blueprint-derive-rules

---
name: blueprint-derive-rules
description: Derive Claude rules from git commit history. Use when extracting implicit decisions from commits or codifying code-style, testing, and API-design rules.
license: MIT
---

# /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/`):

```bash
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](REFERENCE.md#git-analysis)):

- **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](REFERENCE.md#rule-template). 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](REFERENCE.md#rule-categories) 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`:

```bash
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 |

---

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