I built a research-mode toggle for my LINE bot that actually

GeminiAPI turned a three-line summary into a cited, sectioned brief you can actually trust. Below is the exact prompt I ship to the model, plus the wiring notes so you can drop it into your own webhook.

The prompt (copy-paste ready) #

You are a research analyst. The user provides a URL or topic.
1. Use Google Search Grounding to fetch 8–12 authoritative sources published within the last 18 months.
2. Synthesize a structured report with these sections:
   • Executive Summary (3 bullets)
   • Key Findings (numbered, each with inline citation like [1], [2])
   • Contrasting Viewpoints (if sources disagree)
   • Data Points & Metrics (table-friendly numbers with units)
   • Open Questions / Gaps
   • Source List (full title, publication, date, URL)
3. Tone: professional, neutral, no fluff.
4. Output language: match the user's input language.
5. If grounding returns <4 usable sources, reply: "Insufficient recent coverage — try a broader query."

Why this prompt works #

Explicit source count & recency — "8–12 sources, last 18 months" stops the model from hallucinating old blog posts. Section schema — numbering the sections forces consistent structure; the frontend can render each as a collapsible card. Inline citation contract — [1]

style tags map 1:1 to the Source List, so the LINE flex message can make them tap-to-open. Failure guardrail — the "insufficient coverage" line prevents confident-sounding nonsense when the topic is too niche.

Wiring it into the LINE webhook (Node sketch) #

// webhook handler (express)
app.post('/webhook', line.middleware(config), async (req, res) => {
  await Promise.all(req.body.events.map(handleEvent));
  res.sendStatus(200);
});

async function handleEvent(event) {
  if (event.type !== 'message' || event.message.type !== 'text') return;
  const text = event.message.text.trim();

  // user taps the "Research Report" quick-reply button → payload starts with "research:"
  if (text.startsWith('research:')) {
    const query = text.slice(9);
    const report = await callGeminiWithGrounding(query);
    await pushFlexReport(event.source.userId, report);
  }
}

callGeminiWithGrounding

hits generativelanguage.googleapis.com/v1beta/models/gemini-1.5-pro:generateContent

with tools: [{ googleSearchRetrieval: {} }]

and the prompt above in systemInstruction

. The response's groundingMetadata.groundingChunks

gives you the citation URLs — map those to the [n]

markers before you build the flex JSON.

Cost & latency reality check #

Tokens: ~2.2k input / 1.8k output per report (Gemini 1.5 Pro)** Latency**: 6–9 s end-to-end (grounding adds ~3 s)** Bill**: ~$0.018 per report at current pricing — cheap enough for a freemium bot tier

One gotcha #

Grounding sometimes returns paywalled PDFs. I filter groundingChunks

for web.uri

containing .pdf

and drop them unless the domain is arxiv.org

or pubmed.ncbi.nlm.nih.gov

. Keeps the "tap to open" experience honest.

Ship the prompt, wire the webhook, and your users get a citeable brief instead of a paragraph guess.

Next Built a Reasoning Ledger prompt that captures why decisions →

All Replies （4） #

@NovaGuruURL hallucinations persist — tried a post-retrieval validator against a known domain list?