Sonarr, Radarr, Lidarr, Readarr and similar tools talk to download clients they already know. rDownloader answers as SABnzbd for Usenet and as qBittorrent for torrents, so it can be used as their download client without a plugin on either side. For front ends built for aria2 — AriaNg, Motrix-style front ends, browser extensions and Android remotes — it answers aria2's JSON-RPC as well.

No adapter can reach anything the native API does not already expose.

1. Create an API token under Settings → Clients & API → API & MCP with the areas api:intake, api:queue and api:read — what the adapters need, and nothing that reaches settings, stored credentials or administration. An api:* token works too. A read-only token does not work — these adapters add and delete. Every accepted key shows its last use in the token list and leaves a token_used entry in the audit log, like any other token.
2. Add a download client in your automation tool:
   • SABnzbd — host and port of rDownloader, no URL base (or sabnzbd if the tool insists on one), and the token as the API key.
   • qBittorrent — host and port, any username, and the token as the password.
   • aria2 — see The aria2 adapter; it has to be switched on first.
3. Create the category your tool uses — tv-sonarr, movies-radarr — under Settings → Storage & rules → Categories, with exactly that name.

Step 3 matters. The tool's own request to create its category is accepted without effect — categories are configured here, and routing rules decide the destination — so the category has to exist here for the tool to find what it queued.

The adapters can be used at the same time, from different tools, against one installation.

Served at /api and /sabnzbd/api, kept strictly apart from the native /api/v1. Authenticated with apikey= in the query or an X-Api-Key header.

Failures answer HTTP 200 with {"status": false, "error": …}, as SABnzbd does.

Mode	Status	Notes
version	Supported	Reports a SABnzbd version whose API this subset matches
auth	Supported	Always apikey
get_config	Supported	complete_dir and the category list only
get_cats	Supported	* plus the configured categories
fullstatus, status	Supported	Reachability probe
queue	Supported	Packages that have not reached an end state
queue&name=delete	Supported	Single id or value=all; cancels and cleans up part files
queue&name=pause, name=resume	Supported	Applies to every download of the package
pause, resume	Supported	Everything not finished
history	Supported	Completed and failed packages, with storage — also those that already left the queue, from the download history
history&name=delete	Supported	Comma-separated ids or all; the item leaves the tool's history, the native download history keeps it
addfile	Supported	Multipart NZB; queued immediately, not held for review
addurl	Refused	See Deliberate departures
addlocalfile	Refused	Answered like addurl; the message points at mode=addfile
del_files=1	Ignored	See Deliberate departures
Everything else	Reports failure	{"status": false, "error": "not implemented: …"}

Served at /api/v2, following qBittorrent's Web API v2. POST /api/v2/auth/login answers Ok. or Fails. and sets a SID cookie.

The cookie is a session value, not the API token, and a session ends with a restart, as in qBittorrent. An unauthenticated call answers 403, which clients read as "log in again".

Endpoint	Status	Notes
auth/login, auth/logout	Supported	Username ignored; password is the API token
app/version, app/webapiVersion	Supported
app/preferences	Supported	save_path, plus fixed values for the temp-path, subfolder, preallocation, queueing, DHT, PeX, LSD and listen-port fields
torrents/info	Supported	category and filter=completed|downloading narrowing; the category is reported and matched the way qBittorrent does it
torrents/properties	Supported
torrents/files	Supported	Resolved through the same evaluator as the interface
torrents/filePrio	Partial	Priority 0 deselects, anything else selects
torrents/add	Supported	.torrent upload and magnets; queued immediately
torrents/delete	Supported	deleteFiles=true does not delete finished files
torrents/pause, stop	Supported	A call that matched torrents but changed none reports failure; a partial one reports success and logs the rest
torrents/resume, start	Supported	Same
torrents/categories	Supported	The configured categories
torrents/createCategory, setCategory	Accepted, no effect	Categories are configured in rDownloader
torrents/setShareLimits	Supported	Mapped onto the per-torrent seeding override; -1 means "use the global setting", -2 means "no limit"
Everything else	404

Torrents are addressed by their BitTorrent info hash. A magnet whose metadata has not resolved yet is listed at once under the 40-character hex hash from its xt=urn:btih: parameter; a base32 or v2 btmh magnet is listed only once its metadata arrives.

It is off by default. Switch it on under Settings → Clients & API → API & MCP, card aria2-compatible clients, with Answer aria2 JSON-RPC; while it is off, the path /jsonrpc does not exist (404). The card shows the RPC address to copy (Copy RPC address).

Setting up AriaNg (or another aria2 front end):

1. Issue an API token with the areas api:intake, api:queue and api:read, as in Setting it up.
2. In AriaNg's AriaNg Settings → RPC, enter the RPC address http(s)://<host>:<port>/jsonrpc — host, port 8710 (or your reverse proxy's), path /jsonrpc — with the HTTP protocol and the POST method.
3. Paste the token as the secret token. A wrong, revoked or too narrow token is answered as aria2 answers a wrong secret (Unauthorized).

Method	Status	Notes
aria2.addUri	Supported	HTTP(S) and magnet links; only the first URI is taken, since aria2 reads the list as mirrors of one file. out names the file, pause adds it paused; dir is ignored — the category and routing rules decide where it goes
aria2.tellStatus	Supported
aria2.tellActive	Supported	Running, post-processing and seeding downloads
aria2.tellWaiting	Supported	Queued, waiting, blocked and paused
aria2.tellStopped	Supported	Completed, failed and cancelled
aria2.pause, forcePause, aria2.unpause	Supported
aria2.remove, forceRemove	Supported	The download leaves the list with its part data; a finished file stays
aria2.getGlobalStat, aria2.getVersion	Supported	The version reported is aria2 1.37.0
system.listMethods, system.multicall	Supported	listMethods needs the secret too
Everything else	Refused	No such method

Each download has a 16-digit GID, the form aria2 uses, which stays valid across restarts. Not available: the WebSocket transport and its notifications, addTorrent, addMetalink, the option methods (getOption, changeGlobalOption …), removeDownloadResult and purgeDownloadResult. Upload figures are always zero.

• addurl and non-magnet urls are refused. Fetching a URL chosen by the caller would let an API key reach whatever the service's machine can reach. Clients fall back to uploading the file, which all of them support.
• del_files=1 / deleteFiles=true do not delete finished files. Transfers are cancelled and part files cleared; deleting completed data stays a deliberate action inside the application.
• Categories are not created by a client; the call is acknowledged without effect.
• No adapter appears in the OpenAPI document.

Application	Usenet (SABnzbd)	Torrents (qBittorrent)
Sonarr	Contract-verified	Contract-verified
Radarr	Contract-verified	Contract-verified
Lidarr	Contract-verified	Contract-verified
Readarr	Contract-verified	Contract-verified
Prowlarr	Not applicable	Not applicable

"Contract-verified" is not "tested against that application." The test suite replays the call sequence these four issue — test connection, read configuration, add a release, poll for it, inspect it, remove it. It has not been run against real instances of them.

• Progress reporting is a snapshot. SABnzbd's timeleft and eta are 0:00:00 and unknown; qBittorrent's dlspeed is zero and its eta is 8640000 ("infinite"). Clients display these but do not act on them.
• Categories are matched by name. Both adapters report a job under the name of its category (* on the SABnzbd side for one without), and the qBittorrent adapter honours the category filter — so the category your tool uses has to exist here under exactly that name.
• Seed ratio and upload counters are zero on the qBittorrent side outside the seeding override. The native API is where torrent statistics live.

• REST API — the native API these sit beside
• Storage, categories and rules — creating the category
• Watched folders — the blackhole alternative
• Usenet and NZB · BitTorrent