# Example 01 — Basic Guarded Answer (No.1 Hallucination & Chunk Drift)
**Goal**
Stop the model from fabricating content. The model must answer only from provided evidence or return `not in context`.
This is the smallest change that gives a visible quality jump. Works with any LLM and any framework. No SDK lock-in.
**Problem Map link**
Targets **No.1 Hallucination and Chunk Drift**. Also improves traceability for No.2 and No.4.
**Outcome**
- Answers either cite real chunks or refuse politely
- You get a machine-readable trace for every question
- This takes 10–15 minutes on a laptop
---
## 1) Inputs
We use a tiny corpus so you can reproduce without extra tools.
Create `data/pages.json` and `data/chunks.json`.
```json
// data/pages.json
[
{"id":"p1","page":1,"text":"The library defines X. X is a constrained mapping. See also Y."},
{"id":"p2","page":2,"text":"Y is unrelated to X. It describes a separate protocol."}
]
````
```json
// data/chunks.json
[
{"id":"p1#1","page":1,"text":"X is a constrained mapping."},
{"id":"p2#1","page":2,"text":"Y is unrelated to X. It describes a separate protocol."}
]
```
---
## 2) Evidence-only template
Use the same template for Python or Node.
```text
Use only the evidence. If not provable, reply exactly: not in context.
Answer format:
- claim
- citations: [id,...]
```
---
## 3) Path A — Python (no external packages required)
Create `run.py`.
```python
# run.py -- minimal guarded answer with trace (no external deps)
import json, os, time, urllib.request
# 1) tiny in-memory "retriever" for the demo
def retrieve(question, chunks, k=2):
# naive keyword score to keep this example dependency-free
qs = set(question.lower().split())
scored = []
for c in chunks:
score = sum(1 for w in c["text"].lower().split() if w in qs)
scored.append((score, c))
scored.sort(key=lambda x: x[0], reverse=True)
return [c for _, c in scored[:k]]
# 2) prompt builder with the evidence-only template
def build_prompt(q, chunks):
ctx = "\n\n".join(f"[{c['id']}] {c['text']}" for c in chunks)
return (
"Use only the evidence. If not provable, reply exactly: not in context.\n"
"Answer format:\n"
"- claim\n- citations: [id,...]\n\n"
f"Question: {q}\n\nEvidence:\n{ctx}\n"
)
# 3) simple OpenAI call via HTTP (replace API key or swap to your LLM)
def call_openai(prompt, model=os.getenv("OPENAI_MODEL","gpt-4o-mini")):
api_key = os.getenv("OPENAI_API_KEY")
if not api_key:
raise RuntimeError("Set OPENAI_API_KEY first")
req = urllib.request.Request(
"https://api.openai.com/v1/chat/completions",
data=json.dumps({
"model": model,
"messages": [{"role":"user","content":prompt}],
"temperature": 0
}).encode("utf-8"),
headers={
"Content-Type": "application/json",
"Authorization": f"Bearer {api_key}"
}
)
with urllib.request.urlopen(req) as r:
j = json.loads(r.read().decode("utf-8"))
return j["choices"][0]["message"]["content"].strip()
# 4) guard + trace
def guarded_answer(q, all_chunks):
picks = retrieve(q, all_chunks, k=2)
prompt = build_prompt(q, picks)
txt = call_openai(prompt)
ok = "not in context" in txt.lower() or "citations" in txt.lower()
rec = {
"ts": int(time.time()),
"q": q,
"chunks": [{"id": c["id"]} for c in picks],
"answer": txt,
"ok": ok
}
os.makedirs("runs", exist_ok=True)
with open("runs/trace.jsonl","a",encoding="utf8") as f:
f.write(json.dumps(rec, ensure_ascii=False) + "\n")
return rec
if __name__ == "__main__":
chunks = json.load(open("data/chunks.json",encoding="utf8"))
# test A: should answer with citation [p1#1]
print(guarded_answer("What is X?", chunks))
# test B: should refuse
print(guarded_answer("What is Z?", chunks))
```
Run:
```bash
OPENAI_API_KEY=sk-xxx python run.py
```
Pass criteria:
* For “What is X?” the answer must contain “X is a constrained mapping.” and cite `[p1#1]`
* For “What is Z?” the answer must be exactly `not in context`
* Two lines appear in `runs/trace.jsonl`
---
## 4) Path B — Node (no SDK, single file)
Create `run.mjs`.
```js
// run.mjs -- minimal guarded answer with trace (no extra deps)
import fs from "node:fs";
import https from "node:https";
function retrieve(question, chunks, k = 2) {
const qs = new Set(question.toLowerCase().split(/\s+/));
return [...chunks]
.map(c => [c.text.toLowerCase().split(/\s+/).filter(w => qs.has(w)).length, c])
.sort((a,b)=>b[0]-a[0])
.slice(0,k)
.map(([_,c]) => c);
}
function buildPrompt(q, chunks) {
const ctx = chunks.map(c => `[${c.id}] ${c.text}`).join("\n\n");
return `Use only the evidence. If not provable, reply exactly: not in context.
Answer format:
- claim
- citations: [id,...]
Question: ${q}
Evidence:
${ctx}
`;
}
async function callOpenAI(prompt, model=process.env.OPENAI_MODEL || "gpt-4o-mini") {
const apiKey = process.env.OPENAI_API_KEY;
if (!apiKey) throw new Error("Set OPENAI_API_KEY first");
const body = JSON.stringify({
model,
messages: [{ role: "user", content: prompt }],
temperature: 0
});
const res = await new Promise((resolve, reject) => {
const req = https.request("https://api.openai.com/v1/chat/completions", {
method: "POST",
headers: {
"Content-Type": "application/json",
"Authorization": `Bearer ${apiKey}`,
"Content-Length": Buffer.byteLength(body)
}
}, r => {
let data=""; r.on("data", d => data += d);
r.on("end", () => resolve(JSON.parse(data)));
});
req.on("error", reject);
req.write(body); req.end();
});
return res.choices[0].message.content.trim();
}
async function guardedAnswer(q, allChunks) {
const picks = retrieve(q, allChunks, 2);
const prompt = buildPrompt(q, picks);
const txt = await callOpenAI(prompt);
const ok = txt.toLowerCase().includes("not in context") || txt.toLowerCase().includes("citations");
const rec = {
ts: Date.now(),
q, chunks: picks.map(c => ({id: c.id})),
answer: txt, ok
};
fs.mkdirSync("runs", { recursive: true });
fs.appendFileSync("runs/trace.jsonl", JSON.stringify(rec) + "\n");
return rec;
}
const chunks = JSON.parse(fs.readFileSync("data/chunks.json","utf8"));
console.log(await guardedAnswer("What is X?", chunks));
console.log(await guardedAnswer("What is Z?", chunks));
```
Run:
```bash
OPENAI_API_KEY=sk-xxx node run.mjs
```
Pass criteria are the same as Python.
---
## 5) Why this works
* The template blocks any text that is not derived from evidence
* The citations requirement forces explainability and makes debugging easy
* Refusal is a valid outcome when evidence is insufficient
* The trace file is a permanent breadcrumb. You can inspect drift by looking at query, chosen chunks, and the final answer
This removes a large class of hallucinations without any model-specific tricks. It also gives you a baseline that you can evaluate after every change.
---
## 6) Common mistakes and quick fixes
* **The model still fabricates**
Make sure your template appears at the very end of the system prompt and that nothing after it can override the rule. Keep temperature at 0 for tests.
* **Citations look wrong**
Ensure you pass chunk ids through the entire path. If your UI formats citations, keep the raw ids in the trace.
* **Refusal rate is too high**
You probably need better retrieval. Start with intersection of BM25 and embeddings then rerank, as in `getting-started.md`.
* **Trace file is empty**
Check write permissions and make sure you call the guard wrapper, not a direct model call elsewhere.
---
## 7) Next steps
* Move to **Example 03** to add intersection and rerank which usually improves citation hit rate
* Use the **Eval** examples to measure precision, refusal, and citation overlap on a small question set
* If you use Ollama or LangChain, keep this guard layer exactly as is. Call your LLM behind `call_openai` or replace it with your local client
---
### 🧭 Explore More
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|-----------------------|----------------------------------------------------------|----------|
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---
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