/eval-driven-dev

Step 1c: Eval Criteria

Define what quality dimensions matter for this app — based on the project analysis (00-project-analysis.md) and the entry point (01-entry-point.md) you've already documented.

This document serves two purposes:

1. Dataset creation (Step 4): The use cases tell you what kinds of items to generate — each use case should have representative items in the dataset.
2. Evaluator selection (Step 3): The eval criteria tell you what evaluators to choose and how to map them.

Derive use cases from the capability inventory in pixie_qa/00-project-analysis.md. Derive eval criteria from the hard problems / failure modes — not generic quality dimensions like "factuality" or "relevance".

Keep this concise — it's a planning artifact, not a comprehensive spec.

What to define

1. Use cases

List the distinct scenarios the app handles. Derive these from the capability inventory in pixie_qa/00-project-analysis.md — each capability should map to at least one use case. Each use case becomes a category of dataset items. Each use case description must be a concise one-liner that conveys both (a) what the input is and (b) what the expected behavior or outcome is. The description should be specific enough that someone unfamiliar with the app can understand the scenario and its success criteria.

When possible, indicate the expected difficulty level for each use case — e.g., "routine" for straightforward cases, "challenging" for edge cases or failure-mode scenarios. This guides dataset creation (Step 4) to include entries across a range of difficulty levels rather than clustering at easy cases.

Good use case descriptions:

• "Reroute to human agent on account lookup difficulties"
• "Answer billing question using customer's plan details from CRM"
• "Decline to answer questions outside the support domain"
• "Summarize research findings including all queried sub-topics"

Bad use case descriptions (too vague):

• "Handle billing questions"
• "Edge case"
• "Error handling"

2. Eval criteria

Define high-level, application-specific eval criteria — quality dimensions that matter for THIS app. Each criterion will map to an evaluator in Step 3.

Good criteria are specific to the app's purpose and derived from the hard problems / failure modes in pixie_qa/00-project-analysis.md. Examples:

• Voice customer support agent: "Does the agent verify the caller's identity before transferring?", "Are responses concise enough for phone conversation?"
• Research report generator: "Does the report address all sub-questions?", "Are claims supported by retrieved sources?"
• RAG chatbot: "Are answers grounded in the retrieved context?", "Does it say 'I don't know' when context is missing?"
• Web scraper: "Does the extracted data match the requested schema fields?", "Does it handle malformed HTML without crashing or losing data?"

Bad criteria are generic evaluator names dressed up as requirements. Don't say "Factual accuracy" or "Response relevance" — say what factual accuracy or relevance means for THIS app. If your criteria could apply to any chatbot (e.g., "Groundedness", "PromptRelevance"), they're too generic — go back to the failure modes in 00-project-analysis.md and derive criteria from those.

At this stage, don't pick evaluator classes or thresholds. That comes in Step 3.

3. Check criteria applicability and observability

For each criterion:

1. Determine applicability scope — does this criterion apply to ALL use cases, or only a subset? If a criterion is only relevant for certain scenarios (e.g., "identity verification" only applies to account-related requests, not general FAQ), mark it clearly. This distinction is critical for Step 4 (dataset creation) because:

   • Universal criteria → become dataset-level default evaluators
   • Case-specific criteria → become item-level evaluators on relevant rows only

2. Verify observability — for each criterion, identify what data point in the app needs to be captured as a wrap() call to evaluate it. This drives the wrap coverage in Step 2.

   • If the criterion is about the app's final response → captured by wrap(purpose="output", name="response")
   • If it's about a routing decision → captured by wrap(purpose="state", name="routing_decision")
   • If it's about data the app fetched and used → captured by wrap(purpose="input", name="...")

Projects with multiple capabilities

If the project analysis (pixie_qa/00-project-analysis.md) lists multiple capabilities, you should evaluate at minimum the 2-3 most important / commonly used capabilities. Don't limit the dataset to a single capability when the project's value comes from breadth.

For each additional capability beyond the first:

• Add use cases in 02-eval-criteria.md
• Plan for a separate trace (run pixie trace with different entry points / configs) in Step 2
• Plan dataset entries covering that capability in Step 4

If time or context constraints make it impractical to cover all capabilities, document which ones you covered and which you skipped (with rationale) at the end of 02-eval-criteria.md.

Criteria quality gate (mandatory self-check)

Before writing 02-eval-criteria.md, run this check on every criterion:

For each criterion, ask: "If the app returned a structurally correct but semantically wrong or hallucinated answer, would this criterion catch it?"

• If the answer is "no" for ALL criteria, your criteria set is structural-only — it checks plumbing (fields exist, data flowed through) but not quality (content is correct, complete, non-hallucinated). You must add at least one semantic criterion that evaluates the content of the app's output, not just its shape.
• Structural criteria (field existence, JSON validity, format checks) are useful but insufficient. They pass even when the app returns fabricated or incorrect data.

Examples of structural vs semantic criteria:

A good criteria set has both structural and semantic criteria. Structural criteria catch gross failures (app crashed, returned empty output). Semantic criteria catch quality failures (app ran but returned wrong/hallucinated/incomplete content).

Output: pixie_qa/02-eval-criteria.md

Write your findings to this file. Keep it short — the template below is the maximum length.

Template

# Eval Criteria

## Use cases

1. <Use case name>: <one-liner conveying input + expected behavior>
2. ...

## Eval criteria

| #   | Criterion | Applies to    | Data to capture |
| --- | --------- | ------------- | --------------- |
| 1   | ...       | All           | wrap name: ...  |
| 2   | ...       | Use case 1, 3 | wrap name: ...  |

## Capability coverage

Capabilities covered: <list>
Capabilities skipped (with rationale): <list or "none">