blueprint-derive-rules

/blueprint:derive-rules

Extract project decisions from git commit history and codify them as Claude rules. Newer commits override older decisions when conflicts exist.

Use case: Derive implicit project patterns from git history to establish consistent AI-assisted development guidelines.

Usage: /blueprint:derive-rules [--since DATE] [--scope SCOPE]

When to Use This Skill

Use this skill when...	Use alternative when...
Want to extract implicit decisions from git history	Creating rules from requirements (use PRDs instead)
Project has significant commit history	New project with little history
Establishing project coding standards	Quick manual rule creation

Context

• Git repository: !git rev-parse --git-dir
• Blueprint initialized: !find . -path '*/docs/blueprint/*' -maxdepth 3 -name 'manifest.json' -type f
• Total commits: !git rev-list --count HEAD
• Conventional commits %: !git log --format="%s"
• Existing rules in default location: !find . -path '*/.claude/rules/*' -maxdepth 3 -name "*.md" -type f
• Existing rules in blueprint subdir: !find . -path '*/.claude/rules/blueprint/*' -maxdepth 4 -name "*.md" -type f

Parameters

Parse $ARGUMENTS:

• --since DATE: Analyze commits from specific date (e.g., --since 2024-01-01)
• --scope SCOPE: Focus on specific area (e.g., --scope api, --scope testing)

Execution

Execute the complete git-to-rules derivation workflow:

Step 0: Resolve the output path

Read structure.generated_rules_path from docs/blueprint/manifest.json (default .claude/rules/):

RULES_DIR=$(jq -r '.structure.generated_rules_path // ".claude/rules/"' docs/blueprint/manifest.json)
mkdir -p "$RULES_DIR"

Use $RULES_DIR for all subsequent reads/writes and conflict checks. Hand-written files in the parent .claude/rules/ are intentionally invisible to this skill (issue #1043).

Step 1: Verify prerequisites

1. If not a git repository → Error: "This directory is not a git repository"
2. If Blueprint not initialized → Suggest /blueprint:init first
3. If few commits (< 20) → Warn: "Limited commit history; derived rules may be incomplete"

Step 2: Analyze git history quality

1. Calculate total commits in scope
2. Calculate conventional commits percentage
3. Report quality: Higher % = higher confidence in extracted rules
4. Parse --since and --scope flags to determine analysis range

Step 3: Extract decision-bearing commits

Use parallel agents to analyze git history efficiently (see REFERENCE.md):

• Agent 1: Analyze refactor: commits for code style patterns
• Agent 2: Analyze fix: commits for repeated issue types
• Agent 3: Analyze feat!: and BREAKING CHANGE: commits for architecture decisions
• Agent 4: Analyze chore: and build: commits for tooling decisions

Consolidate findings by domain (code-style, testing, api-design, etc.), chronologically (newest first), and by frequency (most common wins).

Step 4: Resolve conflicts

When multiple commits address the same topic:

1. Detect conflicts using pattern matching: git log --format="%H|%ai|%s" | grep "{topic}"
2. Apply resolution strategy:
   • Newer overrides older: Latest decision wins
   • Higher frequency wins: If 5 commits say X and 1 says Y, X wins
   • Breaking changes override: feat!: trumps regular commits
3. Mark overridden decisions as "superseded" with reference to newer decision
4. Confirm significant decisions with user via AskUserQuestion

Step 5: Generate rules in $RULES_DIR

For each decision, generate rule file using template from REFERENCE.md. Write each file to $RULES_DIR/<filename>.md (the configured structure.generated_rules_path):

1. Extract source commit, date, type

2. Determine confidence level (High/Medium/Low based on commit frequency and clarity)

3. Generate actionable rule statement

4. Include code examples from commit diffs

5. Reference any superseded earlier decisions

6. REQUIRED: scope every generated rule via paths: frontmatter unless the rule genuinely applies everywhere. Rules without paths: load on every session and pollute context for unrelated work. Pick paths: from the source signal:

   Signal	Source	paths: value
   Rule body cites a specific file via "patterns extracted from <path>"	Step 3 / 4 conflict resolution	Glob over that file's directory: <dir>/**/*.<ext>
   Rule was derived from chore(deps) / build: commits	Tooling-decision agent	Lockfiles + manifests: package.json, pyproject.toml, Cargo.toml, go.mod, *.lock, biome.json, etc.
   Rule references a language (refactor: + JS-only code blocks)	Code-style agent	Language Glob: **/*.{js,jsx,ts,tsx}, **/*.py, **/*.rs
   Rule is about tests	Test-strategy agent	**/*.{test,spec}.*, tests/**/*, test/**/*
   Rule is about API endpoints	API-design agent	src/{api,routes}/**/*, **/*controller*, **/*handler*
   Rule is about documentation	Docs agent	docs/**, **/*.md
   Rule restates global project context (already in CLAUDE.md)	any	Do not emit — that's CLAUDE.md's job; abort the rule
   Rule genuinely applies to every file (e.g. universal error-handling philosophy, security mindset)	Rare	Omit paths: deliberately and note "global rule" in the rule body

   Default to scoping. The auto-derived starting point: take every code block in the rule body, collect the file extensions / directory roots they reference, and emit those as paths:. Verify the resulting glob set actually matches files in the working tree before writing — an empty match list means the inferred scope is wrong; re-derive.

Generate separate rule files by category (see REFERENCE.md for canonical filenames and default paths: per category):

• code-style.md, testing-standards.md, api-conventions.md, error-handling.md, dependencies.md, security-practices.md

Step 6: Handle conflicts with existing rules

Check for conflicts with existing rules only under $RULES_DIR (never the parent .claude/rules/, which may contain hand-authored content unrelated to blueprint):

1. If conflicts found → Ask user: Git-derived overrides existing rule, or keep existing?
2. Apply user choice: Update, merge, or keep separate
3. Document conflict resolution in rule file

Step 7: Update task registry

Update the task registry entry in docs/blueprint/manifest.json:

jq --arg now "$(date -u +%Y-%m-%dT%H:%M:%SZ)" \
  --arg sha "$(git rev-parse HEAD 2>/dev/null)" \
  --argjson processed "${COMMITS_ANALYZED:-0}" \
  --argjson created "${RULES_DERIVED:-0}" \
  '.task_registry["derive-rules"].last_completed_at = $now |
   .task_registry["derive-rules"].last_result = "success" |
   .task_registry["derive-rules"].context.commits_analyzed_up_to = $sha |
   .task_registry["derive-rules"].stats.runs_total = ((.task_registry["derive-rules"].stats.runs_total // 0) + 1) |
   .task_registry["derive-rules"].stats.items_processed = $processed |
   .task_registry["derive-rules"].stats.items_created = $created' \
  docs/blueprint/manifest.json > tmp.json && mv tmp.json docs/blueprint/manifest.json

Step 8: Update manifest and report

1. Update docs/blueprint/manifest.json with derived rules metadata: timestamp, commits analyzed, rules generated, source commits
2. Generate completion report showing:
   • Commits analyzed (count and date range)
   • Conventional commits percentage
   • Rules generated by category
   • Confidence scores per rule
   • Any conflicts resolved
3. Prompt user for next action: Review rules, execute derived development workflow, or done

Agentic Optimizations

Context	Command
Check git status	git rev-parse --git-dir 2>/dev/null && echo "YES" || echo "NO"
Count total commits	git rev-list --count HEAD 2>/dev/null || echo "0"
Conventional commits %	git log --format="%s" | grep -c "^(feat|fix|refactor)" || echo 0
Extract decision commits	git log --format="%H|%s|%b" | grep -E "(always|never|must|prefer)"
Fast derivation	Use parallel agents (Explore) for multi-domain analysis

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For git analysis patterns, rule templates, conflict resolution, and detailed procedures, see REFERENCE.md.