Pawlsa MCP

MCP server for Linux audio systems. Exposes ALSA hardware/MIDI state and PipeWire graph as MCP resources and tools over stdio.

Built to give AI assistants (Claude, etc.) direct read/write access to audio routing, mixer levels, and device enumeration on Linux.

What it does

Resources (read-only state):

• ALSA sound cards, PCM devices, mixer elements, device hints, MIDI sequencer ports
• PipeWire nodes, ports, and links with live state from registry listeners

Tools (mutations):

• pw_link_create / pw_link_destroy — route audio between PipeWire ports
• mixer_set_volume / mixer_set_switch — control ALSA mixer elements (volume, mute)
• play_wav — play a WAV file through ALSA (default device: pipewire)
• play_pcm — play base64-encoded raw PCM samples (s16le, s32le, f32le, f64le)

Requirements

• Linux with PipeWire and ALSA
• libasound2-dev / alsa-lib
• libpipewire-0.3-dev / pipewire
• Rust 2024 edition (1.85+)

Build

cargo build --release

Usage with Claude Code

Add to ~/.claude/claude_desktop_config.json (or your MCP config):

{
  "mcpServers": {
    "pawlsa": {
      "command": "/path/to/pawlsa-mcp"
    }
  }
}

Then use /mcp in Claude Code to connect. Resources are available via ReadMcpResourceTool and tools appear as mcp__pawlsa__*.

Usage with MCP Inspector

npx @modelcontextprotocol/inspector -- cargo run

Output format

Resources use a specialized columnar format that balances token use with visual clarity for users.

Mostly this is because we couldn't get json or other formats to readable in the claude code output. If the mime type ever gets respected this could switch to json.

id, state, media.class, node.name, node.description, ports(in/out) ▌ 29, suspended, N/A, Dummy-Driver, N/A, 0/0 ▌ 63, suspended, Audio/Sink, alsa_output.usb-..., PCM2902 Audio Codec Analog Stereo, 2/2

• , separates columns
• ▌ separates rows
• Both pass through JSON strings without escaping (unlike \n/\t)
• Header row names fields once, then data rows follow

Architecture

┌─────────────────────────┐         ┌──────────────────────────┐
│  Tokio Runtime          │  reads  │  PW Thread (std::thread) │
│                         │◄────────│                          │
│  PawlsaServer           │  Arc<   │  MainLoop + Context      │
│    ServerHandler impl   │  RwLock │  Core + Registry         │
│    read_resource()      │  <PwSt  │                          │
│    call_tool() ─────────┤► ate>>  │  Registry listener:      │
│                         │         │    global → bind proxy   │
│  ALSA calls inline      │  pw::   │    info → update state   │
│  (sync, fast)           │  chan   │    global_remove → rm    │
│                         │  nel    │                          │
│                         │────────►│  Command handler:        │
│                         │         │    CreateLink / Destroy  │
└─────────────────────────┘         └──────────────────────────┘

License

MIT