Text Agent To Nova Sonic Voice

Migrate a Text Agent to a Nova Sonic Voice Agent

This skill converts any text-based agent into a real-time voice agent using Strands BidiAgent with Amazon Nova Sonic. The migration is broken into two layers:

1. Frontend — Browser client that captures mic audio and plays back voice responses over WebSocket
2. Orchestrator — FastAPI + BidiAgent server that takes the text agent's system prompt and tools and runs them as a bidirectional audio streaming agent

┌──────────────┐    ┌──────────────────────────────────────────┐
│   Frontend   │    │            Orchestrator                  │
│              │    │                                          │
│  Browser Mic  ─────▶ FastAPI /ws ──▶ BidiAgent ──▶ Nova Sonic│
│              │    │                     │                    │
│  Speaker ◀────────── WebSocket ◀── BidiAgent ◀── Nova Sonic  │
│              │    │                     │                    │
└──────────────┘    │              Tools (Strands @tool)       │
                    └──────────────────────────────────────────┘

Prerequisites — Extract from the Text Agent

Before starting, locate these in the existing text agent (any framework):

The extraction is framework-agnostic. Look for the system message and tool definitions in whatever orchestrator you're using — LangChain, CrewAI, AutoGen, raw OpenAI, Strands, Bedrock Converse, or custom code.

Part 1 — Frontend

The frontend is a browser-based WebSocket client that captures microphone audio, streams it to the orchestrator, and plays back audio responses. It also supports text input as a fallback.

WebSocket Connection and Config Event

On connect, the client sends a config event with the voice-optimized system prompt:

const ws = new WebSocket("ws://localhost:8080/ws");
ws.onopen = () => {
    ws.send(JSON.stringify({
        type: "config",
        voice: "matthew",                   // Nova Sonic voice
        model_id: "amazon.nova-2-sonic-v1:0",
        region: "us-east-1",
        input_sample_rate: 16000,           // Nova Sonic requires 16kHz
        output_sample_rate: 16000,
        system_prompt: voiceOptimizedPrompt  // migrated from text agent
    }));
};

Microphone Capture (AudioWorklet → base64 PCM)

const audioCtx = new AudioContext({ sampleRate: 16000 });
const stream = await navigator.mediaDevices.getUserMedia({ audio: true });
const source = audioCtx.createMediaStreamSource(stream);

await audioCtx.audioWorklet.addModule(processorUrl);
const worklet = new AudioWorkletNode(audioCtx, "pcm-processor");
source.connect(worklet);

worklet.port.onmessage = (e) => {
    ws.send(JSON.stringify({ type: "bidi_audio_input", audio: toBase64(e.data), format: "pcm", sample_rate: 16000, channels: 1 }));
};

The AudioWorklet converts float32 samples to int16 PCM. The main thread base64-encodes and sends over WebSocket.

Audio Playback and Event Handling

ws.onmessage = (event) => {
    const data = JSON.parse(event.data);
    switch (data.type) {
        case "bidi_audio_stream":  playAudioChunk(data.audio); break;   // base64 → PCM → speaker
        case "bidi_transcript_stream": displayTranscript(data.role, data.text); break;
        case "tool_use_stream":    showToolCall(data.current_tool_use.name); break;
        case "system":             showSystemMessage(data.message); break;
    }
};

Text Input Fallback

function sendText(text) {
    ws.send(JSON.stringify({ type: "text_input", text }));
}

Client Options

For the browser client, a Python HTTP server (client.py) serves the HTML:

python strands/client/client.py --ws-url ws://localhost:8080/ws

For detailed audio capture/playback implementation, see references/client-reference.md.

Part 2 — Orchestrator

The orchestrator is a FastAPI WebSocket server that wraps Strands BidiAgent with BidiNovaSonicModel. It receives the config event from the frontend, creates the agent with the voice-optimized prompt and tools, and runs the bidirectional audio loop.

Voice-Optimize the System Prompt

The text agent's system prompt must be rewritten for voice. Key transformations:

Add these to every voice prompt:

Use brief acknowledgments: "Sure thing!", "Let me check that for you."
If you don't understand: "I'm sorry, could you say that again?"
After helping: "Is there anything else I can help with?"
End warmly: "Thanks for calling, [name]. Have a great day!"

For a complete before/after example, see references/voice-prompt-guide.md.

Server (server.py)

The WebSocket server defaults to port 8080. Override via --port flag or PORT environment variable:

# Default (port 8080)
python server.py

# Custom port
python server.py --port 9000

# Or via environment variable
PORT=9000 python server.py

import logging, os, json, uvicorn
from fastapi import FastAPI, WebSocket
from fastapi.middleware.cors import CORSMiddleware
from agent import handle_websocket_session

app = FastAPI(title="Voice Agent Server")
app.add_middleware(CORSMiddleware, allow_origins=["*"], allow_credentials=True,
                   allow_methods=["*"], allow_headers=["*"])

@app.websocket("/ws")
async def ws_endpoint(websocket: WebSocket):
    await websocket.accept()
    await handle_websocket_session(websocket)

if __name__ == "__main__":
    import argparse
    parser = argparse.ArgumentParser()
    parser.add_argument("--port", type=int, default=int(os.getenv("PORT", "8080")))
    parser.add_argument("--host", default=os.getenv("HOST", "0.0.0.0"))
    args = parser.parse_args()
    uvicorn.run(app, host=args.host, port=args.port)

The client must connect to the same port: ws://localhost:8080/ws (or whichever port you chose).

Dependencies

System prerequisite (macOS):

brew install portaudio

System prerequisite (Debian/Ubuntu):

apt-get install -y portaudio19-dev gcc g++ make

Python packages:

pip install uvicorn fastapi websockets strands-agents strands-agents-tools aws_sdk_bedrock_runtime pyaudio boto3

aws_sdk_bedrock_runtime and pyaudio are not installed automatically by strands-agents — both must be installed explicitly:

• aws_sdk_bedrock_runtime — CRT-based bidirectional streaming client used by BidiNovaSonicModel
• pyaudio — imported at module level by strands.experimental.bidi.io.audio (requires portaudio system library)

Session Handler (agent.py)

from fastapi import WebSocket, WebSocketDisconnect
from strands.experimental.bidi.agent import BidiAgent
from strands.experimental.bidi.models.nova_sonic import BidiNovaSonicModel

async def handle_websocket_session(websocket: WebSocket):
    try:
        # 1. Receive config from frontend
        config = await websocket.receive_json()

        # 2. Voice-optimized system prompt (migrated from text agent)
        system_prompt = config.get("system_prompt", "You are a helpful voice assistant.")

        # 3. Create BidiAgent with Nova Sonic
        model = BidiNovaSonicModel(
            region=config.get("region", "us-east-1"),
            model_id="amazon.nova-2-sonic-v1:0",
            provider_config={
                "audio": {
                    "input_sample_rate": 16000,
                    "output_sample_rate": 16000,
                    "voice": config.get("voice", "matthew"),
                }
            },
        )
        agent = BidiAgent(model=model, tools=[], system_prompt=system_prompt)

        # 4. Input handler — routes text and audio from frontend
        async def handle_input():
            while True:
                message = await websocket.receive_json()
                if message.get("type") == "text_input":
                    await agent.send(message.get("text", ""))
                    continue
                return message  # audio frame

        # 5. Run bidirectional streaming
        await agent.run(inputs=[handle_input], outputs=[websocket.send_json])

    except WebSocketDisconnect:
        pass

Adding Tools to the Voice Agent

Tools from the text agent can be passed directly to BidiAgent using Strands @tool decorators. The tool logic stays the same — just pass them to the agent:

from strands import tool

@tool
def get_balance(account_id: str) -> str:
    """Get account balance for the given account ID.

    Args:
        account_id: The customer account identifier
    """
    # Same logic as your text agent's tool
    result = your_existing_function(account_id)
    return json.dumps(result)

# Pass tools to BidiAgent
agent = BidiAgent(
    model=model,
    tools=[get_balance],  # list of @tool-decorated functions
    system_prompt=system_prompt,
)

If you have many tools or want to use MCP servers, pass them via mcp_gateway_arn:

model = BidiNovaSonicModel(
    region="us-east-1",
    model_id="amazon.nova-2-sonic-v1:0",
    provider_config={"audio": {"input_sample_rate": 16000, "output_sample_rate": 16000, "voice": "matthew"}},
    mcp_gateway_arn=["arn:aws:bedrock-agentcore:us-east-1:123456:gateway/GW1"],
)

For the full orchestrator reference (large-event splitting, observability), see references/server-reference.md.

Project Structure

your-voice-agent/
├── server.py           # FastAPI WebSocket server (Part 2)
├── agent.py            # BidiAgent session handler + voice prompt (Part 2)
├── tools.py            # @tool-decorated functions (migrated from text agent)
├── client.py           # Python client that serves the HTML frontend
├── client.html         # Browser-based WebSocket client with mic/speaker
├── requirements.txt    # Python dependencies
└── README.md           # Setup and run instructions

Generated Client

Always generate a client alongside the server. The client is a simple Python HTTP server that serves an HTML page with WebSocket audio streaming.

client.py

#!/usr/bin/env python3
"""Serves the HTML client and connects to the voice agent WebSocket server."""

import argparse
import os
import webbrowser
from http.server import HTTPServer, BaseHTTPRequestHandler

class ClientHandler(BaseHTTPRequestHandler):
    ws_url = None

    def do_GET(self):
        html_path = os.path.join(os.path.dirname(__file__), "client.html")
        with open(html_path, "r") as f:
            content = f.read()
        if self.ws_url:
            content = content.replace("ws://localhost:8080/ws", self.ws_url)
        self.send_response(200)
        self.send_header("Content-type", "text/html")
        self.end_headers()
        self.wfile.write(content.encode())

    def log_message(self, format, *args):
        pass

def main():
    parser = argparse.ArgumentParser()
    parser.add_argument("--ws-url", default="ws://localhost:8080/ws",
                        help="WebSocket server URL (default: ws://localhost:8080/ws)")
    parser.add_argument("--port", type=int, default=8000,
                        help="HTTP server port for the client (default: 8000)")
    parser.add_argument("--no-browser", action="store_true")
    args = parser.parse_args()

    ClientHandler.ws_url = args.ws_url
    httpd = HTTPServer(("", args.port), ClientHandler)
    url = f"http://localhost:{args.port}"
    print(f"Client: {url}")
    print(f"WebSocket: {args.ws_url}")
    if not args.no_browser:
        webbrowser.open(url)
    httpd.serve_forever()

if __name__ == "__main__":
    main()

client.html

Generate a minimal HTML client with:

• WebSocket connection to the server
• Config event sent on connect (voice, model_id, region, sample rates, system_prompt)
• Microphone capture via AudioContext at 16kHz, converted to int16 PCM, base64-encoded, sent as { type: "bidi_audio_input", audio, format: "pcm", sample_rate: 16000, channels: 1 }
• Audio playback of received bidi_audio_stream base64 PCM chunks
• Text input fallback with a send button
• Transcript display for user and assistant messages

The HTML client should follow the patterns from Part 1 (Frontend). For a complete production-ready implementation, see strands/client/strands-client.html in this repo.

Generated README

When creating the voice agent, always generate a README.md with setup instructions including Python venv:

# [Agent Name] Voice Agent

Real-time voice agent using Strands BidiAgent with Amazon Nova Sonic.

## Setup

### System Dependencies

macOS:
\```bash
brew install portaudio
\```

Ubuntu/Debian:
\```bash
sudo apt-get install -y portaudio19-dev gcc g++ make
\```

### Python Environment

\```bash
python3 -m venv .venv
source .venv/bin/activate
pip install -r requirements.txt
\```

### Environment Variables

\```bash
# Set any required tool/service ARNs or API keys
export AWS_DEFAULT_REGION=us-east-1
\```

### Run

\```bash
source .venv/bin/activate
python server.py
\```

The WebSocket server starts on port 8080 by default. To use a different port:

\```bash
python server.py --port 9000
# or
PORT=9000 python server.py
\```

### Connect the Client

Open a second terminal:

\```bash
source .venv/bin/activate
python client.py --ws-url ws://localhost:8080/ws
\```

This opens a browser with mic/speaker controls. If you changed the server port, update the URL accordingly:

\```bash
python client.py --ws-url ws://localhost:9000/ws
\```

Examples

Three complete before/after migration examples in examples/:

• examples/langchain-migration/ — LangChain create_react_agent → BidiAgent + Nova Sonic
• examples/openai-migration/ — OpenAI function-calling → BidiAgent + Nova Sonic
• examples/custom-migration/ — Bedrock Converse → BidiAgent + Nova Sonic

Each contains text_agent.py (before), voice_agent.py (after), and a README.

Common Pitfalls

• Long system prompts: Keep the voice prompt under ~500 words. Move detailed tool instructions into tool descriptions.
• JSON in tool results: Nova Sonic will try to read JSON aloud. Return clean natural-language strings from tools.
• Sample rate: Nova Sonic requires 16kHz. A mismatch produces garbled audio with no error.
• WebSocket message size: Use split_large_event from strands/websocket/server.py for large audio payloads.
• Missing portaudio: The pyaudio package requires the portaudio system library. Install it before pip install.