Architecture and Implementation Details

What You'll Learn

• Understand how Agent Skills build toolchain works
• Master the core logic of rule file parsing
• Learn about type system and data flow design
• Study implementation details of framework detection algorithm

Core Architecture Overview

Agent Skills consists of three main parts:

1. Build Toolchain (packages/react-best-practices-build/)

• Parse rule files
• Generate AGENTS.md
• Extract test cases

2. Rule Files (skills/react-best-practices/rules/)

• 57 React performance optimization rules
• Markdown format, following template specifications

3. Deployment Scripts (skills/claude.ai/vercel-deploy-claimable/)

• One-click deployment to Vercel
• Automatic framework detection

Why Understand Architecture?

If you're just using Agent Skills, you might not need deep understanding of these details. But if you need to:

• Develop custom skills
• Write new performance optimization rules
• Troubleshoot build or deployment issues

Understanding the architecture will be very helpful.

Build Pipeline Deep Dive

The build pipeline compiles scattered rule files into AGENTS.md documents readable by AIAgent. The process consists of five stages:

Stage 1: Parse Rule Files (parse)

Each rule file (.md) is parsed into a Rule object through the parseRuleFile() function.

Parsing Order (source location: parser.ts:18-238):

1. Extract Frontmatter (if present)

   • Parse YAML format metadata
   • Supported fields: title, impact, tags, section, explanation, references

2. Extract Title

   • Find the first ## or ### heading
   • If Frontmatter has no title, use the content here

3. Extract Impact

   • Match **Impact:** line
   • Format: **Impact:** CRITICAL (2-10× improvement)
   • Extract level and description

4. Extract Code Examples

   • Find **Label:** markers (such as **Incorrect:**, **Correct:**)
   • Collect subsequent code blocks
   • Capture supplemental text after code block

5. Extract References

   • Find Reference: or References: lines
   • Parse Markdown links [text](url)

6. Infer Section

   • Extract from filename prefix (source location: parser.ts:201-210)
   • Mapping table:
     • async-* → Section 1 (Eliminate Waterfalls)
     • bundle-* → Section 2 (Bundle Optimization)
     • server-* → Section 3 (Server Performance)
     • client-* → Section 4 (Client Side Data Fetching)
     • rerender-* → Section 5 (Re-render Optimization)
     • rendering-* → Section 6 (Rendering Performance)
     • js-* → Section 7 (JavaScript Performance)
     • advanced-* → Section 8 (Advanced Patterns)

Stage 2: Validate Completeness (validate)

Validation logic is implemented in validate.ts, ensuring rule files meet specifications.

Validation Items:

Check Item	Description	Error Output
Title Not Empty	Must have title (Frontmatter or ## heading)	Missing or empty title
At Least One Example	examples array must not be empty	At least one code example required
Impact Valid	Must be a valid ImpactLevel enum value	Invalid impact level
Code Not Empty	Each example must have code content	Empty code block

Stage 3: Group by Section (group)

Group all rules by section, each section contains:

• number: Section number (1-8)
• title: Section title (read from _sections.md)
• impact: Overall impact level
• introduction: Section introduction (optional)
• rules[]: Included rules array

(source location: build.ts:156-169)

Stage 4: Sort by Title (sort)

Rules within each section are sorted alphabetically by title.

Sorting Rule (source location: build.ts:172-175):

section.rules.sort((a, b) =>
  a.title.localeCompare(b.title, 'en-US', { sensitivity: 'base' })
)

Using en-US locale ensures consistent sorting across environments.

Assign IDs (source location: `build.ts:178-180):

section.rules.forEach((rule, index) => {
  rule.id = `${section.number}.${index + 1}`
  rule.subsection = index + 1
})

After sorting, IDs are assigned like 1.1, 1.2...

Stage 5: Generate Document (generate)

The generateMarkdown() function converts the Section[] array into a Markdown document.

Output Structure (source location: build.ts:29-126):

# React Best Practices
**Version 1.0**
Vercel Engineering
January 25, 2026

## Abstract
...

## Table of Contents
1. Eliminate Waterfalls - CRITICAL
   - 1.1 [Parallel Requests](#11-parallel-requests)
   - 1.2 [Defer Await](#12-defer-await)
...

## 1. Eliminate Waterfalls
**Impact: CRITICAL**

### 1.1 Parallel Requests
**Impact: CRITICAL**

**Incorrect:**
```typescript
// code

## Rule Parser Details

### Frontmatter Parsing

Frontmatter is a YAML block at the top of a Markdown file:

```markdown
---
title: Parallel Requests
impact: CRITICAL
impactDescription: 2-10× improvement
tags: async, waterfall
---

Parsing Logic (source location: parser.ts:28-41):

• Detect --- at start and second --- at end
• Split key-value pairs by :
• Remove quote wrapping
• Store in frontmatter object

Code Example Parsing

Each rule contains multiple code examples, marked with **Label:**.

Parsing State Machine (source location: parser.ts:66-188):

Initial State → Read **Label:** → currentExample.label = "Label"
              → Read ``` → inCodeBlock = true, collect code
              → Read ``` → inCodeBlock = false, currentExample.code = collected code
              → Read text → if afterCodeBlock, store in additionalText
              → Read **Reference:** → push currentExample to examples[]

Supported Label Types:

• Incorrect: Incorrect example
• Correct: Correct example
• Example: Generic example
• Usage: Usage example
• Implementation: Implementation example

Supplemental Text Capture (source location: parser.ts:182-186):

// Text after a code block, or text in a section without a code block
// (e.g., "When NOT to use this pattern:" with bullet points instead of code)
else if (currentExample && (afterCodeBlock || !hasCodeBlockForCurrentExample)) {
  additionalText.push(line)
}

This supports adding supplemental text after code blocks, or pure text examples (such as lists).

Reference Parsing

References are at the end of the file, formatted as:

Reference: [React Documentation](https://react.dev), [Next.js Guide](https://nextjs.org/docs)

Parsing Logic (source location: parser.ts:154-174):

• Regex match [text](url) pattern
• Extract all URLs to references[] array

Type System

Type definitions are in types.ts (source location: types.ts:1-54).

ImpactLevel Enum

export type ImpactLevel =
  | 'CRITICAL'
  | 'HIGH'
|---|
  | 'MEDIUM'
|---|
  | 'LOW'

Level Description:

Level	Impact	Example Rule
CRITICAL	Critical bottleneck, must fix	async-parallel
HIGH	Important improvement, recommended priority	server-cache-react
---	---	---
MEDIUM	Medium improvement	rerender-memo
---	---	---
LOW	Incremental improvement, optional	advanced-suspense-boundaries

Rule Interface

export interface Rule {
  id: string                    // Auto-generated, like "1.1"
  title: string                 // Rule title
  section: number              // Section it belongs to (1-8)
  subsection?: number          // Subsection number
  impact: ImpactLevel          // Impact level
  impactDescription?: string  // Impact description, like "2-10× improvement"
  explanation: string          // Rule explanation
  examples: CodeExample[]      // Code example array
  references?: string[]        // Reference links
  tags?: string[]              // Tags
}

CodeExample Interface

export interface CodeExample {
  label: string              // "Incorrect", "Correct", "Example"
  description?: string       // Label description (optional)
  code: string              // Code content
  language?: string         // Code language, default typescript
  additionalText?: string   // Supplemental text after code
}

Section Interface

export interface Section {
  number: number              // Section number (1-8)
  title: string              // Section title
  impact: ImpactLevel        // Overall impact level
  impactDescription?: string // Impact description
  introduction?: string      // Section introduction
  rules: Rule[]             // Included rules
}

GuidelinesDocument Interface

export interface GuidelinesDocument {
  version: string          // Version number, like "1.0"
  organization: string     // Organization name
  date: string            // Date
  abstract: string        // Abstract
  sections: Section[]     // Sections
  references?: string[]   // Global references
}

TestCase Interface

Test cases used for LLM automatic evaluation.

export interface TestCase {
  ruleId: string          // Rule ID, like "1.1"
  ruleTitle: string       // Rule title
  type: 'bad' | 'good'   // Example type
  code: string           // Code content
  language: string       // Code language
  description?: string   // Description
}

Test Case Extraction Mechanism

The test case extraction feature converts code examples from rules into evaluable test cases for LLM automatic assessment of rule compliance.

Extraction Logic (source location: extract-tests.ts:15-38)

function extractTestCases(rule: Rule): TestCase[] {
  const testCases: TestCase[] = []

  rule.examples.forEach((example, index) => {
    const isBad = example.label.toLowerCase().includes('incorrect') ||
                  example.label.toLowerCase().includes('wrong') ||
                  example.label.toLowerCase().includes('bad')
    const isGood = example.label.toLowerCase().includes('correct') ||
                   example.label.toLowerCase().includes('good')

    if (isBad || isGood) {
      testCases.push({
        ruleId: rule.id,
        ruleTitle: rule.title,
        type: isBad ? 'bad' : 'good',
        code: example.code,
        language: example.language || 'typescript',
        description: example.description || `${example.label} example for ${rule.title}`
      })
    }
  })

  return testCases
}

Supported Example Types:

• Incorrect / Wrong / Bad → type = 'bad'
• Correct / Good → type = 'good'

Output File: test-cases.json

Data Structure:

[
  {
    "ruleId": "1.1",
    "ruleTitle": "Parallel Requests",
    "type": "bad",
    "code": "const data = await fetch(url);\nconst result = await process(data);",
    "language": "typescript",
    "description": "Incorrect example for Parallel Requests"
  },
  {
    "ruleId": "1.1",
    "ruleTitle": "Parallel Requests",
    "type": "good",
    "code": "const [data, processed] = await Promise.all([\n  fetch(url),\n  process(data)\n]);",
    "language": "typescript",
    "description": "Correct example for Parallel Requests"
  }
]

Statistics (source location: extract-tests.ts:68-70):

✓ Extracted 120 test cases to test-cases.json
  - Bad examples: 60
  - Good examples: 60

Deployment Script Framework Detection

Vercel deployment script supports automatic detection for 40+ frameworks.

Detection Logic (source location: deploy.sh:12-156)

detect_framework() {
    local pkg_json="$1"
    local content=$(cat "$pkg_json")

    has_dep() {
        echo "$content" | grep -q "\"$1\""
    }

    # Check dependencies, in priority order
    if has_dep "blitz"; then echo "blitzjs"; return; fi
    if has_dep "next"; then echo "nextjs"; return; fi
    if has_dep "gatsby"; then echo "gatsby"; return; fi
    # ... more framework detection
}

Detection Order:

• From specific to general
• Check dependencies and devDependencies
• Use grep -q for quick matching

Supported Frameworks

Category	Framework List	Detection Keywords
React	Next.js, Gatsby, Create React App, Remix, React Router, Blitz	next, gatsby, remix-run
Vue	Nuxt, Vitepress, Vuepress, Gridsome	nuxt, vitepress
Svelte	SvelteKit, Svelte, Sapper	@sveltejs/kit, svelte
Angular	Angular, Ionic Angular	@angular/core
Node.js Backend	Express, Hono, Fastify, NestJS, Elysia, h3, Nitro	express, hono, nestjs
Build Tools	Vite, Parcel	vite, parcel
Static HTML	No package.json	Returns null

Static HTML Project Handling (source location: deploy.sh:192-206)

Static HTML projects (no package.json) need special handling:

if [ ! -f "$PROJECT_PATH/package.json" ]; then
  # Find HTML files in root directory
  HTML_FILES=$(find "$PROJECT_PATH" -maxdepth 1 -name "*.html" -type f)
  HTML_COUNT=$(echo "$HTML_FILES" | grep -c . || echo 0)

  # If only one HTML file and not index.html, rename to index.html
  if [ "$HTML_COUNT" -eq 1 ]; then
    HTML_FILE=$(echo "$HTML_FILES" | head -1)
    BASENAME=$(basename "$HTML_FILE")
    if [ "$BASENAME" != "index.html" ]; then
      echo "Renaming $BASENAME to index.html..." >&2
      mv "$HTML_FILE" "$PROJECT_PATH/index.html"
    fi
  fi
fi

Why Rename? Vercel defaults to looking for index.html as the entry file for static sites.

Deployment Flow (source location: deploy.sh:158-249)

# 1. Parse arguments
INPUT_PATH="${1:-.}"

# 2. Create temporary directory
TEMP_DIR=$(mktemp -d)

# 3. Detect framework
FRAMEWORK=$(detect_framework "$PROJECT_PATH/package.json")

# 4. Create tarball (excluding node_modules and .git)
tar -czf "$TARBALL" -C "$PROJECT_PATH" --exclude='node_modules' --exclude='.git' .

# 5. Upload to API
RESPONSE=$(curl -s -X POST "$DEPLOY_ENDPOINT" -F "file=@$TARBALL" -F "framework=$FRAMEWORK")

# 6. Parse response
PREVIEW_URL=$(echo "$RESPONSE" | grep -o '"previewUrl":"[^"]*"' | cut -d'"' -f4)
CLAIM_URL=$(echo "$RESPONSE" | grep -o '"claimUrl":"[^"]*"' | cut -d'"' -f4)

# 7. Output result
echo "Preview URL: $PREVIEW_URL"
echo "Claim URL:   $CLAIM_URL"
echo "$RESPONSE"  # JSON format for program use

Error Handling (source location: deploy.sh:224-239):

if echo "$RESPONSE" | grep -q '"error"'; then
  ERROR_MSG=$(echo "$RESPONSE" | grep -o '"error":"[^"]*"' | cut -d'"' -f4)
  echo "Error: $ERROR_MSG" >&2
  exit 1
fi

if [ -z "$PREVIEW_URL" ]; then
  echo "Error: Could not extract preview URL from response" >&2
  exit 1
fi

Next Steps

After understanding the architecture, you can:

• Develop Custom Skills
• Write React Best Practices Rules
• View API and Command Reference

Appendix: Source Code Reference

Click to expand source code locations

Last updated: 2026-01-25

Feature	File Path	Line Numbers
Type System	packages/react-best-practices-build/src/types.ts	1-54
Path Configuration	packages/react-best-practices-build/src/config.ts	1-18
Rule Parser	packages/react-best-practices-build/src/parser.ts	18-238
Build Script	packages/react-best-practices-build/src/build.ts	131-287
Test Case Extraction	packages/react-best-practices-build/src/extract-tests.ts	15-38
Deployment Script Framework Detection	skills/claude.ai/vercel-deploy-claimable/scripts/deploy.sh	12-156

Key Constants:

• ImpactLevel enum values: CRITICAL, HIGH, MEDIUM-HIGH, MEDIUM, LOW-MEDIUM, LOW (types.ts:5)
• SKILL_DIR: Skill directory path (config.ts:11)
• RULES_DIR: Rules files directory (config.ts:13)
• DEPLOY_ENDPOINT: https://claude-skills-deploy.vercel.com/api/deploy (deploy.sh:9)

Key Functions:

• parseRuleFile(): Parse Markdown rule file into Rule object (parser.ts:18)
• extractTestCases(): Extract test cases from rules (extract-tests.ts:15)
• generateMarkdown(): Generate Markdown document from Section[] (build.ts:29)
• detect_framework(): Detect project framework (deploy.sh:12)