FluxDown

Downloads, Supercharged.

A blazing fast, multi-protocol download manager — the free & open-source IDM alternative.

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Highlights

• Dynamic download acceleration — Rust + Tokio engine with adaptive segmentation and slow-segment rescue

• Multi-protocol — HTTP/HTTPS, FTP, BitTorrent, eD2K, HLS & DASH streaming

• One engine, multiple clients — native GPUI desktop, Kotlin Android and SwiftUI iOS apps, React Web UI and CLI

• Browser integration — Chrome / Edge / Firefox extension with a 3-layer interception engine, plus a userscript

• AI-agent ready — built-in MCP (Model Context Protocol) server: let Claude, Cursor & other AI clients manage your downloads

• Automation & remote management — RSS subscriptions, scheduled queues, webhooks, plugins and optional FluxCloud device collaboration

• Local-first — free and open source, no ads, no account required for local downloads; resumable state stored locally by default

Related MCP server: unfetch

Features

Privacy: local downloads do not require a FluxCloud account. Cloud features are optional. Anonymous installation and daily-active statistics are controlled by analytics_enabled and can be disabled; they do not collect download/task information. This is not a zero-telemetry application.

FluxDown vs. IDM

Installation

Grab the latest build from GitHub Releases or fluxdown.com:

Browser Extension

Install the extension so FluxDown takes over browser downloads automatically:

The extension connects to the desktop agent through Native Messaging. A Tampermonkey userscript is also available.

NAS / Server

The current headless service is fluxdown-agent --server + fluxdownd, with an embedded Web UI. The Docker image retains the name ghcr.io/zerx-lab/fluxdown-server.

From a checkout, use the supplied Compose configuration:

docker compose -f docker/docker-compose.yml up -d

Open http://<server>:17800/ and set an access key in the first-run wizard. The key must contain 8–128 visible ASCII characters, including both a letter and a digit. Set it up on a trusted network before exposing the service; use an HTTPS reverse proxy for remote access.

• Server mode listens on [::]:17800 (IPv4 + IPv6, falling back to 0.0.0.0 without IPv6) by default; override it with FLUXDOWN_BIND.

• For unattended setup, supply FLUXDOWN_TOKEN through your deployment environment or secret manager, not a committed file. It initializes the key only if one has not already been set.

• Persist /data for the database, logs and access key, and /root/Downloads for downloads. The supplied Compose file uses a named data volume and docker/downloads/ on the host.

• Prefer SSD/cache storage for /data if download disks need to sleep.

• Native deployments must keep fluxdown-agent and fluxdownd in the same directory.

CLI & HTTP APIs

The fluxdown CLI connects to the running desktop or server HTTP API by default. On desktop, enable the management API in Settings → API Service first. Supply the access key via FLUXDOWN_TOKEN; use FLUXDOWN_URL or --url to select a remote server.

fluxdown ping
fluxdown add "https://example.com/file.zip"
fluxdown --json list

# Standalone mode: embed the engine instead of connecting to a service
fluxdown add --local "https://example.com/file.zip"

Standalone mode cannot share a data directory with a running engine: stop the service using that directory first.

Desktop defaults to 127.0.0.1:17800, with management API and MCP disabled until enabled. Server mode enables both by default and requires an access key. See the OpenAPI specification for the REST contract.

MCP Server (Model Context Protocol)

FluxDown ships a built-in MCP server so AI agents (Claude Desktop, Cursor, Cline, …) can manage downloads via the Model Context Protocol. It implements a stateless Streamable HTTP subset (JSON-RPC 2.0 over POST /mcp) on the same API port — no separate MCP process needed.

• Endpoint: http://127.0.0.1:17800/mcp for the default desktop configuration; use your server address for headless deployments

• Auth: Bearer token (Authorization: Bearer <token> or X-FluxDown-Token), shared with the management API

• Enable: Settings → API Service → toggle MCP endpoint (a token is generated automatically); the headless server enables it by default

Tools (12)

Client configuration

{
  "mcpServers": {
    "fluxdown": {
      "url": "http://127.0.0.1:17800/mcp",
      "headers": { "Authorization": "Bearer <your-token>" }
    }
  }
}

The MCP layer is implemented in native/api/src/mcp.rs on top of the same ApiHost trait that powers the REST management API and aria2-compatible JSON-RPC.

Architecture

One Rust download engine, multiple hosts and clients. Desktop uses fluxdown-desktop → fluxdown-agent → fluxdownd; headless deployments reuse the agent and daemon with a React Web UI. Native Android and iOS clients connect through UniFFI (native/mobile), using an embedded agent and daemon for local downloads or /rpc for remote hosts.

flowchart TD
    UI["GPUI desktop"] -->|"WebSocket /rpc"| AGENT["fluxdown-agent — UI gateway and desktop shell"]
    WEB["React Web UI"] -->|"WebSocket /rpc"| AGENT
    EXT["Browser Extension (WXT)"] -->|Native Messaging| NMH["fluxdown_nmh"]
    NMH --> AGENT
    CLI["fluxdown CLI"] -->|"HTTP API"| AGENT
    AGENT -->|"Authenticated JSON-RPC"| DAEMON["fluxdownd — download core"]
    DAEMON --> ENGINE["fluxdown_engine"]
    MOBILE["Native Android / iOS"] -->|"UniFFI"| CORE["fluxdown_mobile"]
    CORE -->|"embedded or remote"| AGENT
    LOCAL["fluxdown add --local"] --> ENGINE
    ENGINE --> PROTOCOLS["HTTP/HTTPS, FTP, BitTorrent, eD2K, HLS, DASH"]
    ENGINE --> DB[("SQLite / PostgreSQL")]

• Daemon owns downloads: engine, download database, queues, RSS, plugins and webhooks.

• Agent owns integration: UI gateway, FluxCloud account/sync, device collaboration, browser capture and desktop tray/lifecycle.

• Shared contracts: native/protocol defines transport-independent DTOs, methods and events; native/api exposes REST, aria2 and MCP through ApiHost, without depending on the engine.

• Engine independence: EventSink and HostSelection connect the engine to hosts. Only one engine may write to a data directory at a time; the diagram shows alternative hosts, not concurrent writers.

Building from Source

Start with the Rust toolchain and your platform's native build tools (MSVC on Windows, Xcode command-line tools on macOS). Linux desktop builds also need graphics, audio and tray development libraries; the maintained Ubuntu package list is in CI. Bun is needed for the Web UI. Android uses Android Studio's JBR, Android SDK/NDK and cargo-ndk; iOS uses Xcode.

# Clone the development branch (main = active development, stable = stable releases)
git clone -b main https://github.com/zerx-lab/FluxDown.git
cd FluxDown

Desktop (GPUI)

# Build desktop UI, agent, daemon and browser relay, then launch
cargo desktop-dev

# Build only (also stages a signed development .app on macOS)
cargo desktop-dev --build-only

The launcher reuses an existing desktop/service instance rather than forcibly restarting it. Quit the UI and stop its services before testing changes to running code.

Headless server & Web UI

# Build the Web UI BEFORE building the agent
cd web
bun install --frozen-lockfile
bun run build
cd ..

cargo build -p fluxdown_daemon
cargo run -p fluxdown_agent --features web-ui -- --server

The web-ui feature embeds web/dist into the agent binary at compile time. After changing the frontend, rebuild the Web UI and then the agent. FLUXDOWN_WEBROOT optionally serves a directory from disk instead.

For frontend development, run cd web && bun run dev in a second terminal while the server is running: Vite listens on port 5173 and proxies backend requests to port 17800.

CLI

cargo build -p fluxdown_cli
cargo run -p fluxdown_cli -- ping

Native mobile

Android lives in mobile/Android; iOS lives in mobile/FluxDown. Both use the shared Rust core in native/mobile and shared translations in assets/i18n.

# Android: use Android Studio's JBR as JAVA_HOME
(cd mobile/Android && ./gradlew :core:testDebugUnitTest :bridge:testDebugUnitTest :app:assembleDebug)
# iOS: from repository root
mobile/FluxDown/scripts/build-core.sh
(cd mobile/FluxDown && xcodebuild build -project FluxDown.xcodeproj -scheme FluxDown -destination 'generic/platform=iOS Simulator')

Official Android releases use the native project's ANDROID_NATIVE_* signing credentials. They cannot be installed over the old Flutter APK; back up needed data before uninstalling the old app. The retired Flutter SDK, Rinf and hub are no longer build prerequisites. Shared assets, legacy desktop data/theme upgrade compatibility and the website's legacy theme editor remain supported.

cargo test -p fluxdown_engine        # Engine tests
cargo test -p fluxdown_api           # HTTP / aria2 / MCP contracts
cargo test -p fluxdown_agent         # Gateway / server
cargo test -p fluxdown_cli           # CLI
cd web && bun test && cd ..          # Web UI
cargo test -p fluxdown_mobile        # Shared native mobile core

Contributing & Community

• Bug reports / feature requests — GitHub Issues or the website feedback page

• QQ Group — 832143651

Pull requests are welcome! Branch off main and target main — it is the development branch, while stable only tracks stable releases (maintainers advance it from main). Before submitting, please make sure:

cargo fmt --check
cargo clippy --workspace --all-targets -- -D warnings

See CONTRIBUTING.md for the full workflow.

License

Distributed under the GNU Affero General Public License v3.0.

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Made by zerx-lab