Monorepo Navigator

---
name: "monorepo-navigator"
description: "Multiple packages/apps share code (UI components, utils, types, API clients)"
executor: HYBRID
skill_id: engineering.cs-engineering.monorepo-navigator
status: ADOPTED
security: {level: standard, pii: false, approval_required: false}
anchors:
  - engineering
tier: 2
input_schema:
  - name: code_or_task
    type: string
    description: "Code snippet, script, or task description to process"
    required: true
output_schema:
  - name: result
    type: string
    description: "Primary output from monorepo navigator"
---

# Monorepo Navigator

**Tier:** POWERFUL  
**Category:** Engineering  
**Domain:** Monorepo Architecture / Build Systems  

---

## Overview

Navigate, manage, and optimize monorepos. Covers Turborepo, Nx, pnpm workspaces, and Lerna. Enables cross-package impact analysis, selective builds/tests on affected packages only, remote caching, dependency graph visualization, and structured migrations from multi-repo to monorepo. Includes Claude Code configuration for workspace-aware development.

---

## Core Capabilities

- **Cross-package impact analysis** — determine which apps break when a shared package changes
- **Selective commands** — run tests/builds only for affected packages (not everything)
- **Dependency graph** — visualize package relationships as Mermaid diagrams
- **Build optimization** — remote caching, incremental builds, parallel execution
- **Migration** — step-by-step multi-repo → monorepo with zero history loss
- **Publishing** — changesets for versioning, pre-release channels, npm publish workflows
- **Claude Code config** — workspace-aware CLAUDE.md with per-package instructions

---

## When to Use

Use when:
- Multiple packages/apps share code (UI components, utils, types, API clients)
- Build times are slow because everything rebuilds when anything changes
- Migrating from multiple repos to a single repo
- Need to publish packages to npm with coordinated versioning
- Teams work across multiple packages and need unified tooling

Skip when:
- Single-app project with no shared packages
- Team/project boundaries are completely isolated (polyrepo is fine)
- Shared code is minimal and copy-paste overhead is acceptable

---

## Tool Selection

| Tool | Best For | Key Feature |
|---|---|---|
| **Turborepo** | JS/TS monorepos, simple pipeline config | Best-in-class remote caching, minimal config |
| **Nx** | Large enterprises, plugin ecosystem | Project graph, code generation, affected commands |
| **pnpm workspaces** | Workspace protocol, disk efficiency | `workspace:*` for local package refs |
| **Lerna** | npm publishing, versioning | Batch publishing, conventional commits |
| **Changesets** | Modern versioning (preferred over Lerna) | Changelog generation, pre-release channels |

Most modern setups: **pnpm workspaces + Turborepo + Changesets**

---

## Turborepo
→ See references/monorepo-tooling-reference.md for details

## Workspace Analyzer

```bash
python3 scripts/monorepo_analyzer.py /path/to/monorepo
python3 scripts/monorepo_analyzer.py /path/to/monorepo --json
```

Also see `references/monorepo-patterns.md` for common architecture and CI patterns.

## Common Pitfalls

| Pitfall | Fix |
|---|---|
| Running `turbo run build` without `--filter` on every PR | Always use `--filter=...[origin/main]` in CI |
| `workspace:*` refs cause publish failures | Use `pnpm changeset publish` — it replaces `workspace:*` with real versions automatically |
| All packages rebuild when unrelated file changes | Tune `inputs` in turbo.json to exclude docs, config files from cache keys |
| Shared tsconfig causes one package to break all type-checks | Use `extends` properly — each package extends root but overrides `rootDir` / `outDir` |
| git history lost during migration | Use `git filter-repo --to-subdirectory-filter` before merging — never move files manually |
| Remote cache not working in CI | Check TURBO_TOKEN and TURBO_TEAM env vars; verify with `turbo run build --summarize` |
| CLAUDE.md too generic — Claude modifies wrong package | Add explicit "When working on X, only touch files in apps/X" rules per package CLAUDE.md |

---

## Best Practices

1. **Root CLAUDE.md defines the map** — document every package, its purpose, and dependency rules
2. **Per-package CLAUDE.md defines the rules** — what's allowed, what's forbidden, testing commands
3. **Always scope commands with --filter** — running everything on every change defeats the purpose
4. **Remote cache is not optional** — without it, monorepo CI is slower than multi-repo CI
5. **Changesets over manual versioning** — never hand-edit package.json versions in a monorepo
6. **Shared configs in root, extended in packages** — tsconfig.base.json, .eslintrc.base.js, jest.base.config.js
7. **Impact analysis before merging shared package changes** — run affected check, communicate blast radius
8. **Keep packages/types as pure TypeScript** — no runtime code, no dependencies, fast to build and type-check

---

## Why This Skill Exists

Implement — Monorepo Navigator

<!-- SR_40: auto-generated from frontmatter `purpose`/`description` (OPP-Phase3). Expand with domain-specific rationale. -->

## What If Fails

If this skill fails to produce the expected output: (1) verify input completeness, (2) retry with more specific context, (3) fall back to the parent workflow without this skill.

<!-- SR_40: auto-generated from frontmatter `what_if_fails` (OPP-Phase3). -->