vocero-client/docs/client/tool-calling.md

Tool calling

The application supports native realtime function calling and server-side tool selection from model text. AquaPortal content uses authenticated MCP when S2S_MCP_URL is set; otherwise the legacy ApiPilot bridge remains available. A spoken promise to fetch something is not evidence that a tool executed.

Authenticated AquaPortal MCP

Vocero uses the official MCP Python SDK with Streamable HTTP. Each discovery or execution initializes a client with that conversation's opaque backend token as Authorization: Bearer .... JSON and SSE responses are supported. Neither browser values nor model arguments choose the authenticated user. There is no service-token override, anonymous retry, redirect following, or public REST fallback on this path. AquaPortal checks current permissions on every request, including its administrator and assigned report-manager access rules.

The backend phone login must return sessionToken plus user.id and user.name. The only allowed tool names are:

Tool	Content
list_reports	Accessible published reports with name, center, and date filters
get_report	One report or an explicit list of ambiguous selections
list_insights	Published findings, priorities, recommendations, and sources
get_metric_history	Dated metric values, units, centers, cages, and source reports
list_podcasts	Daily and report-associated episodes
get_podcast	Selected episode summary, highlights, and available media
read_podcast_transcript	Paginated transcript or report-script passages
get_my_briefing	Compact overview with actual source dates

Discovery preserves the complete input schema, including nested request, optional filters, references, and pagination. The executor validates arguments against that schema and supplies structuredContent to reasoning when present, falling back to MCP text content. It preserves get_report's result union and list next_offset values. Tool errors are data for the model to explain; expired authentication stops the conversation. Tool text is labeled as reference data, never as instructions or authorization.

Both reasoning paths can discover reports, retrieve details, and follow up with another tool before answering. The HTTP loop retains bounded completed-turn history. The realtime relay injects results into the speech service's existing conversation. Attempts are bounded per user turn (six by default), identical calls within a turn are rejected, and tool results are limited to 64,000 characters individually and 96,000 per turn. Each MCP operation has a timeout; HTTP reasoning also has a 180-second total timeout.

Selection uses an internal text marker, not a new speech protocol event:

<<<VOCERO_MCP_CALL:NAME=get_report,ARGUMENTS={"request":{"report_id":"example-id"}}>>>

The distinct marker is necessary because the current speech pipeline removes APIPILOT_CALL before emitting assistant text. The relay buffers undecided text/audio, handles transcripts emitted before response.created, executes the MCP selection, and requests another response. Normal speech continues using the existing PCM16 protocol. This leaves speech_to_speech/ unchanged, although the speech service may spend time synthesizing audio that the relay suppresses. Malformed selections fail with a user-facing error rather than permissive parsing.

New speech, cancellation, disconnect, and expiry invalidate pending work. Generation checks reject late results even if the transport does not stop in time. The browser receives vocero.tool.started / vocero.tool.failed status events, without backend credentials or raw tool arguments.

Automatic current-episode context from episode_id is not wired yet. The model must resolve a podcast with the catalog rather than fetching an unauthenticated episode URL. See usage for configuration, conversation endpoints, single-worker constraints, and the retained unsafe phone selector.

Native realtime function calls

The browser sends tool declarations inside the session object:

{
  "type": "session.update",
  "session": {
    "type": "realtime",
    "tools": [
      {
        "type": "function",
        "name": "web_search",
        "description": "Search the web for information.",
        "parameters": {
          "type": "object",
          "properties": {"query": {"type": "string"}},
          "required": ["query"]
        }
      }
    ],
    "tool_choice": "auto"
  }
}

Keep configuration inside session, not at the event root. The backend has a legacy flat-payload compatibility path, but new clients should use the nested shape. The current browser's activeToolDefs() declares web_search when enabled and a deploy/user search key is available. It does not load the old remote agent-profile MCP catalog into native session tools.

For a native call, the backend emits:

{
  "type": "response.function_call_arguments.done",
  "call_id": "call_example",
  "name": "web_search",
  "arguments": "{\"query\":\"example query\"}"
}

arguments is a JSON-encoded string. The WebSocket client validates the event and dispatches tool; controller.ts parses the arguments and runs the supported executor. Web search uses POST /api/search, keeping the deployment's Serper key on the server. Tool output returns to the model as:

{
  "type": "conversation.item.create",
  "item": {
    "type": "function_call_output",
    "call_id": "call_example",
    "output": "Tool result text"
  }
}

The client requests follow-up generation with response.create when the result should be spoken. A function_call_output item alone does not start generation. See the realtime API guide for local model <code> extraction and native remote-provider tool calls.

ApiPilot discovery and execution

When MCP is disabled, S2S_APIPILOT_TOOLS_URL enables the legacy dynamic-tool bridge. The backend discovers tools through its /tools route and executes through /execute. S2S_APIPILOT_TOOLS_EXECUTE_URL can override the execution target. The same-origin UI server exposes:

• GET /api/apipilot/tools?include_unauthorized=true: discovery envelope with data.tools, data.count, and data.include_unauthorized.
• POST /api/apipilot/execute: body {"name":"tool_name","arguments":{}} and a success/data/error envelope.

Tool definitions contain name, description, JSON Schema parameters, and requires_auth. Execution looks up the current discovery cache, refreshes once if the tool is missing, and applies an authorization gate and argument validation before forwarding. Caller Authorization and x-demo-session can be forwarded; configured service credentials and login-by-phone provide additional server paths. Display error.message to the user; keep error.code, error.status_code, and error.raw for diagnostics.

The discovery cache defaults to 300 seconds server-side (S2S_APIPILOT_TTL_SEC) and can be refreshed with refresh=true. The browser also keeps a per-user catalog cache. ApiPilot configuration is independent of S2S_INJECT_PROFILE.

Marker-based two-pass reasoning

The browser and proxy add an ApiPilot catalog as instruction text, including tool names, descriptions, authentication requirements and required parameters. The model is instructed to emit a call marker when it chooses a matching tool:

<<<APIPILOT_CALL:NAME=tool_name,ARGUMENTS={"parameter":"value"}>>>

Tool names are exact identifiers and must not be translated. The local realtime proxy accumulates assistant text, detects the marker, validates and executes the ApiPilot call, then injects the result as context and requests a new response. The HTTP reasoning route has analogous discovery/execution and second-answer handling. Internal marker text and its speculative audio are filtered from user output where those handlers run.

This marker is not response.function_call_arguments.done, and ApiPilot prompt discovery is not the same as declaring a native session.tools array. Direct browser connections bypass the local relay's marker executor even if the browser includes catalog instructions.

Retired documentation assumptions

The former HOWITWORKS.md described /api/mcp/tool, remote S2S_AGENT_PROFILE loading, and Spanish/Italian-to-English client ranking. Those APIs/rankers are absent from the current client/server path. The retained agent-profile JSON is an illustrative historical/example shape. Add or modify current ApiPilot tool definitions in the provider; do not restore obsolete endpoints solely to match older documentation.

Verify a tool turn

1. Confirm /api/config reports the intended feature and connection mode.
2. Inspect session.update: native tools and ApiPilot instruction text are separate evidence.
3. For native calls, find response.function_call_arguments.done, then the browser toolcall and executor request.
4. For ApiPilot, find the discovery, call-marker detection and execution logs.
5. Confirm the tool result reaches the model and follow-up text/audio reaches the browser. A spoken acknowledgement alone does not complete the flow.