packaging | NSIS installer | Installer, .dmg, distro packages, Flatpak | .exe · .dmg · .deb · .rpm · AppImage · Microsoft Store |
| Streaming while downloading | — | — | Byte ranges out of an unfinished file, seekable, behind a per-file token |
| Build requirements | MSVC and a C++ dependency tree | Qt, Boost and libtorrent | Rust 1.85+ · cargo build --release, and byte-for-byte reproducible |
Built on PicoTorrent
NanoTorrent is a port, not a rewrite from scratch. It owes its application structure, its settings database schema, its dialogs and its whole design philosophy to PicoTorrent — the excellent, deliberately small Windows BitTorrent client by Viktor Elofsson and contributors.
PicoTorrent is still available and still worth your time. If you're happy with it, keep using it — NanoTorrent exists for people who want the same experience on a memory-safe, C++-free stack.
This port is built predominantly with AI assistance under human review — see the AI declaration.
Visit PicoTorrentlibtorrent
librqbit
Where the edges still are
Most of what used to be listed here is done. This is what is left, and what changes when it runs packaged from the Store.
.torrent now serves its piece layers, so someone else can bootstrap a v2 magnet from it, and the handshake bit goes on for exactly those torrents. One root cause remains: the engine’s v2 seams are all add-time options, and session persistence does not carry them — so a restored torrent serves nothing until it is re-added from its file. Leaf-layer hash requests are also refused rather than computed, and a v2-only magnet’s layers are held by the resolver rather than installed. None of this has crossed a live swarm yet: the wire format matches libtorrent byte for byte and the merkle arithmetic is checked both directions, but the test swarm has gone dark.
url-list seed is served as a synthetic peer, so its pieces are hash-checked and a wrong one is discarded the way a bad peer is — but a server that ignores Range and answers 200 with the whole file is refused rather than downloaded. BEP 17 httpseeds is spoken now; FTP is not, and no client speaks it either.
execute starts its program on the machine running NanoTorrent, not the one holding the browser. That is the same trust as installing the plugin there, and the web interface is authenticated, but it is worth knowing before granting execute on a box you log into remotely.
execute starts a program; it does not open one. A plugin has data_* for its own state and stream_url for handing one file to a player — the bytes go from the session to the player without passing through the script. It also cannot read or change application settings, or create a torrent, since hashing a path is an indirect read of the file system.
lang/ folder next to the executable overrides a locale without a rebuild.
Give it a spin
Windows, macOS or Linux — an installer or a package each, plus an AppImage that needs neither and a Microsoft Store listing that keeps itself up to date. Your PicoTorrent setup comes with you, and the Discord is there if you get stuck.