Client tools

A client tool doesn’t call an API — the platform hands the call to your app over the websocket, your app runs the function, and returns the result. Use it when the “tool” is really a function in your frontend: update a cart, navigate a screen, or look up data that must not leave your side.

Configuration

A client tool has:

• Name / Description — the model reads the description to decide when to call it.
• Parameters — typed arguments the model fills from the conversation (name, type, description, required), same shape as an API tool’s LLM parameters.
• Wait for response — if on, the agent pauses until your app returns a result, and a timeout applies (1–60s, default 1s). If off, it’s fire-and-forget: your app acts on the event and the agent doesn’t wait.
• Filler phrases — spoken while the tool runs so the pause isn’t silent.

The protocol

Your app is the other end of the websocket and is responsible for executing the function. Two messages:

Agent → your app — the agent wants the tool run:

{
  "type": "function_call",
  "call_id": "<unique id>",
  "name": "<tool name>",
  "arguments": "<JSON-encoded string>"
}

Your app → agent — you return the result:

{
  "type": "function_call.result",
  "call_id": "<same id>",
  "output": "<JSON-encoded string>"
}

Rules:

• Echo the call_id back on the result so the agent can match it.
• Reply within the tool’s timeout. If you don’t, the agent stops waiting and recovers verbally.
• arguments and output are JSON strings — parse the arguments, and JSON-encode your result into output.
• If Wait for response is off, don’t reply — just act on the event.

Minimal handler

socket.onmessage = (event) => {
  const msg = JSON.parse(event.data);
  if (msg.type !== "function_call") return;
  const args = JSON.parse(msg.arguments);
  const output = handlers[msg.name](args); // your function, returns a value
  socket.send(JSON.stringify({
    type: "function_call.result",
    call_id: msg.call_id,
    output: JSON.stringify(output),
  }));
};

Open the websocket with a short-lived token (mint one, then connect to the agent websocket) and keep this handler running for the length of the session.

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