Extract Rules

Analyzes existing codebase to identify what Claude would get wrong without project-specific guidance, extracting coding rules and domain knowledge as structured markdown documentation for AI agents.

Usage

/extract-rules                      # Extract rules from codebase (initial)
/extract-rules --update             # Re-scan and add new patterns (preserve existing)
/extract-rules --restructure        # Re-analyze, reorganize structure, merge existing rules
/extract-rules --from-conversation              # Extract from current session (latest)
/extract-rules --from-conversation <session-id> # Extract from a specific session
/extract-rules --from-pr 123                   # PR in current repo
/extract-rules --from-pr owner/repo#123        # PR in another repo (URL form also accepted)
/extract-rules --from-pr 100..110              # PR range (current repo)
/extract-rules --from-pr owner/repo#100..110   # PR range (another repo)
/extract-rules --compact                       # Compact all over-threshold rules files (output_dir/**/*.md)
/extract-rules --compact path/to/file.md ...   # Compact specific files (caller passes explicit paths)
/extract-rules --realign                       # Re-judge every rule file under output_dir against current criteria
/extract-rules --realign path/to/file.md ...   # Re-judge only the named files
/extract-rules --apply-conversation-candidates <path>  # Apply pre-scanned rule candidates (Step C5 only; orchestrator sub-skill)
# Multiple specs allowed (space-separated) → cross-analysis detects org-wide principles

Change-origin flags: a change-based extraction is scoped only by --from-conversation or --from-pr. This skill accepts no diff-base / commit-sha origin argument such as --base-commit <sha>; passing one is unsupported.

Configuration

Settings file: extract-rules.local.md (YAML frontmatter only, no markdown body)

• Project-level: .claude/extract-rules.local.md (takes precedence)
• User-level: ~/.claude/extract-rules.local.md

Setting	Default	Description
target_dirs	["."]	Analysis target directories
exclude_dirs	[".git", ".claude"]	Exclude directories (in addition to .gitignore)
exclude_patterns	[]	Exclude file patterns (e.g., *.generated.ts, *.d.ts)
output_dir	.claude/rules	Output directory for rule files (.md and .local.md)
examples_output_dir	.claude/rules-extras	Output directory for .examples.md files. Defaults to a sibling directory outside .claude/rules/** so examples are not auto-loaded into context on session start. Set to output_dir (or any path under output_dir) to opt examples back into auto-load
staging_output_dir	.claude/rules-staging	Output directory for 1st-observation project-level patterns staged by incremental modes. Defaults to a sibling directory outside .claude/rules/** so staged candidates are not auto-loaded into context on session start. Set to output_dir (or any path under output_dir) to opt staging back into auto-load. Staging gating and the promote path: references/conversation-mode.md § Step C5 and § Mode interaction summary
language	ja	Report language (e.g., ja)
split_output	true	Separate Principles (.md) and patterns (.local.md)
resolve_references	true	Resolve file references during restructure
compaction_threshold	40000	Char count threshold for --compact mode (file is compacted if char count exceeds this). Set to a very large number (e.g. 99999999) to opt out of compaction. The default 40000 matches Claude Code's per-file warning threshold (40k chars, observed in Claude Code 2.1.x) — firing the gate exactly at the warning matches the user's visible signal that the file needs attention (buffer 0).
min_cluster_size	3	Minimum related-bullet cluster size for --compact mode's consolidation detection. The subagent emits consolidation_proposals only when a cluster has at least this many related bullets. Set to a very large number (e.g. 99999999) to disable consolidation while keeping compaction

---
target_dirs:
  - .
exclude_dirs:
  - .git
  - .claude
exclude_patterns:
  - "*.generated.ts"
output_dir: .claude/rules
examples_output_dir: .claude/rules-extras
staging_output_dir: .claude/rules-staging
language: ja
split_output: true
resolve_references: true
compaction_threshold: 40000
min_cluster_size: 3
---

Output Structure

Three output directories are involved: output_dir for rule files (.md / .local.md), examples_output_dir for .examples.md files, and staging_output_dir for staged 1st-observation project-level patterns from incremental modes. The paths: frontmatter on rule files is a human-facing category-scope hint; the auto-load boundary is determined by directory placement only.

Default (split_output: true):

.claude/rules/                     # output_dir (inside auto-load scope)
├── languages/
│   ├── typescript.md              # Principles only (portable)
│   └── typescript.local.md        # Project-specific patterns only
├── frameworks/
│   ├── react.md                   # Principles only (portable)
│   └── react.local.md             # Project-specific patterns only
└── project.md                     # Always single file (no split)

.claude/rules-extras/              # examples_output_dir (outside auto-load scope)
├── languages/
│   └── typescript.examples.md     # Examples for both
├── frameworks/
│   └── react.examples.md          # Examples for both
└── project.examples.md            # Examples

.claude/rules-staging/             # staging_output_dir (outside auto-load scope)
└── project.staging.local.md       # 1st-observation project-level candidates (incremental modes only)

Principles (portable across projects) and Project-specific patterns (local) are separated by default.

Hybrid mode (split_output: false): no <name>.local.md — each <name>.md carries both ## Principles and ## Project-specific patterns. The other two directories are unchanged.

Layered frameworks (Rails, Django, Spring, etc.): When a framework has distinct architectural layers, generate layer-specific files:

• <framework>.md — Cross-layer rules (no paths: or broad scope)
• <framework>-<layer>.md — Layer-specific rules with scoped paths: (e.g., app/models/**)
• In split mode, both cross-layer and layer-specific files get .local.md counterparts

Integration libraries (Inertia, Pundit, Devise, Turbo, etc.): When integration libraries are detected alongside a layered framework:

• integrations/<framework>-<integration>.md — Integration-specific rules
• Separated from layer files into dedicated integrations/ directory
• In split mode, integration files also get .local.md counterparts

Format switching: Run --restructure after changing split_output setting to switch between split and hybrid formats.

Dispatch authorization

This skill's procedure dispatches subagents, so invoking the skill is the request to use that mechanism: an ambient instruction allowing subagent dispatch only when the user asked for it — a permission-shaped restriction — is already satisfied by this invocation. Do not ask the user to re-confirm the dispatch, and do not silently substitute inline execution for a dispatch this procedure specifies. Only two things justify that substitution: technical availability (the dispatch tool is not present and callable on the current tool surface), and an explicit contract term from the caller bounding this skill to its own thread. A permission-shaped restriction is neither.

Processing Flow

Mode Detection

Check arguments to determine mode:

• No arguments → Full Extraction Mode (Step 1-7)
• --update → Update Mode (Step U1-U6)
• --restructure → Restructure Mode (Step R1-R5)
• --from-conversation [session-id] → Conversation Extraction Mode (Step C1-C5)
• --compact [<paths>] → Compaction Mode (Step CP1-CP5)
• --realign [<paths>] → Realign Mode (Step RA1-RA5)
• --from-pr <number|owner/repo#number|range> [...] → PR Review Extraction Mode (Step P1-P5)
• --apply-conversation-candidates <path> → Conversation Candidate Apply Mode (Step A1-A2)

---

Full Extraction Mode

Step 1: Load Settings

Search for extract-rules.local.md:

1. Project-level: .claude/extract-rules.local.md
2. User-level: ~/.claude/extract-rules.local.md

Priority:

• If both exist, use project-level only
• If only one exists, use that file
• If neither exists, use default settings

Extract settings (target_dirs, exclude_dirs, exclude_patterns, output_dir, examples_output_dir, staging_output_dir, language, split_output, resolve_references, compaction_threshold) from the config file. See Configuration section above for defaults.

language resolution: skill config → Claude Code settings (~/.claude/settings.json language field) → default ja. Write the report's prose in plain words, one claim per sentence, with no figure of speech translated word for word.

Load existing rule files (incremental modes; Full Extraction skips it): read <output_dir>/<name>.md, <output_dir>/<name>.local.md, and <examples_output_dir>/<name>.examples.md. When examples_output_dir does not exist yet (legacy projects that co-located examples under output_dir), use <output_dir>/<name>.examples.md instead. Also read <staging_output_dir>/project.staging.local.md when present — the staging-match branch needs it; skip silently when it does not exist.

Step 2: Detect Project Type

Detect project language and framework:

1. Detect languages by config files (package.json, tsconfig.json, pyproject.toml, go.mod, Cargo.toml, Gemfile, pom.xml, etc.) and file extensions (.ts/.tsx, .py, .go, .rb, etc.)

2. Detect frameworks by their config files (e.g., next.config.*, playwright.config.*) and dependencies in package manifests.

3. Detect architectural layers (for layered frameworks): If a framework has distinct layers with separate directories (e.g., Rails: app/models/, app/controllers/; Django: models.py, views.py), detect them for layer-specific rule files. Only split when corresponding directories actually exist.

4. Detect integration libraries (for layered frameworks): Read references/integration-criteria.md for detection rules and classification criteria.

Output: List of detected languages, frameworks, architectural layers, and integration libraries

Step 3: Collect Sample Files

Collect target files for analysis:

1. Get git-tracked files using git ls-files (respects .gitignore). If not a git repo, use Glob instead, with manual exclusions from settings.
2. Filter by target_dirs, exclude_dirs, exclude_patterns, and detected language extensions
3. Sample 10-15 files per category, distributed across directories for representative coverage. Large projects (100+): prioritize directory diversity. Small projects (<10): analyze all files.

Step 4: Analyze by Category

Read references/extraction-criteria.md before proceeding to understand the classification criteria. The core question for every pattern is: "Would Claude produce something different without knowing this?" — extract only what fills the gap between Claude's general knowledge and this project's actual conventions.

For each detected language, framework, and integration library:

1. Use Grep/Read to collect relevant code patterns

1.5. Separate integration-specific patterns (for layered frameworks with integrations): See references/integration-criteria.md "Pattern routing" section.

2. Classify each pattern (see references/extraction-criteria.md):

   • General style choice (uses only language built-ins) → Abstract principle + hints
   • Project-defined symbol (types, functions, hooks defined in project) → Include concrete example

3. For general style patterns:

   • Group related patterns (e.g., "prefer const", "avoid mutations", "use spread" → Immutability)
   • Formulate as principle with parenthetical implementation hints (2-4 keywords)

4. For project-specific patterns:

   • Extract only the minimal signature (type definition, function signature, or API combination)
   • Format as one line: signature - brief context (2-5 words)
   • Avoid multi-line code blocks

5. Apply AI judgment to determine which patterns meet the extraction criteria (see references/extraction-criteria.md)

Determine appropriate detection methods based on language and project structure.

Step 5: Analyze Documentation and Existing Rules

Also analyze non-code documentation:

• README.md
• CONTRIBUTING.md
• PR templates
• Existing CLAUDE.md

Extract explicit coding rules and guidelines from these documents.

Deduplication check: Read any files under .claude/rules/ to build a set of already-documented rules. Rules extracted in Step 4 that overlap with these existing rules should be skipped. Note: CLAUDE.md is NOT a deduplication source — rules should exist in .claude/rules/ even if also mentioned in CLAUDE.md. This check applies to every mode that extracts new rules.

Step 6: Generate Output

Read references/security.md before generating output to ensure sensitive information is not included.

1. Check if output_dir exists

   • If exists: Error "Output directory already exists. Use --restructure to reorganize, --update to add new patterns, or delete the directory manually to start fresh."
   • If not exists: Create output_dir. Also create examples_output_dir if it differs from output_dir and does not exist yet (when both resolve to the same path the single directory created above is reused).

2. Generate rule files per category. Rule files (<name>.md and <name>.local.md) are written under output_dir; <name>.examples.md files are written under examples_output_dir.

   • languages/<lang>.md for language-specific rules (under output_dir)
   • frameworks/<framework>.md for framework-specific rules (under output_dir)
   • project.md for project-specific rules (under output_dir)
   • Layered frameworks: <framework>.md (cross-layer) + <framework>-<layer>.md per detected layer with scoped paths:
   • Integration libraries: See references/integration-criteria.md "Output structure" section.

   By default (split_output: true): Generate 3 files per category (except project which gets 2):

   • <output_dir>/<name>.md — ## Principles only (portable), with paths: frontmatter
   • <output_dir>/<name>.local.md — ## Project-specific patterns only (local), with the same paths: frontmatter as its <name>.md counterpart
   • <examples_output_dir>/<name>.examples.md — Examples for both
   • Layer-specific and regular files each define their own paths: independently (applies to both .md and .local.md). Cross-layer files (<framework>.md / <framework>.local.md) use no paths: or broad scope.
   • Skip generating a file if it would be empty. Skipped files are omitted from the Step 7 report.

   When split_output: false: Generate single hybrid file per category under output_dir, and the matching <name>.examples.md under examples_output_dir.

Rule file format (hybrid example):

---
paths:
  - "**/*.ts"
  - "**/*.tsx"
---
# TypeScript Rules

## Principles

- FP only (no classes, pure functions, composition over inheritance)
- Strict null handling (no non-null assertions, explicit narrowing required)
- Barrel exports required (re-export from index.ts per directory)

## Project-specific patterns

- `RefOrNull<T extends { id: string }> = T | { id: null }` - nullable relationships
- `pathFor(page) + url()` - Page Object navigation pair
- `useAuthClient()` returns `{ user, login, logout }` - auth hook interface

## Examples

When in doubt: ../../rules-extras/languages/typescript.examples.md

(The path above assumes default settings — output_dir: .claude/rules and examples_output_dir: .claude/rules-extras. See references/examples-format.md § Reference Section in Rule Files for the relative-path computation under non-default settings.)

Format guidelines:

For Principles section:

• Each principle: Principle name (hint1, hint2, hint3)
• Principle name: noun phrase naming the philosophy (e.g., "Immutability" not "Use const")
• Hints: 2-4 keywords per principle, describing implementation techniques observed in the project
• Only for general style choices (language built-ins)

For Project-specific patterns section:

• One line per pattern: `signature` - brief context
• Use inline code for signatures, not code blocks
• Keep context to 2-5 words
• Only include the minimal signature: type name, function signature with return type, or API combination
• Example of minimal: useAuth() → { user, login, logout } (not full implementation)

For a prose rule — a project-level rule stating a working convention rather than naming a symbol — see references/extraction-criteria.md § What a Rule Is Made Of.

For .examples.md files: Read references/examples-format.md for file structure, Good/Bad contrast guidelines, and the reference section format. Each rule file with a corresponding .examples.md must end with a ## Examples reference section (see the reference for format). ### titles must match the corresponding rule name exactly — do not translate or rephrase.

paths patterns by category:

• TypeScript: **/*.ts, **/*.tsx
• Python: **/*.py
• React: **/*.tsx, **/*.jsx
• Integration libraries: scope paths: to layers where the integration is used (e.g., Inertia in controllers: app/controllers/**)
• (project.md: no paths frontmatter = applies to all files)

Step 6.5: Security Self-Check

After generating all rule files, verify no sensitive information was included:

1. Grep generated/updated files for patterns that may indicate secrets:
   • Long hex strings: [0-9a-fA-F]{20,}
   • Base64-like strings: [A-Za-z0-9+/=]{40,}
   • Keyword-adjacent literals: (key|token|secret|password|credential)\s*[:=]\s*["'][^"']+
   • Internal URLs: (internal|staging|localhost:[0-9]+)
2. If found, redact with placeholders (e.g., API_KEY_REDACTED) and warn the user

Note: This check applies to all modes that write rule files. Also check .examples.md files.

Step 7: Report Summary

Display analysis summary. See references/report-templates.md § Full Extraction Mode (Step 7) for format.

---

Update Mode

When --update is specified, re-scan the codebase and add new patterns while preserving existing rules. Update Mode reads the staging file and promotes re-matched project-level patterns to canonical; it never writes new staging entries.

Read references/update-mode.md for the full processing steps (U1-U6); re-read it when a Step U reference no longer resolves in context. Key flow:

1. Load settings; check prerequisites and load existing rule files
2. Re-scan the codebase (Step 2-5 of Full Extraction Mode)
3. Staleness check on existing project-specific patterns
4. Compare, merge, and append new rules; promote staging matches
5. Security Self-Check
6. Audit Pass over what was written, then report

---

Restructure Mode

When --restructure is specified, re-analyze the codebase to determine the optimal file structure, then merge existing rule content into the new structure. Use this when the project has evolved (new frameworks, architectural changes) or when split_output settings change; README.md § Choosing a mode says which mode a given change calls for.

Read references/restructure-mode.md for the full processing steps (R1-R5); re-read it when a Step R reference no longer resolves in context. Key flow:

1. Load settings; snapshot the existing rule files
2. Re-analyze the codebase (Step 2-5 of Full Extraction Mode)
3. Resolve file references in the snapshot (skipped when resolve_references: false)
4. USER CONFIRMATION on the restructure plan, then merge and write
5. Security Self-Check, then report

---

Conversation Extraction Mode

When --from-conversation is specified, extract rules from the full conversation history stored in session .jsonl files. The heavy processing (jsonl parsing, analysis, rule writing) is delegated to a subagent.

Step C1: Prepare and Locate Session File (main agent)

1. Load settings from extract-rules.local.md (same as Step 1 in Full Extraction Mode)

2. Check if output directory exists (default: .claude/rules/)

   • If not exists: Error "Run /extract-rules first to initialize rule files."

3. Locate the session file:

   1. Get the current working directory (pwd)
   2. Encode the path: replace / and . with - (leading - is kept)
      • Example: /Users/alice/src/github.com/acme/widget → -Users-alice-src-github-com-acme-widget
   3. Session files are stored at: ~/.claude/projects/<encoded-path>/<session-id>.jsonl

4. Select the target session:

   • If a <session-id> argument is provided: use ~/.claude/projects/<encoded-path>/<session-id>.jsonl
   • If no argument: use the most recently modified .jsonl file in the directory (by ls -t)
     • Note: This is a heuristic — if multiple Claude Code instances are running concurrently, the latest file may not be the current session.
   • Verify the file exists. Inform the user which session file was selected.

Step C2: Delegate to Subagent (main agent)

Spawn a subagent using the Agent tool. The subagent performs all heavy processing (C3–C5) and returns a summary of what was added. Read references/conversation-mode.md for the full subagent instructions (Steps C3–C5).

Include in the agent prompt:

• This skill's absolute directory path (where SKILL.md resides — needed to run bundled scripts)
• Session file absolute path
• output_dir, examples_output_dir, and staging_output_dir paths, plus split_output / language settings (the subagent must write rule files under output_dir, .examples.md files under examples_output_dir, and staging entries under staging_output_dir)
• canonical_files: list of existing rule file paths for canonical-match deduplication — include both rule files under output_dir and .examples.md files under examples_output_dir
• staging_files: list of existing staging file paths for staging-match detection — include the project-level staging file under staging_output_dir (gating is scoped to project-level patterns)
• The subagent instructions from references/conversation-mode.md

After the subagent completes, run the Audit Pass over the write record it returned, then report the results to the user.

---

Conversation Candidate Apply Mode

When --apply-conversation-candidates <path> is specified, run only Step C5 (dedup / route / write / promote / .examples.md / Security Self-Check) against a pre-scanned rule-candidate block, skipping the jsonl parsing and analysis (C3/C4).

The input candidate file conforms to references/conversation-mode.md § Rule-candidate contract. This mode runs entirely in the main agent (no subagent spawn).

Step A1: Load Settings and Read Candidates (main agent)