Building Production-Grade LLM Evaluation Pipelines: From Vibes to Metrics

Building Production-Grade LLM Evaluation Pipelines: From Vibes to Metrics How we replaced "looks good to me" with automated evaluation catching 92% of hallucinations before deployment Three months ago, our team shipped a RAG-based customer support assistant. It worked great in testing — we'd ask it questions, read the answers, and say "yeah, that looks right." Then it hit production. A customer asked about their billing cycle. The assistant confidently cited a policy that didn't exist. Another asked about API rate limits and got numbers from a competitor's documentation. By the time we caught it, 500+ users had seen hallucinated responses. The post-mortem was brutal: we had zero automated evaluation. Our test process was literally "ask 5 questions, read answers, thumbs up." Academic benchmarks (MMLU, HellaSwag) don't tell you if your system works for your use case. Production evaluation needs: Domain-specific judges — Your criteria, not generic "helpfulness" Speed — Evaluation must run in CI/CD, not overnight Regression detection — Know immediately when a prompt change breaks things CI/CD integration — Block merges that degrade quality Golden dataset management — Versioned, stratified, growing test cases ┌─────────────┐ ┌──────────────┐ ┌────────────────────┐ ┌──────────────┐ │ Test Cases │────▶│ LLM Under │────▶│ Judge Ensemble │────▶│ Metrics & │ │ (Golden Set)│ │ Test │ │ - Faithfulness │ │ Regression │ └─────────────┘ └──────────────┘ │ - Instruction F. │ │ Detection │ │ - JSON Schema │ └──────┬───────┘ │ - Custom LLM │ ▼ └────────────────────┘ ┌──────────────┐ │ Dashboard/ │ │ PR Comments │ └──────────────┘ # eval/base.py @dataclass(frozen=True) class TestCase: id: str input: dict[str, Any] expected: dict[str, Any] | None = None tags: list[str] = field(default_factory=list) # ["edge-case", "long-context"] @dataclass(frozen=True) class EvaluationResult: test_case_id: str judge_name: str score: float passed: bool reasoning: str class Judge(ABC): @abstractmethod async def evaluate(self, test_case: TestCase, response: Any) -> EvaluationResult: ... class EvaluationHarness: def __init__(self, judges: list[Judge]): self.judges = judges async def evaluate_all(self, test_cases, generate_fn, concurrency=10): # Runs all cases through all judges with controlled concurrency ... RAGAS gives you faithfulness and answer relevance. But production needs more: Judge Purpose Type Threshold Faithfulness Answer contradicts retrieved context? LLM 0.8 Instruction Following All prompt constraints satisfied? LLM 0.9 JSON Schema Valid structured output? Deterministic 1.0 Safety PII, harmful content, policy violations LLM 1.0 Domain Expert Medical/legal/financial accuracy LLM (few-shot) 0.85 # eval/judges.py class LLMJudge(Judge): def __init__(self, name, criteria, model="gpt-4o-mini", few_shot_examples=None): self.name = name self.criteria = criteria self.model = model self.few_shot = few_shot_examples or [] async def evaluate(self, test_case, response): client = instructor.from_openai(AsyncOpenAI()) class Output(BaseModel): score: float = Field(ge=0, le=1) reasoning: str passed: bool result = await client.chat.completions.create( model=self.model, response_model=Output, messages=[ {"role": "system", "content": self._system_prompt()}, *self._few_shot_messages(), {"role": "user", "content": self._build_prompt(test_case, response)}, ], temperature=0.0, ) return EvaluationResult(...) def create_faithfulness_judge() -> LLMJudge: return LLMJudge( name="faithfulness", criteria=""" Evaluate whether the ANSWER is faithful to the CONTEXT. - Score 1.0: All claims in answer are directly supported by context - Score 0.5: Some claims unsupported but not contradictory - Score 0.0: Answer contains claims directly contradicted by context """, threshold=0.8, few_shot_examples=[ { "input": { "context": "Company founded in 2019. Revenue $10M in 2023.", "answer": "The company was founded in 2019 and reached $10M revenue in 2023." }, "output": {"score": 1.0, "reasoning": "All claims supported", "passed": True} }, { "input": { "context": "Product launched in January 2024.", "answer": "The product launched in March 2024 after extensive beta testing." }, "output": {"score": 0.0, "reasoning": "Contradicts launch date", "passed": False} }, ] ) Don't start with 1000 cases. Start with 50 real production cases. # eval/golden_set.jsonl {"id": "support-001", "input": {"question": "How do I reset my password?", "context": "..."}, "expected": {"answer": "Use the 'Forgot Password' link..."}, "tags": ["basic", "auth"]} {"id": "support-042", "input": {"question": "Why was I charged twice?", "context": "..."}, "expected": null, "tags": ["billing", "edge-case"]} Stratification matters: 40% basic/happy-path 30% edge cases (ambiguous, multi-step) 20% adversarial (injection, off-topic) 10% multilingual/long-context Version your dataset: Git-track it. Every production failure becomes a new test case. def regression_report(self, baseline: dict[str, float]) -> dict[str, Any]: current = self.summary() report = {} for judge_name, metrics in current.items(): if judge_name not in baseline: continue baseline_mean = baseline[judge_name] current_mean = metrics["mean_score"] diff = current_mean - baseline_mean # Statistical test (simplified - use proper stats in prod) report[judge_name] = { "baseline": baseline_mean, "current": current_mean, "delta": diff, "regressed": diff < -0.05, # 5% drop = regression "improved": diff > 0.02, } return report # .github/workflows/llm-eval.yml name: LLM Evaluation on: pull_request: paths: ['prompts/**', 'eval/**'] schedule: ['0 2 * * *'] # Nightly jobs: evaluate: runs-on: ubuntu-latest steps: - uses: actions/checkout@v4 - uses: actions/setup-python@v5 with: {python-version: '3.11'} - name: Install deps run: pip install -e .[dev] - name: Run evaluation env: OPENAI_API_KEY: ${{ secrets.OPENAI_API_KEY }} run: | python -m eval.run_suite --config config.yaml --output results.json - name: Check regressions run: | python -m eval.check_regression --baseline baseline.json --current results.json - name: Comment PR if: github.event_name == 'pull_request' uses: actions/github-script@v7 with: script: | const results = JSON.parse(fs.readFileSync('results.json')); const body = `## LLM Evaluation Results | Judge | Pass Rate | Mean Score | |-------|-----------|------------| ${Object.entries(results.summary).map(([k,v]) => `| ${k} | ${(v.pass_rate*100).toFixed(1)}% | ${v.mean_score.toFixed(3)} |`).join('\n')} `; github.rest.issues.createComment({ issue_number: context.issue.number, owner: context.repo.owner, repo: context.repo.repo, body }); Metric Before After Change Hallucination catch rate ~67% (human) 92% (auto) +25% Prompt iteration cycle 2 hours 15 minutes 8x faster Production incidents 3/month 0.2/month 15x reduction Regression detection Manual (days) Automated (minutes) — All MIT licensed, production-hardened: llm-eval-harness — Core framework (this article's code) prompt-registry — Git-based prompt versioning with eval history eval-dashboard — Real-time monitoring with alerting pip install llm-eval-harness from eval.harness import EvaluationHarness from eval.judges import create_faithfulness_judge, create_instruction_following_judge from eval.base import TestCase # 1. Define 10 real test cases from your logs cases = [ TestCase(id="1", input={"question": "..."}, expected={"answer": "..."}, tags=["basic"]), # ... ] # 2. Build judge ensemble judges = [ create_faithfulness_judge(), create_instruction_following_judge(), # Add your domain-specific judges ] # 3. Run harness = EvaluationHarness(judges) results = await harness.evaluate_all(cases, your_llm_function) print(harness.summary()) # 4. Save baseline harness.save_baseline("baseline.json") # 5. Add to CI — done Evaluation is infrastructure, not afterthought. Treat judges as first-class code (versioned, tested, reviewed) Golden dataset = your most valuable IP (curate it religiously) Every prompt change = eval run (enforced by CI) Regression alerts = paging alerts (not email digests) Your users don't care about your prompt engineering cleverness. They care that the answer is right. Automated evaluation is how you guarantee that at scale. Code: github.com/yourname/llm-eval-harness | Hacker News | @yourname