| name | skill-judge |
| description | Evaluate Agent Skill design quality against official specifications and best practices. Use when reviewing, auditing, or improving SKILL.md files and skill packages. Provides multi-dimensional scoring and actionable improvement suggestions. |
Skill Judge
Evaluate Agent Skills against official specifications and patterns derived from 17+ official examples.
Core Philosophy
What is a Skill?
A Skill is NOT a tutorial. A Skill is a knowledge externalization mechanism.
Traditional AI knowledge is locked in model parameters. To teach new capabilities:
Traditional: Collect data → GPU cluster → Train → Deploy new version
Cost: $10,000 - $1,000,000+
Timeline: Weeks to months
Skills change this:
Skill: Edit SKILL.md → Save → Takes effect on next invocation
Cost: $0
Timeline: Instant
This is the paradigm shift from "training AI" to "educating AI" — like a hot-swappable LoRA adapter that requires no training. You edit a Markdown file in natural language, and the model's behavior changes.
The Core Formula
Good Skill = Expert-only Knowledge − What Claude Already Knows
A Skill's value is measured by its knowledge delta — the gap between what it provides and what the model already knows.
- Expert-only knowledge: Decision trees, trade-offs, edge cases, anti-patterns, domain-specific thinking frameworks — things that take years of experience to accumulate
- What Claude already knows: Basic concepts, standard library usage, common programming patterns, general best practices
When a Skill explains "what is PDF" or "how to write a for-loop", it's compressing knowledge Claude already has. This is token waste — context window is a public resource shared with system prompts, conversation history, other Skills, and user requests.
Tool vs Skill
| Concept | Essence | Function | Example |
|---|
| Tool | What model CAN do | Execute actions | bash, read_file, write_file, WebSearch |
| Skill | What model KNOWS how to do | Guide decisions | PDF processing, MCP building, frontend design |
Tools define capability boundaries — without bash tool, model can't execute commands.
Skills inject knowledge — without frontend-design Skill, model produces generic UI.
The equation:
General Agent + Excellent Skill = Domain Expert Agent
Same Claude model, different Skills loaded, becomes different experts.
Three Types of Knowledge in Skills
When evaluating, categorize each section:
| Type | Definition | Treatment |
|---|
| Expert | Claude genuinely doesn't know this | Must keep — this is the Skill's value |
| Activation | Claude knows but may not think of | Keep if brief — serves as reminder |
| Redundant | Claude definitely knows this | Should delete — wastes tokens |
The art of Skill design is maximizing Expert content, using Activation sparingly, and eliminating Redundant ruthlessly.
Evaluation Dimensions (120 points total)
D1: Knowledge Delta (20 points) — THE CORE DIMENSION
The most important dimension. Does the Skill add genuine expert knowledge?
| Score | Criteria |
|---|
| 0-5 | Explains basics Claude knows (what is X, how to write code, standard library tutorials) |
| 6-10 | Mixed: some expert knowledge diluted by obvious content |
| 11-15 | Mostly expert knowledge with minimal redundancy |
| 16-20 | Pure knowledge delta — every paragraph earns its tokens |
Red flags (instant score ≤5):
- "What is [basic concept]" sections
- Step-by-step tutorials for standard operations
- Explaining how to use common libraries
- Generic best practices ("write clean code", "handle errors")
- Definitions of industry-standard terms
Green flags (indicators of high knowledge delta):
- Decision trees for non-obvious choices ("when X fails, try Y because Z")
- Trade-offs only an expert would know ("A is faster but B handles edge case C")
- Edge cases from real-world experience
- "NEVER do X because [non-obvious reason]"
- Domain-specific thinking frameworks
Evaluation questions:
- For each section, ask: "Does Claude already know this?"
- If explaining something, ask: "Is this explaining TO Claude or FOR Claude?"
- Count paragraphs that are Expert vs Activation vs Redundant
D2: Mindset + Appropriate Procedures (15 points)
Does the Skill transfer expert thinking patterns along with necessary domain-specific procedures?
The difference between experts and novices isn't "knowing how to operate" — it's "how to think about the problem." But thinking patterns alone aren't enough when Claude lacks domain-specific procedural knowledge.
Key distinction:
| Type | Example | Value |
|---|
| Thinking patterns | "Before designing, ask: What makes this memorable?" | High — shapes decision-making |
| Domain-specific procedures | "OOXML workflow: unpack → edit XML → validate → pack" | High — Claude may not know this |
| Generic procedures | "Step 1: Open file, Step 2: Edit, Step 3: Save" | Low — Claude already knows |
| Score | Criteria |
|---|
| 0-3 | Only generic procedures Claude already knows |
| 4-7 | Has domain procedures but lacks thinking frameworks |
| 8-11 | Good balance: thinking patterns + domain-specific workflows |
| 12-15 | Expert-level: shapes thinking AND provides procedures Claude wouldn't know |
What counts as valuable procedures:
- Workflows Claude hasn't been trained on (new tools, proprietary systems)
- Correct ordering that's non-obvious (e.g., "validate BEFORE packing, not after")
- Critical steps that are easy to miss (e.g., "MUST recalculate formulas after editing")
- Domain-specific sequences (e.g., MCP server's 4-phase development process)
What counts as redundant procedures:
- Generic file operations (open, read, write, save)
- Standard programming patterns (loops, conditionals, error handling)
- Common library usage that's well-documented
Expert thinking patterns look like:
Before [action], ask yourself:
- **Purpose**: What problem does this solve? Who uses it?
- **Constraints**: What are the hidden requirements?
- **Differentiation**: What makes this solution memorable?
Valuable domain procedures look like:
### Redlining Workflow (Claude wouldn't know this sequence)
1. Convert to markdown: `pandoc --track-changes=all`
2. Map text to XML: grep for text in document.xml
3. Implement changes in batches of 3-10
4. Pack and verify: check ALL changes were applied
Redundant generic procedures look like:
Step 1: Open the file
Step 2: Find the section
Step 3: Make the change
Step 4: Save and test
The test:
- Does it tell Claude WHAT to think about? (thinking patterns)
- Does it tell Claude HOW to do things it wouldn't know? (domain procedures)
A good Skill provides both when needed.
D3: Anti-Pattern Quality (15 points)
Does the Skill have effective NEVER lists?
Why this matters: Half of expert knowledge is knowing what NOT to do. A senior designer sees purple gradient on white background and instinctively cringes — "too AI-generated." This intuition for "what absolutely not to do" comes from stepping on countless landmines.
Claude hasn't stepped on these landmines. It doesn't know Inter font is overused, doesn't know purple gradients are the signature of AI-generated content. Good Skills must explicitly state these "absolute don'ts."
| Score | Criteria |
|---|
| 0-3 | No anti-patterns mentioned |
| 4-7 | Generic warnings ("avoid errors", "be careful", "consider edge cases") |
| 8-11 | Specific NEVER list with some reasoning |
| 12-15 | Expert-grade anti-patterns with WHY — things only experience teaches |
Expert anti-patterns (specific + reason):
NEVER use generic AI-generated aesthetics like:
- Overused font families (Inter, Roboto, Arial)
- Cliched color schemes (particularly purple gradients on white backgrounds)
- Predictable layouts and component patterns
- Default border-radius on everything
Weak anti-patterns (vague, no reasoning):
Avoid making mistakes.
Be careful with edge cases.
Don't write bad code.
The test: Would an expert read the anti-pattern list and say "yes, I learned this the hard way"? Or would they say "this is obvious to everyone"?
D4: Specification Compliance — Especially Description (15 points)
Does the Skill follow official format requirements? Special focus on description quality.
| Score | Criteria |
|---|
| 0-5 | Missing frontmatter or invalid format |
| 6-10 | Has frontmatter but description is vague or incomplete |
| 11-13 | Valid frontmatter, description has WHAT but weak on WHEN |
| 14-15 | Perfect: comprehensive description with WHAT, WHEN, and trigger keywords |
Frontmatter requirements:
name: lowercase, alphanumeric + hyphens only, ≤64 charactersdescription: THE MOST CRITICAL FIELD — determines if skill gets used at all
Why description is THE MOST IMPORTANT field:
┌─────────────────────────────────────────────────────────────────────┐
│ SKILL ACTIVATION FLOW │
│ │
│ User Request → Agent sees ALL skill descriptions → Decides which │
│ (only descriptions, not bodies!) to activate │
│ │
│ If description doesn't match → Skill NEVER gets loaded │
│ If description is vague → Skill might not trigger when it should │
│ If description lacks keywords → Skill is invisible to the Agent │
└─────────────────────────────────────────────────────────────────────┘
The brutal truth: A Skill with perfect content but poor description is useless — it will never be activated. The description is the only chance to tell the Agent "use me in these situations."
Description must answer THREE questions:
- WHAT: What does this Skill do? (functionality)
- WHEN: In what situations should it be used? (trigger scenarios)
- KEYWORDS: What terms should trigger this Skill? (searchable terms)
Excellent description (all three elements):
description: "Comprehensive document creation, editing, and analysis with support
for tracked changes, comments, formatting preservation, and text extraction.
When Claude needs to work with professional documents (.docx files) for:
(1) Creating new documents, (2) Modifying or editing content,
(3) Working with tracked changes, (4) Adding comments, or any other document tasks"
Analysis:
- WHAT: creation, editing, analysis, tracked changes, comments
- WHEN: "When Claude needs to work with... for: (1)... (2)... (3)..."
- KEYWORDS: .docx files, tracked changes, professional documents
Poor description (missing elements):
description: "Handles document-related features"
Problems:
- WHAT: vague ("document-related features" — what specifically?)
- WHEN: missing (when should Agent use this?)
- KEYWORDS: missing (no ".docx", no specific scenarios)
Another poor example:
description: "A helpful skill for various tasks"
This is useless — Agent has no idea when to activate it.
Description quality checklist:
D5: Progressive Disclosure (15 points)
Does the Skill implement proper content layering?
Skill loading has three layers:
Layer 1: Metadata (always in memory)
Only name + description
~100 tokens per skill
Layer 2: SKILL.md Body (loaded after triggering)
Detailed guidelines, code examples, decision trees
Ideal: < 500 lines
Layer 3: Resources (loaded on demand)
scripts/, references/, assets/
No limit
| Score | Criteria |
|---|
| 0-5 | Everything dumped in SKILL.md (>500 lines, no structure) |
| 6-10 | Has references but unclear when to load them |
| 11-13 | Good layering with MANDATORY triggers present |
| 14-15 | Perfect: decision trees + explicit triggers + "Do NOT Load" guidance |
For Skills WITH references directory, check Loading Trigger Quality:
| Trigger Quality | Characteristics |
|---|
| Poor | References listed at end, no loading guidance |
| Mediocre | Some triggers but not embedded in workflow |
| Good | MANDATORY triggers in workflow steps |
| Excellent | Scenario detection + conditional triggers + "Do NOT Load" |
The loading problem:
Loading too little ◄─────────────────────────────────► Loading too much
- References sit unused - Wastes context space
- Agent doesn't know when to load - Irrelevant info dilutes key content
- Knowledge is there but never accessed - Unnecessary token overhead
Good loading trigger (embedded in workflow):
### Creating New Document
**MANDATORY - READ ENTIRE FILE**: Before proceeding, you MUST read
[`docx-js.md`](docx-js.md) (~500 lines) completely from start to finish.
**NEVER set any range limits when reading this file.**
**Do NOT load** `ooxml.md` or `redlining.md` for this task.
Bad loading trigger (just listed):
## References
- docx-js.md - for creating documents
- ooxml.md - for editing
- redlining.md - for tracking changes
For simple Skills (no references, <100 lines): Score based on conciseness and self-containment.
D6: Freedom Calibration (15 points)
Is the level of specificity appropriate for the task's fragility?
Different tasks need different levels of constraint. This is about matching freedom to fragility.
| Score | Criteria |
|---|
| 0-5 | Severely mismatched (rigid scripts for creative tasks, vague for fragile ops) |
| 6-10 | Partially appropriate, some mismatches |
| 11-13 | Good calibration for most scenarios |
| 14-15 | Perfect freedom calibration throughout |
The freedom spectrum:
| Task Type | Should Have | Why | Example Skill |
|---|
| Creative/Design | High freedom | Multiple valid approaches, differentiation is value | frontend-design |
| Code review | Medium freedom | Principles exist but judgment required | code-review |
| File format operations | Low freedom | One wrong byte corrupts file, consistency critical | docx, xlsx, pdf |
High freedom (text-based instructions):
Commit to a BOLD aesthetic direction. Pick an extreme: brutally minimal,
maximalist chaos, retro-futuristic, organic natural...
Medium freedom (pseudocode or parameterized):
Review priority:
1. Security vulnerabilities (must fix)
2. Logic errors (must fix)
3. Performance issues (should fix)
4. Maintainability (optional)
Low freedom (specific scripts, exact steps):
**MANDATORY**: Use exact script in `scripts/create-doc.py`
Parameters: --title "X" --author "Y"
Do NOT modify the script.
The test: Ask "if Agent makes a mistake, what's the consequence?"
- High consequence → Low freedom
- Low consequence → High freedom
D7: Pattern Recognition (10 points)
Does the Skill follow an established official pattern?
Through analyzing 17 official Skills, we identified 5 main design patterns:
| Pattern | ~Lines | Key Characteristics | Example | When to Use |
|---|
| Mindset | ~50 | Thinking > technique, strong NEVER list, high freedom | frontend-design | Creative tasks requiring taste |
| Navigation | ~30 | Minimal SKILL.md, routes to sub-files | internal-comms | Multiple distinct scenarios |
| Philosophy | ~150 | Two-step: Philosophy → Express, emphasizes craft | canvas-design | Art/creation requiring originality |
| Process | ~200 | Phased workflow, checkpoints, medium freedom | mcp-builder | Complex multi-step projects |
| Tool | ~300 | Decision trees, code examples, low freedom | docx, pdf, xlsx | Precise operations on specific formats |
| Score | Criteria |
|---|
| 0-3 | No recognizable pattern, chaotic structure |
| 4-6 | Partially follows a pattern with significant deviations |
| 7-8 | Clear pattern with minor deviations |
| 9-10 | Masterful application of appropriate pattern |
Pattern selection guide:
| Your Task Characteristics | Recommended Pattern |
|---|
| Needs taste and creativity | Mindset (~50 lines) |
| Needs originality and craft quality | Philosophy (~150 lines) |
| Has multiple distinct sub-scenarios | Navigation (~30 lines) |
| Complex multi-step project | Process (~200 lines) |
| Precise operations on specific format | Tool (~300 lines) |
D8: Practical Usability (15 points)
Can an Agent actually use this Skill effectively?
| Score | Criteria |
|---|
| 0-5 | Confusing, incomplete, contradictory, or untested guidance |
| 6-10 | Usable but with noticeable gaps |
| 11-13 | Clear guidance for common cases |
| 14-15 | Comprehensive coverage including edge cases and error handling |
Check for:
- Decision trees: For multi-path scenarios, is there clear guidance on which path to take?
- Code examples: Do they actually work? Or are they pseudocode that breaks?
- Error handling: What if the main approach fails? Are fallbacks provided?
- Edge cases: Are unusual but realistic scenarios covered?
- Actionability: Can Agent immediately act, or needs to figure things out?
Good usability (decision tree + fallback):
| Task | Primary Tool | Fallback | When to Use Fallback |
| -------------- | ------------ | --------- | -------------------- |
| Read text | pdftotext | PyMuPDF | Need layout info |
| Extract tables | camelot-py | tabula-py | camelot fails |
**Common issues**:
- Scanned PDF: pdftotext returns blank → Use OCR first
- Encrypted PDF: Permission error → Use PyMuPDF with password
Poor usability (vague):
Use appropriate tools for PDF processing.
Handle errors properly.
Consider edge cases.
NEVER Do When Evaluating
- NEVER give high scores just because it "looks professional" or is well-formatted
- NEVER ignore token waste — every redundant paragraph should result in deduction
- NEVER let length impress you — a 43-line Skill can outperform a 500-line Skill
- NEVER skip mentally testing the decision trees — do they actually lead to correct choices?
- NEVER forgive explaining basics with "but it provides helpful context"
- NEVER overlook missing anti-patterns — if there's no NEVER list, that's a significant gap
- NEVER assume all procedures are valuable — distinguish domain-specific from generic
- NEVER undervalue the description field — poor description = skill never gets used
- NEVER put "when to use" info only in the body — Agent only sees description before loading
Evaluation Protocol
Step 1: First Pass — Knowledge Delta Scan
Read SKILL.md completely and for each section ask:
"Does Claude already know this?"
Mark each section as:
- [E] Expert: Claude genuinely doesn't know this — value-add
- [A] Activation: Claude knows but brief reminder is useful — acceptable
- [R] Redundant: Claude definitely knows this — should be deleted
Calculate rough ratio: E:A:R
- Good Skill: >70% Expert, <20% Activation, <10% Redundant
- Mediocre Skill: 40-70% Expert, high Activation
- Bad Skill: <40% Expert, high Redundant
Step 2: Structure Analysis
[ ] Check frontmatter validity
[ ] Count total lines in SKILL.md
[ ] List all reference files and their sizes
[ ] Identify which pattern the Skill follows
[ ] Check for loading triggers (if references exist)
Step 3: Score Each Dimension
For each of the 8 dimensions:
- Find specific evidence (quote relevant lines)
- Assign score with one-line justification
- Note specific improvements if score < max
Step 4: Calculate Total & Grade
Total = D1 + D2 + D3 + D4 + D5 + D6 + D7 + D8
Max = 120 points
Grade Scale (percentage-based):
| Grade | Percentage | Meaning |
|---|
| A | 90%+ (108+) | Excellent — production-ready expert Skill |
| B | 80-89% (96-107) | Good — minor improvements needed |
| C | 70-79% (84-95) | Adequate — clear improvement path |
| D | 60-69% (72-83) | Below Average — significant issues |
| F | <60% (<72) | Poor — needs fundamental redesign |
Step 5: Generate Report
# Skill Evaluation Report: [Skill Name]
## Summary
- **Total Score**: X/120 (X%)
- **Grade**: [A/B/C/D/F]
- **Pattern**: [Mindset/Navigation/Philosophy/Process/Tool]
- **Knowledge Ratio**: E:A:R = X:Y:Z
- **Verdict**: [One sentence assessment]
## Dimension Scores
| Dimension | Score | Max | Notes |
| ---------------------------- | ----- | --- | ----- |
| D1: Knowledge Delta | X | 20 | |
| D2: Mindset vs Mechanics | X | 15 | |
| D3: Anti-Pattern Quality | X | 15 | |
| D4: Specification Compliance | X | 15 | |
| D5: Progressive Disclosure | X | 15 | |
| D6: Freedom Calibration | X | 15 | |
| D7: Pattern Recognition | X | 10 | |
| D8: Practical Usability | X | 15 | |
## Critical Issues
[List must-fix problems that significantly impact the Skill's effectiveness]
## Top 3 Improvements
1. [Highest impact improvement with specific guidance]
2. [Second priority improvement]
3. [Third priority improvement]
## Detailed Analysis
[For each dimension scoring below 80%, provide:
- What's missing or problematic
- Specific examples from the Skill
- Concrete suggestions for improvement]
Common Failure Patterns
Pattern 1: The Tutorial
Symptom: Explains what PDF is, how Python works, basic library usage
Root cause: Author assumes Skill should "teach" the model
Fix: Claude already knows this. Delete all basic explanations.
Focus on expert decisions, trade-offs, and anti-patterns.
Pattern 2: The Dump
Symptom: SKILL.md is 800+ lines with everything included
Root cause: No progressive disclosure design
Fix: Core routing and decision trees in SKILL.md (<300 lines ideal)
Detailed content in references/, loaded on-demand
Pattern 3: The Orphan References
Symptom: References directory exists but files are never loaded
Root cause: No explicit loading triggers
Fix: Add "MANDATORY - READ ENTIRE FILE" at workflow decision points
Add "Do NOT Load" to prevent over-loading
Pattern 4: The Checkbox Procedure
Symptom: Step 1, Step 2, Step 3... mechanical procedures
Root cause: Author thinks in procedures, not thinking frameworks
Fix: Transform into "Before doing X, ask yourself..."
Focus on decision principles, not operation sequences
Pattern 5: The Vague Warning
Symptom: "Be careful", "avoid errors", "consider edge cases"
Root cause: Author knows things can go wrong but hasn't articulated specifics
Fix: Specific NEVER list with concrete examples and non-obvious reasons
"NEVER use X because [specific problem that takes experience to learn]"
Pattern 6: The Invisible Skill
Symptom: Great content but skill rarely gets activated
Root cause: Description is vague, missing keywords, or lacks trigger scenarios
Fix: Description must answer WHAT, WHEN, and include KEYWORDS
"Use when..." + specific scenarios + searchable terms
Example fix:
BAD: "Helps with document tasks"
GOOD: "Create, edit, and analyze .docx files. Use when working with
Word documents, tracked changes, or professional document formatting."
Pattern 7: The Wrong Location
Symptom: "When to use this Skill" section in body, not in description
Root cause: Misunderstanding of three-layer loading
Fix: Move all triggering information to description field
Body is only loaded AFTER triggering decision is made
Pattern 8: The Over-Engineered
Symptom: README.md, CHANGELOG.md, INSTALLATION_GUIDE.md, CONTRIBUTING.md
Root cause: Treating Skill like a software project
Fix: Delete all auxiliary files. Only include what Agent needs for the task.
No documentation about the Skill itself.
Pattern 9: The Freedom Mismatch
Symptom: Rigid scripts for creative tasks, vague guidance for fragile operations
Root cause: Not considering task fragility
Fix: High freedom for creative (principles, not steps)
Low freedom for fragile (exact scripts, no parameters)
Quick Reference Checklist
┌─────────────────────────────────────────────────────────────────────────┐
│ SKILL EVALUATION QUICK CHECK │
├─────────────────────────────────────────────────────────────────────────┤
│ │
│ KNOWLEDGE DELTA (most important): │
│ [ ] No "What is X" explanations for basic concepts │
│ [ ] No step-by-step tutorials for standard operations │
│ [ ] Has decision trees for non-obvious choices │
│ [ ] Has trade-offs only experts would know │
│ [ ] Has edge cases from real-world experience │
│ │
│ MINDSET + PROCEDURES: │
│ [ ] Transfers thinking patterns (how to think about problems) │
│ [ ] Has "Before doing X, ask yourself..." frameworks │
│ [ ] Includes domain-specific procedures Claude wouldn't know │
│ [ ] Distinguishes valuable procedures from generic ones │
│ │
│ ANTI-PATTERNS: │
│ [ ] Has explicit NEVER list │
│ [ ] Anti-patterns are specific, not vague │
│ [ ] Includes WHY (non-obvious reasons) │
│ │
│ SPECIFICATION (description is critical!): │
│ [ ] Valid YAML frontmatter │
│ [ ] name: lowercase, ≤64 chars │
│ [ ] description answers: WHAT does it do? │
│ [ ] description answers: WHEN should it be used? │
│ [ ] description contains trigger KEYWORDS │
│ [ ] description is specific enough for Agent to know when to use │
│ │
│ STRUCTURE: │
│ [ ] SKILL.md < 500 lines (ideal < 300) │
│ [ ] Heavy content in references/ │
│ [ ] Loading triggers embedded in workflow │
│ [ ] Has "Do NOT Load" for preventing over-loading │
│ │
│ FREEDOM: │
│ [ ] Creative tasks → High freedom (principles) │
│ [ ] Fragile operations → Low freedom (exact scripts) │
│ │
│ USABILITY: │
│ [ ] Decision trees for multi-path scenarios │
│ [ ] Working code examples │
│ [ ] Error handling and fallbacks │
│ [ ] Edge cases covered │
│ │
└─────────────────────────────────────────────────────────────────────────┘
The Meta-Question
When evaluating any Skill, always return to this fundamental question:
"Would an expert in this domain, looking at this Skill, say:
'Yes, this captures knowledge that took me years to learn'?"
If the answer is yes → the Skill has genuine value.
If the answer is no → it's compressing what Claude already knows.
The best Skills are compressed expert brains — they take a designer's 10 years of aesthetic accumulation and compress it into 43 lines, or a document expert's operational experience into a 200-line decision tree.
What gets compressed must be things Claude doesn't have. Otherwise, it's garbage compression.
Self-Evaluation Note
This Skill (skill-judge) should itself pass evaluation:
- Knowledge Delta: Provides specific evaluation criteria Claude wouldn't generate on its own
- Mindset: Shapes how to think about Skill quality, not just checklist items
- Anti-Patterns: "NEVER Do When Evaluating" section with specific don'ts
- Specification: Valid frontmatter with comprehensive description
- Progressive Disclosure: Self-contained, no external references needed
- Freedom: Medium freedom appropriate for evaluation task
- Pattern: Follows Tool pattern with decision frameworks
- Usability: Clear protocol, report template, quick reference
Evaluate this Skill against itself as a calibration exercise.
