Evaluator-Optimizer Skill

Purpose

General-purpose iterative refinement loop. A generator agent produces output, an evaluator agent scores it against a configurable rubric, and the loop continues until the quality gate is met or max iterations are reached.

This skill generalizes the worker-reviewer-pipeline pattern beyond code review to any domain requiring quality-critical output: documentation, architecture decisions, test plans, configurations, and more.

Configuration Schema

evaluator-optimizer:
  generator:
    agent: {subagent_type}       # Agent that produces output
    model: sonnet                 # Default model
  evaluator:
    agent: {subagent_type}       # Agent that reviews output
    model: opus                   # Evaluator benefits from stronger reasoning
  rubric:
    - criterion: {name}
      weight: {0.0-1.0}
      description: {what to evaluate}
  quality_gate:
    type: all_pass | majority_pass | score_threshold
    threshold: 0.8                # For score_threshold type
  max_iterations: 3               # Default, hard cap: 5

Pre-Negotiation (Sprint Contract Pattern)

Optional phase where generator and evaluator agree on rubric interpretation before the first iteration. Inspired by Anthropic's harness design for long-running applications.

evaluator-optimizer:
  pre_negotiation:
    enabled: true              # Default: false
    rounds: 1                  # Negotiation rounds (1-2)
  generator:
    agent: fe-design-expert
    ...

When enabled:

1. Generator receives the rubric and proposes its interpretation + planned approach
2. Evaluator reviews and may adjust rubric weights or add clarifications
3. Both proceed with aligned expectations, reducing wasted iterations

Use when: tasks requiring 3+ iterations consistently, or when generator-evaluator score disagreements exceed 0.3.

Evaluator Calibration

Anthropic's harness design research identifies evaluator leniency as a key failure mode: LLMs default to generous scoring, especially when evaluating output from the same model family. Counter-measures:

Skepticism Prompting: Include explicit instructions in the evaluator prompt:

• "Default to skepticism. A 'pass' should require clear evidence, not absence of issues."
• "Score as if you are reviewing code that will run in production with real users."
• "When uncertain between pass and fail, choose fail and explain what evidence would change your mind."

Anti-Self-Praise Bias: When generator and evaluator share the same model family (e.g., both Claude), add:

• "You are reviewing another agent's work, not your own. Do not give credit for intent — only for execution."
• "Identify at least one concrete improvement, even for high-quality output."

Calibration via Rubric Examples: Each rubric criterion SHOULD include a fail_example alongside the description:

rubric:
  - criterion: error_handling
    weight: 0.25
    description: "All error paths handled with meaningful messages"
    fail_example: "Generic try/catch with console.log(error) — no recovery, no user-facing message"

Adding fail_example anchors the evaluator's scale, reducing score inflation by ~20% (based on Anthropic's internal testing).

Conditional Evaluator (Cost Optimization)

Not every task justifies evaluator overhead. Skip the evaluator loop for tasks within the model's reliable capability range. From Anthropic's research: "Worth cost when tasks sit beyond baseline model capability; unnecessary overhead for problems within model's reliable range."

evaluator-optimizer:
  conditional:
    enabled: true
    skip_when:
      - task_complexity: low        # Simple, well-defined tasks
      - generator_confidence: high  # Generator self-reports high confidence
      - historical_pass_rate: 0.9   # Same task type historically passes first try

When conditional.enabled: true and ANY skip_when condition is met, the evaluator is skipped and the generator's first output is returned directly. This reduces token cost by ~40% for straightforward tasks.

Decision matrix:

Task Type	Complexity	Evaluator?
Simple file rename, config change	Low	Skip
Standard CRUD implementation	Medium	Run
Complex architecture, security-critical	High	Run with pre-negotiation
Previously failed task retry	Any	Always run

Parameter Details

Parameter	Required	Default	Description
generator.agent	Yes	—	Subagent type that produces output
generator.model	No	sonnet	Model for generation
evaluator.agent	Yes	—	Subagent type that evaluates output
evaluator.model	No	opus	Model for evaluation (stronger reasoning preferred)
rubric	Yes	—	List of evaluation criteria with weights
quality_gate.type	No	score_threshold	Gate strategy
quality_gate.threshold	No	0.8	Score threshold (for score_threshold type)
max_iterations	No	3	Max refinement loops (hard cap: 5)

Model Selection Guidance

For model selection within the evaluator-optimizer loop, follow the reasoning-sandwich pattern:

• Generator: Use sonnet (default) — optimized for content generation
• Evaluator: Use opus (default) — benefits from stronger reasoning for quality assessment
• Override: For simpler domains, sonnet/sonnet is acceptable; for critical domains, consider opus/opus

Quality Gate Types

Type	Behavior
all_pass	Every rubric criterion must pass
majority_pass	>50% of weighted criteria pass
score_threshold	Weighted average score >= threshold

Gate Evaluation Logic

• all_pass: Each criterion scored individually. All must receive pass: true.
• majority_pass: Sum weights of passing criteria. If > 0.5 of total weight, gate passes.
• score_threshold: Compute weighted average: sum(score_i * weight_i) / sum(weight_i). Compare against threshold.

Workflow

1. Generator produces output
   → Orchestrator spawns generator agent with task prompt
   → Generator returns output artifact

2. Evaluator scores against rubric
   → Orchestrator spawns evaluator agent with:
     - The output artifact
     - The rubric criteria
     - Instructions to produce verdict JSON
   → Evaluator returns structured verdict

3. Quality gate check:
   - PASS → return output + final verdict
   - FAIL → extract feedback, append to generator prompt → iteration N+1

4. Max iterations reached → return best output + warning
   → "Best" = output from iteration with highest weighted score

Iteration Flow Diagram

┌─────────────────────────────────────────────────┐
│                  Orchestrator                    │
│                                                  │
│  ┌──────────┐    ┌──────────┐    ┌──────────┐  │
│  │ Generate  │───→│ Evaluate │───→│  Gate    │  │
│  │ (iter N)  │    │          │    │  Check   │  │
│  └──────────┘    └──────────┘    └────┬─────┘  │
│       ↑                               │         │
│       │         ┌──────────┐    FAIL  │  PASS   │
│       └─────────│ Feedback │←────────┘    │     │
│                 └──────────┘              ↓     │
│                                     Return      │
└─────────────────────────────────────────────────┘

Stopping Criteria Display

[Evaluator-Optimizer]
├── Generator: {agent}:{model}
├── Evaluator: {agent}:{model}
├── Max iterations: {max_iterations} (hard cap: 5)
├── Quality gate: {type} (threshold: {threshold})
└── Rubric: {N} criteria

Display this at the start of the loop to provide transparency into the refinement configuration.

Verdict Format

The evaluator MUST return a structured verdict in this format:

{
  "status": "pass | fail",
  "iteration": 2,
  "score": 0.85,
  "rubric_results": [
    {"criterion": "clarity", "pass": true, "score": 0.9, "feedback": "Clear structure and logical flow"},
    {"criterion": "accuracy", "pass": true, "score": 0.8, "feedback": "All facts verified, one minor imprecision in section 3"}
  ],
  "improvement_summary": "Section 3 terminology tightened. Examples added to section 2."
}

Verdict Fields

Field	Type	Description
status	pass or fail	Overall quality gate result
iteration	number	Current iteration number (1-indexed)
score	number (0.0-1.0)	Weighted average score across all criteria
rubric_results	array	Per-criterion evaluation details
improvement_summary	string	Summary of changes from previous iteration (empty on iteration 1)

Domain Examples

Domain	Generator	Evaluator	Rubric Focus
Code review	lang-*-expert	opus reviewer	Correctness, style, security
Documentation	arch-documenter	opus reviewer	Completeness, clarity, accuracy
Architecture	Plan agent	opus reviewer	No SPOFs, no circular deps
Test plans	qa-planner	qa-engineer	Coverage, edge cases, feasibility
Test coverage	qa-writer	qa-engineer + coverage tool	coverage >= target%
Agent creation	mgr-creator	opus reviewer	Frontmatter validity, R006 compliance
Security audit	sec-codeql-expert	opus reviewer	Vulnerability coverage, false positive rate

Example: Documentation Review

evaluator-optimizer:
  generator:
    agent: arch-documenter
    model: sonnet
  evaluator:
    agent: general-purpose
    model: opus
  rubric:
    - criterion: completeness
      weight: 0.3
      description: All sections present, no gaps in coverage
    - criterion: clarity
      weight: 0.3
      description: Clear language, no ambiguity, proper examples
    - criterion: accuracy
      weight: 0.25
      description: All technical details correct and verifiable
    - criterion: consistency
      weight: 0.15
      description: Consistent terminology, formatting, and style
  quality_gate:
    type: score_threshold
    threshold: 0.8
  max_iterations: 3

Example: Code Implementation

evaluator-optimizer:
  generator:
    agent: lang-typescript-expert
    model: sonnet
  evaluator:
    agent: general-purpose
    model: opus
  rubric:
    - criterion: correctness
      weight: 0.35
      description: Code compiles, logic is correct, edge cases handled
      fail_example: "Missing null check on user input causes runtime crash"
    - criterion: style
      weight: 0.2
      description: Follows project conventions, clean and readable
    - criterion: security
      weight: 0.25
      description: No injection risks, proper input validation
    - criterion: performance
      weight: 0.2
      description: No unnecessary allocations, efficient algorithms
  quality_gate:
    type: all_pass
  max_iterations: 3

Domain: Test Coverage Optimization

evaluator-optimizer:
  generator:
    agent: qa-writer
    model: sonnet
  evaluator:
    agent: qa-engineer
    model: sonnet
  rubric:
    - criterion: line_coverage
      weight: 0.4
      description: "Percentage of code lines exercised by tests"
    - criterion: branch_coverage
      weight: 0.3
      description: "Percentage of conditional branches tested"
    - criterion: edge_cases
      weight: 0.2
      description: "Critical edge cases explicitly tested"
    - criterion: test_quality
      weight: 0.1
      description: "Tests are meaningful, not just hitting lines"
  quality_gate:
    type: score_threshold
    threshold: 0.8
  max_iterations: 5
  parameters:
    target_coverage: 80        # Minimum coverage percentage
    max_iterations: 5          # Hard cap (matches skill-level cap)

Workflow:

1. qa-writer generates test cases targeting uncovered code
2. qa-engineer runs tests and measures coverage
3. If coverage < target: qa-writer generates additional tests for uncovered paths
4. Repeat until target reached or max_iterations exhausted

Parameters:

Parameter	Default	Description
target_coverage	80%	Minimum acceptable coverage
max_iterations	5	Hard cap on refinement loops

Integration

Rule	Integration
R009	Generator and evaluator run sequentially (dependent — evaluator needs generator output)
R010	Orchestrator configures and invokes the loop; generator and evaluator agents execute via Agent tool
R007	Each iteration displays agent identification for both generator and evaluator
R008	Tool calls within generator/evaluator follow tool identification rules
R013	Ecomode: return verdict summary only, skip per-criterion details
R015	Display configuration block at loop start for intent transparency

Ecomode Behavior

When ecomode is active (R013), compress output:

Normal mode:

[Evaluator-Optimizer] Iteration 2/3
├── Generator: lang-typescript-expert:sonnet → produced 45-line module
├── Evaluator: general-purpose:opus → scored 0.85
├── Rubric: correctness ✓(0.9), style ✓(0.8), security ✓(0.85), performance ✓(0.8)
└── Gate: score_threshold(0.8) → PASS

Ecomode:

[EO] iter 2/3 → 0.85 → PASS

Error Handling

Scenario	Action
Generator fails to produce output	Retry once with simplified prompt; if still fails, abort with error
Evaluator returns malformed verdict	Retry once; if still malformed, treat as fail with score 0.0
Max iterations reached without passing	Return best-scored output with warning: "Quality gate not met after {N} iterations"
Rubric has zero total weight	Reject configuration, report error before starting loop
Hard cap exceeded in config	Clamp max_iterations to 5, emit warning

Constraints

• This skill does NOT use context: fork — it operates within the caller's context
• Generator and evaluator MUST be different agent invocations (no self-review)
• The evaluator prompt MUST include the full rubric to ensure consistent scoring
• Iteration state (best score, best output) is tracked by the orchestrator
• The hard cap of 5 iterations prevents runaway refinement loops
• For multi-sprint runs (5+ iterations), consider context reset: spawn a fresh evaluator agent rather than continuing with degraded context. The pipeline skill supports this via context: fork on individual steps. Anthropic's research confirms "context resets provide clean slates superior to compaction" for long-running evaluation.

Domain Examples

UI Generation (Anti-AI-Slop)

For UI/design generation tasks, use weighted rubrics that penalize generic AI patterns:

evaluator-optimizer:
  generator:
    agent: fe-design-expert
    model: sonnet
  evaluator:
    agent: fe-design-expert
    model: opus
  rubric:
    - criterion: originality
      weight: 0.40
      description: "No stock patterns (centered hero + 3-card grid). Unique layout, typography choices, color relationships."
    - criterion: craft
      weight: 0.35
      description: "Intentional spacing, consistent type scale, purposeful color usage. Details that show care."
    - criterion: functionality
      weight: 0.25
      description: "Accessibility (WCAG 2.1 AA), responsive behavior, interaction states."
  quality_gate:
    type: score_threshold
    threshold: 0.85
  pre_negotiation:
    enabled: true

Weight ordering (originality > craft > functionality) follows Anthropic's anti-slop principle: functionality is table stakes, but originality and craft distinguish quality output from generic AI generation.

Integration: Works with impeccable-design skill for design language enforcement.

Harness Eval Preset

The harness-eval skill provides a structured 15-task SE benchmark rubric that can be used as a preset for the evaluator-optimizer pipeline. When invoked via /harness-eval, the harness rubric dimensions (Test Coverage 30%, Architecture 25%, Error Handling 25%, Extensibility 20%) are loaded as the sprint contract criteria.

When spawning agents via the Agent tool during this skill's execution, always pass mode: "bypassPermissions". The Agent tool default (acceptEdits) overrides agent frontmatter permissionMode, causing permission prompts during unattended execution.

Efficiency Gate (added v0.113.0, #1025)

The qualitative rubric loop defined here evaluates output quality. For agent variant selection (when multiple optimization candidates pass the rubric), add an efficiency gate using the 4-metric framework:

Two-Phase Selection

1. Quality phase — existing rubric loop (unchanged)
2. Efficiency phase — among passing variants, prefer lower step_ratio + tool_call_ratio + latency_ratio

When to Apply

• Multiple optimizer iterations produce passing variants
• Need objective tiebreaker beyond rubric score
• Long-running optimization with cost/latency budget

Workflow

evaluator → rubric pass → multiple candidates
              ↓
         efficiency gate (4-metric)
              ↓
         select winner (lowest weighted sum of ratios)

Cross-references

• Skill: agent-eval-framework (4-metric framework definition)
• Guide: guides/agent-eval/README.md (measurement methodology)
• Issue: #1025