Eval Design

Eval Design

Design high-quality evaluation datasets that measure what actually matters for your application. You extract evaluation dimensions from business context, structure them into stratified test cases, and output datasets ready for OpenJudge GradingRunner.

When to Activate

• User has agent traces / production logs and wants to build an eval set from them
• User has evaluation principles but needs properly stratified test data
• User wants to generate adversarial examples that stress-test their system
• User needs coverage analysis — are they testing all the right things?
• User wants a labeling guide for human annotators

Checklist

You MUST create a task for each item and complete them in order:

1. Extract eval dimensions — from traces, spec, or user interview
2. Design stratified sampling — 60/30/10 split with difficulty strata
3. Generate test data — synthetic inputs + adversarial examples
4. Output OpenJudge dataset — structured format ready for GradingRunner

Coverage check: run the bundled script

After you have a dataset, validate coverage with the bundled, tested script (scripts/coverage_check.py, standard library only, no OpenJudge dependency) before trusting any per-slice metric:

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python scripts/coverage_check.py --dataset eval-data/dataset.jsonl

It reports per-dimension and per-(dimension × stratum) counts, flags thin cells (< 5 per dimension, < 10 per cell), checks the adversarial share (≥ 10%), and returns a verdict (adequate / thin_coverage; exit 0 if adequate). --self-test to verify it.

Step 1: Extract Evaluation Dimensions

From traces (when user has production data)

Read the user's agent traces to identify what can go wrong:

1. Cluster failures: Group trace errors by type — tool call failures, hallucination patterns, off-topic responses, format violations, timeout/performance issues.
2. Map to dimensions: Each failure cluster becomes an evaluation dimension. Example: traces showing 15% of responses with wrong order numbers → order_accuracy dimension.
3. Prioritize by frequency: Sort by prevalence. Focus on what actually fails in production, not what might theoretically fail.

From spec (when user has product docs)

Read the spec / design doc and extract:

1. Hard constraints: Things the system must never do (e.g., "never expose PII", "never recommend competitor products"). These become conjunctive gate checks.
2. Quality expectations: What "good" looks like per scenario. Extract pass/fail boundaries from user stories and acceptance criteria.
3. Edge cases: What the spec explicitly calls out as tricky or boundary scenarios.

From interview (when user has neither)

Ask the user to describe (in one go, not question-by-question):

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Briefly describe:
- Who uses this system and what do they ask it to do?
- What are 3 examples of a perfect response?
- What are 3 examples of an unacceptable response?
- What failures keep you up at night?
- Are there any hard red lines the system must never cross?

Output: Test Plan

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# Write this into the user's project as eval-design.md frontmatter
scenario: "Customer support chatbot for e-commerce"
stakes: production
dimensions:
  - id: order_accuracy
    criterion: "Order number, status, and tracking info must match the backend"
    priority: P0
    source: trace_failure_cluster
  - id: tone_appropriateness
    criterion: "Response tone matches customer sentiment"
    priority: P1
    source: spec
  - id: no_hallucination
    criterion: "No fabricated policies, prices, or product features"
    priority: P0
    source: hard_red_line

Step 2: Design Stratified Sampling

A flat random sample hides systematic failures. Stratify by difficulty so your eval detects degradation where it matters most.

Difficulty Strata

Sample Size

Don't guess. Use this rule: for per-stratum TPR/TNR to be meaningful, each stratum needs at least 10 samples (binomial CI at n=10, p=0.5 → half-width ~±15%). For production use, target 30+ per stratum (CI narrows to ~±9%).

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# Minimum viable: 10 samples × 3 strata = 30 per dimension
# Production target: 30 samples × 3 strata = 90 per dimension

Data Design Quadrants

For each eval dimension, cover four types of cases (adapted from community practice):

Step 3: Generate Test Data

Synthetic data generation

Use 3-5 different prompt templates to generate diverse synthetic inputs. Diversity of the generation prompt matters more than the number of outputs — 5 prompts × 10 outputs each beats 1 prompt × 50 outputs.

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Template examples:
1. "Generate a {scenario} query where the user {action} with {constraint}"
2. "Write a frustrated customer message about {failure_mode}"
3. "Create an ambiguous query that could mean either {intent_a} or {intent_b}"
4. "Generate a query in {non_english_language} about {domain}"
5. "Create a query with a typo/misspelling about {domain}"

Critical rule: You generate inputs ONLY. Never generate labels. Labels must come from real system output + human judgment (or deterministic rules). An LLM generating both inputs and labels creates a self-consistency loop with artificially inflated accuracy.

Adversarial examples

For each dimension, generate 3 types of adversarial inputs:

1. Near-miss: Just barely on the wrong side of the pass/fail boundary. "Order #12345 was delivered yesterday" (when it was delivered today).
2. Confounder: Two dimensions conflict. Tone requires empathy but facts require correcting the customer's misunderstanding.
3. Distribution shift: Inputs from a domain or format rarely seen in training. New product category, different language, unusual formatting.

Labeling guide

If human annotation is needed, provide a template:

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## Annotation Task: [dimension_name]

**Criterion**: [what the dimension measures]

**Pass**: [concrete, observable conditions for pass]
**Fail**: [concrete, observable conditions for fail]

**Examples**:
- Input: "..." | Output: "..." | Judgment: Pass | Reason: ...
- Input: "..." | Output: "..." | Judgment: Fail | Reason: ...

**Edge cases**:
- If X happens but Y doesn't → [how to judge]
- If both A and B are present → [which takes priority]

Step 4: Output OpenJudge Dataset

Format the dataset for direct use with OpenJudge GradingRunner:

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# The standard dataset format accepted by GradingRunner.arun()
dataset = [
    {
        "query": "Where is my order #12345?",
        "response": "Your order #12345 was shipped on May 10 and is expected to arrive May 12.",
        "reference_response": "Order #12345: shipped May 10, ETA May 12. Tracking: 1Z999AA10123456784.",
        "context": "Order #12345 | Status: shipped | Date: 2026-05-10 | Carrier: UPS | Tracking: 1Z999AA10123456784",
        "metadata": {
            "difficulty": "easy",
            "dimension": "order_accuracy",
            "quadrant": "happy_path"
        }
    },
    {
        "query": "My package hasn't moved in 3 days, this is ridiculous",
        "response": "I understand your frustration. Let me check tracking for your recent orders.",
        "reference_response": None,
        "context": "Customer has 2 active orders: #12345 (in transit, last scan 2026-05-09), #12346 (processing)",
        "metadata": {
            "difficulty": "boundary",
            "dimension": "tone_appropriateness",
            "quadrant": "boundary"
        }
    },
]

Field reference

Output Files

After running this skill:

Common Mistakes

• Skipping stratification. A flat random sample is dominated by easy cases. Boundary degradation — the earliest warning sign — goes undetected.
• Generating labels with the same LLM that generates inputs. Creates a self-consistency loop. The judge and test data generator must be independent.
• Too few adversarial examples. 10% adversarial is the minimum. These are the cases that actually differentiate a robust system from a brittle one.
• No coverage analysis. When a dimension has < 5 test cases, you're not measuring it — you're guessing. Check per-dimension counts before declaring the dataset ready.
• Same prompt template for all synthetic data. Template diversity directly determines test diversity. Use at least 3 different generation prompts.

Next Skills

After 01-eval-design:

• 02-metric-design: You have a dataset. Now select graders and build the evaluation pipeline.
• 03-align-human: If you have human labels, calibrate your judge against them.
• 08-bootstrap: If you're still exploring and want a quick v0 grader before full dataset design.