Add hello-snapshot UIWorker example
Smallest UIWorker demo: a voice LLM in the main pipeline delegates screen-relevant utterances to a UIWorker via a respond job; the UIWorker auto-injects the current <ui_state> and answers grounded in what's on screen. Includes a vanilla-JS client that streams accessibility snapshots over RTVI.
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Mark Backman
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examples/multi-worker/ui-worker/hello-snapshot/bot.py
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274
examples/multi-worker/ui-worker/hello-snapshot/bot.py
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#
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# Copyright (c) 2026, Daily
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#
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# SPDX-License-Identifier: BSD 2-Clause License
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#
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"""Hello UIWorker — the smallest possible accessibility-snapshot demo.
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A voice bot whose LLM delegates every screen-relevant utterance to a
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``UIWorker`` that sees the page and writes the spoken answer.
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Architecture::
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Main worker (PipelineWorker, owns transport + RTVI):
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transport.in → STT → user_agg → LLM → TTS → transport.out → assistant_agg
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└── answer_about_screen(query) tool
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└── params.pipeline_worker.job("hello", name="respond", payload={query})
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HelloWorker (UIWorker):
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└── @tool answer(text)
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The main LLM is the conversational layer: it forwards every utterance
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to the UI worker via the ``answer_about_screen`` tool and speaks the
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result. The UI worker's built-in ``respond`` job fires, which
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auto-injects the latest ``<ui_state>`` block into its LLM context. The
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UI worker's LLM picks the ``answer`` tool with a spoken reply grounded
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in what's on screen.
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The RTVI⇄bus UI bridge is built into ``PipelineWorker`` (active because
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``enable_rtvi=True``), so inbound ``ui-snapshot`` messages from the
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client are broadcast on the bus and the ``UIWorker`` stores them — no
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decorator or manual wiring needed.
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Why two LLMs for "hello world": this is the pattern UIWorker's
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auto-inject is built for. The UI worker auto-injects the current screen
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at the start of every delegated job, so the conversational LLM stays
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small and screen-unaware. Later examples (pointing, form-fill, deixis,
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async-tasks) compose new tools onto the same skeleton.
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Run::
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uv run python bot.py
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Then open the client at ``http://localhost:5173`` (see ``README.md``).
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Requirements:
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- OPENAI_API_KEY
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- DEEPGRAM_API_KEY
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- CARTESIA_API_KEY
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"""
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import os
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from dotenv import load_dotenv
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from loguru import logger
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from pipecat.adapters.schemas.tools_schema import ToolsSchema
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from pipecat.audio.vad.silero import SileroVADAnalyzer
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from pipecat.frames.frames import LLMRunFrame
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from pipecat.pipeline.job_context import JobError
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from pipecat.pipeline.pipeline import Pipeline
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from pipecat.pipeline.runner import PipelineRunner
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from pipecat.pipeline.worker import PipelineParams, PipelineWorker
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from pipecat.processors.aggregators.llm_context import LLMContext
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from pipecat.processors.aggregators.llm_response_universal import (
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LLMContextAggregatorPair,
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LLMUserAggregatorParams,
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)
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from pipecat.runner.types import RunnerArguments
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from pipecat.runner.utils import create_transport
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from pipecat.services.cartesia.tts import CartesiaTTSService
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from pipecat.services.deepgram.stt import DeepgramSTTService
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from pipecat.services.llm_service import FunctionCallParams
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from pipecat.services.openai.llm import OpenAILLMService
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from pipecat.transports.base_transport import BaseTransport, TransportParams
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from pipecat.transports.daily.transport import DailyParams
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from pipecat.workers.llm import tool
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from pipecat.workers.ui import UIWorker
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load_dotenv(override=True)
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MAIN_NAME = "main"
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transport_params = {
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"daily": lambda: DailyParams(
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audio_in_enabled=True,
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audio_out_enabled=True,
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),
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"webrtc": lambda: TransportParams(
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audio_in_enabled=True,
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audio_out_enabled=True,
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),
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}
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VOICE_PROMPT = """\
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You are the voice layer of a screen-aware assistant. A separate UI \
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layer sees the page the user is looking at and writes the spoken \
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reply for any question that could plausibly involve the page.
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## Routing rule
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For every user utterance that could involve the page in any way — \
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"what's on screen", "what does this say", "is X on the page", \
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factual questions, navigational questions, anything where the page \
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content might matter — call ``answer_about_screen`` with the user's \
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request verbatim. The tool's response is the spoken reply, already \
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TTS-ready; pass it through without paraphrasing.
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If the request has nothing to do with the page, still call the \
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tool — the UI layer falls back to general knowledge.
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## When to answer directly
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Only respond directly for pure pleasantries that don't need any \
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content awareness:
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- Greetings ("hi", "hello").
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- Acknowledgements ("thanks", "got it").
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- Goodbyes ("bye", "see you").
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Keep direct replies to one short spoken sentence. No markdown, no \
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lists, no symbols."""
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# The UI wire-format guide (UI_STATE_PROMPT_GUIDE) is appended to the LLM's
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# system instruction automatically by UIWorker, so this prompt only needs the
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# app-specific behavior.
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HELLO_PROMPT = """\
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You answer the user's question grounded in the page they're looking \
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at. The current ``<ui_state>`` block is in your context — use it for \
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anything the user could be asking about on screen.
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Always call exactly one tool: ``answer(text)``. Put the spoken reply \
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in ``text``. Plain language, one or two short sentences, no markdown \
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or symbols.
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When the question is about something on the page, ground claims in \
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the ``<ui_state>`` content. When it's general knowledge with no \
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on-page referent (history, geography, definitions), answer from your \
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own knowledge. Don't tell the user what you can't see — just answer \
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or admit you don't know."""
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class HelloWorker(UIWorker):
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"""Snapshot-aware layer. Answers grounded in ``<ui_state>``.
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``UIWorker`` defaults to ``active=True`` (unlike ``LLMWorker``)
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because the canonical UIWorker role is an always-on delegate, so it
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is online to receive snapshots and ``respond`` jobs as soon as its
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pipeline starts.
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"""
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def __init__(self):
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llm = OpenAILLMService(
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api_key=os.environ["OPENAI_API_KEY"],
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settings=OpenAILLMService.Settings(system_instruction=HELLO_PROMPT),
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)
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super().__init__("hello", llm=llm)
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@tool
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async def answer(self, params: FunctionCallParams, text: str):
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"""Speak ``text`` back to the user.
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Args:
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text: The spoken reply in plain language. One or two short
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sentences. No markdown, no symbols, no lists.
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"""
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logger.info(f"{self}: answer('{text[:80]}…')")
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await self.respond_to_job(speak=text)
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await params.result_callback(None)
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async def answer_about_screen(params: FunctionCallParams, query: str):
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"""Ask the screen-aware UI layer to answer about the current page.
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Args:
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query (str): The user's request, passed verbatim.
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"""
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logger.info(f"answer_about_screen('{query}')")
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try:
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async with params.pipeline_worker.job(
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"hello", name="respond", payload={"query": query}, timeout=30
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) as t:
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pass
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except JobError as e:
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logger.warning(f"hello job failed: {e}")
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await params.result_callback("Something went wrong on my side.")
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return
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speak = (t.response or {}).get("speak")
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await params.result_callback(speak or "I'm not sure how to answer that.")
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async def run_bot(transport: BaseTransport, runner_args: RunnerArguments):
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logger.info("Starting hello-snapshot bot")
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runner = PipelineRunner(handle_sigint=runner_args.handle_sigint)
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stt = DeepgramSTTService(api_key=os.environ["DEEPGRAM_API_KEY"])
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tts = CartesiaTTSService(
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api_key=os.environ["CARTESIA_API_KEY"],
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settings=CartesiaTTSService.Settings(
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voice=os.getenv("CARTESIA_VOICE_ID", "71a7ad14-091c-4e8e-a314-022ece01c121"),
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),
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)
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llm = OpenAILLMService(
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api_key=os.environ["OPENAI_API_KEY"],
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settings=OpenAILLMService.Settings(system_instruction=VOICE_PROMPT),
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)
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llm.register_direct_function(answer_about_screen, cancel_on_interruption=False, timeout_secs=60)
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context = LLMContext(tools=ToolsSchema(standard_tools=[answer_about_screen]))
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aggregators = LLMContextAggregatorPair(
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context,
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user_params=LLMUserAggregatorParams(vad_analyzer=SileroVADAnalyzer()),
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)
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pipeline = Pipeline(
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[
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transport.input(),
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stt,
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aggregators.user(),
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llm,
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tts,
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transport.output(),
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aggregators.assistant(),
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]
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)
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worker = PipelineWorker(
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pipeline,
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name=MAIN_NAME,
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params=PipelineParams(
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enable_metrics=True,
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enable_usage_metrics=True,
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),
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idle_timeout_secs=runner_args.pipeline_idle_timeout_secs,
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)
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@transport.event_handler("on_client_connected")
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async def on_client_connected(transport, client):
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logger.info("Client connected")
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context.add_message(
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{
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"role": "developer",
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"content": (
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"Greet the user briefly. Tell them they can ask about "
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"anything on this page. One short sentence."
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),
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}
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)
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await worker.queue_frame(LLMRunFrame())
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@transport.event_handler("on_client_disconnected")
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async def on_client_disconnected(transport, client):
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logger.info("Client disconnected")
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await runner.cancel()
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await runner.launch_worker(HelloWorker())
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await runner.launch_worker(worker)
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await runner.run()
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async def bot(runner_args: RunnerArguments):
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"""Main bot entry point compatible with Pipecat Cloud."""
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transport = await create_transport(runner_args, transport_params)
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await run_bot(transport, runner_args)
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if __name__ == "__main__":
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from pipecat.runner.run import main
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main()
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