Build a voice agent (Node, no framework)

Build a minimal voice-agent loop with Node.js built-ins only. There is no framework, package, or npm install: just node:http and fetch. This starter uses browser speech recognition and a stub response function; replace both with production components. Keep RIME_API_KEY on the server and call Rime over HTTPS. The Next.js, Vite, Express, and FastAPI starters show the same boundary in their respective frameworks.

Browser (mic + playback)  →  POST /api/tts (node:http)  →  POST https://coda.api.rime.ai/

Prerequisites

A Rime API key from the API Tokens page, exported as RIME_API_KEY
Node.js 20.11 or later. Nothing else is required.

1. Server

Create server.mjs:

server.mjs

import { createServer } from "node:http";
import { readFileSync } from "node:fs";
import path from "node:path";

const INDEX_HTML = readFileSync(path.join(import.meta.dirname, "index.html"));

async function handleTts(req, res) {
  let body = "";
  for await (const chunk of req) body += chunk;

  let text, speaker, modelId;
  try {
    ({ text, speaker = "astra", modelId = "coda" } = JSON.parse(body || "{}"));
  } catch {
    res.writeHead(400, { "Content-Type": "application/json" });
    return res.end(JSON.stringify({ error: "invalid JSON body" }));
  }
  if (!text) {
    res.writeHead(400, { "Content-Type": "application/json" });
    return res.end(JSON.stringify({ error: "text is required" }));
  }

  const host = modelId === "mistv3" ? "mist" : "coda"; // Each model has its own host.
  const rimeRes = await fetch(`https://${host}.api.rime.ai/`, {
    method: "POST",
    headers: {
      Authorization: `Bearer ${process.env.RIME_API_KEY}`,
      "Content-Type": "application/json",
      Accept: "audio/mpeg", // MP3; see the API reference for Opus, WAV, PCM, μ-law
    },
    body: JSON.stringify({ text, speaker }),
  });

  if (!rimeRes.ok) {
    res.writeHead(rimeRes.status, { "Content-Type": "application/json" });
    return res.end(
      JSON.stringify({ error: `Rime API error ${rimeRes.status}`, detail: await rimeRes.text() }),
    );
  }

  res.writeHead(200, { "Content-Type": "audio/mpeg" });
  res.end(Buffer.from(await rimeRes.arrayBuffer()));
}

createServer(async (req, res) => {
  if (req.method === "POST" && req.url === "/api/tts") return handleTts(req, res);
  if (req.method === "GET" && req.url === "/") {
    res.writeHead(200, { "Content-Type": "text/html" });
    return res.end(INDEX_HTML);
  }
  res.writeHead(404, { "Content-Type": "application/json" });
  res.end(JSON.stringify({ error: "not found" }));
}).listen(3000, () => console.log("Rime voice agent on http://localhost:3000"));

Verify it works before touching the frontend (create an empty index.html first if you’re testing the API route alone):

RIME_API_KEY=your_key node server.mjs &
curl -X POST http://localhost:3000/api/tts \
  -H 'Content-Type: application/json' \
  -d '{"text": "Hello from my plain Node voice agent."}' \
  --output test.mp3

test.mp3 should be playable audio. A 401 means RIME_API_KEY isn’t visible to the server process.

2. Client: mic in, Rime audio out

Create index.html next to server.mjs. It uses the browser’s built-in SpeechRecognition for input (Chrome/Edge/Safari), a stub respond() function as the agent brain, and your /api/tts route for the voice:

index.html

<!doctype html>
<html>
  <head>
    <meta charset="utf-8" />
    <title>Rime voice agent</title>
    <style>
      main { max-width: 480px; margin: 4rem auto; font-family: sans-serif; }
    </style>
  </head>
  <body>
    <main>
      <h1>Rime voice agent</h1>
      <button id="speak">🎤 Speak</button>
      <ul id="messages"></ul>
      <audio id="player" hidden></audio>
    </main>
    <script>
      // Replace this stub with a call to your LLM of choice.
      function respond(userText) {
        return `You said: ${userText}. This voice is Rime's Coda model.`;
      }

      async function speak(text) {
        const res = await fetch("/api/tts", {
          method: "POST",
          headers: { "Content-Type": "application/json" },
          body: JSON.stringify({ text }),
        });
        if (!res.ok) throw new Error(`TTS failed: ${res.status}`);
        const player = document.getElementById("player");
        player.src = URL.createObjectURL(await res.blob());
        await player.play();
      }

      function log(line) {
        const li = document.createElement("li");
        li.textContent = line;
        document.getElementById("messages").appendChild(li);
      }

      document.getElementById("speak").addEventListener("click", () => {
        const SR = window.SpeechRecognition ?? window.webkitSpeechRecognition;
        if (!SR) return alert("SpeechRecognition not supported in this browser.");
        const rec = new SR();
        rec.onresult = async (e) => {
          const userText = e.results[0][0].transcript;
          const reply = respond(userText);
          log(`You: ${userText}`);
          log(`Agent: ${reply}`);
          await speak(reply);
        };
        rec.start();
      });
    </script>
  </body>
</html>

Restart the server (it reads index.html at startup), open http://localhost:3000, select Speak, say something, and the agent answers in Rime’s astra voice.

Add streaming when latency matters

Legacy Coda /ws3. Use this section only for an existing /ws3 integration. For new clients, use the Coda WebSocket v1 JSON quickstart. Coda WebSocket v1 uses a different message format and does not return word timestamps.

For an existing /ws3 integration, connect your server to wss://users-ws.rime.ai/ws3 and relay events to the browser. Audio can then start while later sentences are still generating. Browser WebSockets cannot send the required Authorization header, so the bridge stays server-side. The browser-facing side adds one dependency, ws. The legacy Next.js bridge provides a complete bridge that works with the same createServer instance.

Production building blocks

WebSocket API overview

Compare Coda WebSocket v1 with the legacy endpoints, their message formats, and their synthesis controls.

Voices

Swap astra for any Coda voice. Coda covers ten languages, and each voice serves one of them.

Streaming formats

Choose between Opus, MP3, WAV, PCM, and μ-law for your latency budget.

TTS in five minutes

The core API walkthrough in cURL, Python, JavaScript, and TypeScript.

Get started

Build with Rime

Integrations

Account & updates

Build a voice agent (Node, no framework)

Prerequisites

1. Server

2. Client: mic in, Rime audio out

Add streaming when latency matters

Production building blocks

WebSocket API overview

Voices

Streaming formats

TTS in five minutes

​Prerequisites

​1. Server

​2. Client: mic in, Rime audio out

​Add streaming when latency matters

​Production building blocks

WebSocket API overview

Voices

Streaming formats

TTS in five minutes

Prerequisites

1. Server

2. Client: mic in, Rime audio out

Add streaming when latency matters

Production building blocks