Lightfastai Lightfast Turborepo

Turborepo Skill

Build system for JavaScript/TypeScript monorepos. Turborepo caches task outputs and runs tasks in parallel based on dependency graph.

IMPORTANT: Package Tasks, Not Root Tasks

DO NOT create Root Tasks. ALWAYS create package tasks.

When creating tasks/scripts/pipelines, you MUST:

1. Add the script to each relevant package's package.json
2. Register the task in root turbo.json
3. Root package.json only delegates via turbo run <task>

DO NOT put task logic in root package.json. This defeats Turborepo's parallelization.

// DO THIS: Scripts in each package
// apps/web/package.json
{ "scripts": { "build": "next build", "lint": "eslint .", "test": "vitest" } }

// apps/api/package.json
{ "scripts": { "build": "tsc", "lint": "eslint .", "test": "vitest" } }

// packages/ui/package.json
{ "scripts": { "build": "tsc", "lint": "eslint .", "test": "vitest" } }

// turbo.json - register tasks
{
  "tasks": {
    "build": { "dependsOn": ["^build"], "outputs": ["dist/**"] },
    "lint": {},
    "test": { "dependsOn": ["build"] }
  }
}

// Root package.json - ONLY delegates, no task logic
{
  "scripts": {
    "build": "turbo run build",
    "lint": "turbo run lint",
    "test": "turbo run test"
  }
}

// DO NOT DO THIS - defeats parallelization
// Root package.json
{
  "scripts": {
    "build": "cd apps/web && next build && cd ../api && tsc",
    "lint": "eslint apps/ packages/",
    "test": "vitest"
  }
}

Root Tasks (//#taskname) are ONLY for tasks that truly cannot exist in packages (rare).

Secondary Rule: turbo run vs turbo

Always use turbo run when the command is written into code:

// package.json - ALWAYS "turbo run"
{
  "scripts": {
    "build": "turbo run build"
  }
}

# CI workflows - ALWAYS "turbo run"
- run: turbo run build --affected

The shorthand turbo <tasks> is ONLY for one-off terminal commands typed directly by humans or agents. Never write turbo build into package.json, CI, or scripts.

Quick Decision Trees

"I need to configure a task"

Configure a task?
├─ Define task dependencies → references/configuration/tasks.md
├─ Lint/check-types (parallel + caching) → Use Transit Nodes pattern (see below)
├─ Specify build outputs → references/configuration/tasks.md#outputs
├─ Handle environment variables → references/environment/RULE.md
├─ Set up dev/watch tasks → references/configuration/tasks.md#persistent
├─ Package-specific config → references/configuration/RULE.md#package-configurations
└─ Global settings (cacheDir, daemon) → references/configuration/global-options.md

"My cache isn't working"

Cache problems?
├─ Tasks run but outputs not restored → Missing `outputs` key
├─ Cache misses unexpectedly → references/caching/gotchas.md
├─ Need to debug hash inputs → Use --summarize or --dry
├─ Want to skip cache entirely → Use --force or cache: false
├─ Remote cache not working → references/caching/remote-cache.md
└─ Environment causing misses → references/environment/gotchas.md

"I want to run only changed packages"

Run only what changed?
├─ Changed packages + dependents (RECOMMENDED) → turbo run build --affected
├─ Custom base branch → --affected --affected-base=origin/develop
├─ Manual git comparison → --filter=...[origin/main]
└─ See all filter options → references/filtering/RULE.md

--affected is the primary way to run only changed packages. It automatically compares against the default branch and includes dependents.

"I want to filter packages"

Filter packages?
├─ Only changed packages → --affected (see above)
├─ By package name → --filter=web
├─ By directory → --filter=./apps/*
├─ Package + dependencies → --filter=web...
├─ Package + dependents → --filter=...web
└─ Complex combinations → references/filtering/patterns.md

"Environment variables aren't working"

Environment issues?
├─ Vars not available at runtime → Strict mode filtering (default)
├─ Cache hits with wrong env → Var not in `env` key
├─ .env changes not causing rebuilds → .env not in `inputs`
├─ CI variables missing → references/environment/gotchas.md
└─ Framework vars (NEXT_PUBLIC_*) → Auto-included via inference

"I need to set up CI"

CI setup?
├─ GitHub Actions → references/ci/github-actions.md
├─ Vercel deployment → references/ci/vercel.md
├─ Remote cache in CI → references/caching/remote-cache.md
├─ Only build changed packages → --affected flag
├─ Skip unnecessary builds → turbo-ignore (references/cli/commands.md)
└─ Skip container setup when no changes → turbo-ignore

"I want to watch for changes during development"

Watch mode?
├─ Re-run tasks on change → turbo watch (references/watch/RULE.md)
├─ Dev servers with dependencies → Use `with` key (references/configuration/tasks.md#with)
├─ Restart dev server on dep change → Use `interruptible: true`
└─ Persistent dev tasks → Use `persistent: true`

"I need to create/structure a package"

Package creation/structure?
├─ Create an internal package → references/best-practices/packages.md
├─ Repository structure → references/best-practices/structure.md
├─ Dependency management → references/best-practices/dependencies.md
├─ Best practices overview → references/best-practices/RULE.md
├─ JIT vs Compiled packages → references/best-practices/packages.md#compilation-strategies
└─ Sharing code between apps → references/best-practices/RULE.md#package-types

"How should I structure my monorepo?"

Monorepo structure?
├─ Standard layout (apps/, packages/) → references/best-practices/RULE.md
├─ Package types (apps vs libraries) → references/best-practices/RULE.md#package-types
├─ Creating internal packages → references/best-practices/packages.md
├─ TypeScript configuration → references/best-practices/structure.md#typescript-configuration
├─ ESLint configuration → references/best-practices/structure.md#eslint-configuration
├─ Dependency management → references/best-practices/dependencies.md
└─ Enforce package boundaries → references/boundaries/RULE.md

"I want to enforce architectural boundaries"

Enforce boundaries?
├─ Check for violations → turbo boundaries
├─ Tag packages → references/boundaries/RULE.md#tags
├─ Restrict which packages can import others → references/boundaries/RULE.md#rule-types
└─ Prevent cross-package file imports → references/boundaries/RULE.md

Critical Anti-Patterns

Using turbo Shorthand in Code

turbo run is recommended in package.json scripts and CI pipelines. The shorthand turbo <task> is intended for interactive terminal use.

// WRONG - using shorthand in package.json
{
  "scripts": {
    "build": "turbo build",
    "dev": "turbo dev"
  }
}

// CORRECT
{
  "scripts": {
    "build": "turbo run build",
    "dev": "turbo run dev"
  }
}

# WRONG - using shorthand in CI
- run: turbo build --affected

# CORRECT
- run: turbo run build --affected

Root Scripts Bypassing Turbo

Root package.json scripts MUST delegate to turbo run, not run tasks directly.

// WRONG - bypasses turbo entirely
{
  "scripts": {
    "build": "bun build",
    "dev": "bun dev"
  }
}

// CORRECT - delegates to turbo
{
  "scripts": {
    "build": "turbo run build",
    "dev": "turbo run dev"
  }
}

Using && to Chain Turbo Tasks

Don't chain turbo tasks with &&. Let turbo orchestrate.

// WRONG - turbo task not using turbo run
{
  "scripts": {
    "changeset:publish": "bun build && changeset publish"
  }
}

// CORRECT
{
  "scripts": {
    "changeset:publish": "turbo run build && changeset publish"
  }
}

prebuild Scripts That Manually Build Dependencies

Scripts like prebuild that manually build other packages bypass Turborepo's dependency graph.

// WRONG - manually building dependencies
{
  "scripts": {
    "prebuild": "cd ../../packages/types && bun run build && cd ../utils && bun run build",
    "build": "next build"
  }
}

However, the fix depends on whether workspace dependencies are declared:

1. If dependencies ARE declared (e.g., "@repo/types": "workspace:*" in package.json), remove the prebuild script. Turbo's dependsOn: ["^build"] handles this automatically.

2. If dependencies are NOT declared, the prebuild exists because ^build won't trigger without a dependency relationship. The fix is to:

   • Add the dependency to package.json: "@repo/types": "workspace:*"
   • Then remove the prebuild script

// CORRECT - declare dependency, let turbo handle build order
// package.json
{
  "dependencies": {
    "@repo/types": "workspace:*",
    "@repo/utils": "workspace:*"
  },
  "scripts": {
    "build": "next build"
  }
}

// turbo.json
{
  "tasks": {
    "build": {
      "dependsOn": ["^build"]
    }
  }
}

Key insight: ^build only runs build in packages listed as dependencies. No dependency declaration = no automatic build ordering.

Overly Broad globalDependencies

globalDependencies affects ALL tasks in ALL packages. Be specific.

// WRONG - heavy hammer, affects all hashes
{
  "globalDependencies": ["**/.env.*local"]
}

// BETTER - move to task-level inputs
{
  "globalDependencies": [".env"],
  "tasks": {
    "build": {
      "inputs": ["$TURBO_DEFAULT$", ".env*"],
      "outputs": ["dist/**"]
    }
  }
}

Repetitive Task Configuration

Look for repeated configuration across tasks that can be collapsed. Turborepo supports shared configuration patterns.

// WRONG - repetitive env and inputs across tasks
{
  "tasks": {
    "build": {
      "env": ["API_URL", "DATABASE_URL"],
      "inputs": ["$TURBO_DEFAULT$", ".env*"]
    },
    "test": {
      "env": ["API_URL", "DATABASE_URL"],
      "inputs": ["$TURBO_DEFAULT$", ".env*"]
    },
    "dev": {
      "env": ["API_URL", "DATABASE_URL"],
      "inputs": ["$TURBO_DEFAULT$", ".env*"],
      "cache": false,
      "persistent": true
    }
  }
}

// BETTER - use globalEnv and globalDependencies for shared config
{
  "globalEnv": ["API_URL", "DATABASE_URL"],
  "globalDependencies": [".env*"],
  "tasks": {
    "build": {},
    "test": {},
    "dev": {
      "cache": false,
      "persistent": true
    }
  }
}

When to use global vs task-level:

• globalEnv / globalDependencies - affects ALL tasks, use for truly shared config
• Task-level env / inputs - use when only specific tasks need it

NOT an Anti-Pattern: Large env Arrays

A large env array (even 50+ variables) is not a problem. It usually means the user was thorough about declaring their build's environment dependencies. Do not flag this as an issue.

Using --parallel Flag

The --parallel flag bypasses Turborepo's dependency graph. If tasks need parallel execution, configure dependsOn correctly instead.

# WRONG - bypasses dependency graph
turbo run lint --parallel

# CORRECT - configure tasks to allow parallel execution
# In turbo.json, set dependsOn appropriately (or use transit nodes)
turbo run lint

Package-Specific Task Overrides in Root turbo.json

When multiple packages need different task configurations, use Package Configurations (turbo.json in each package) instead of cluttering root turbo.json with package#task overrides.

// WRONG - root turbo.json with many package-specific overrides
{
  "tasks": {
    "test": { "dependsOn": ["build"] },
    "@repo/web#test": { "outputs": ["coverage/**"] },
    "@repo/api#test": { "outputs": ["coverage/**"] },
    "@repo/utils#test": { "outputs": [] },
    "@repo/cli#test": { "outputs": [] },
    "@repo/core#test": { "outputs": [] }
  }
}

// CORRECT - use Package Configurations
// Root turbo.json - base config only
{
  "tasks": {
    "test": { "dependsOn": ["build"] }
  }
}

// packages/web/turbo.json - package-specific override
{
  "extends": ["//"],
  "tasks": {
    "test": { "outputs": ["coverage/**"] }
  }
}

// packages/api/turbo.json
{
  "extends": ["//"],
  "tasks": {
    "test": { "outputs": ["coverage/**"] }
  }
}

Benefits of Package Configurations:

• Keeps configuration close to the code it affects
• Root turbo.json stays clean and focused on base patterns
• Easier to understand what's special about each package
• Works with $TURBO_EXTENDS$ to inherit + extend arrays

When to use package#task in root:

• Single package needs a unique dependency (e.g., "deploy": { "dependsOn": ["web#build"] })
• Temporary override while migrating

See references/configuration/RULE.md#package-configurations for full details.

Using ../ to Traverse Out of Package in inputs

Don't use relative paths like ../ to reference files outside the package. Use $TURBO_ROOT$ instead.

// WRONG - traversing out of package
{
  "tasks": {
    "build": {
      "inputs": ["$TURBO_DEFAULT$", "../shared-config.json"]
    }
  }
}

// CORRECT - use $TURBO_ROOT$ for repo root
{
  "tasks": {
    "build": {
      "inputs": ["$TURBO_DEFAULT$", "$TURBO_ROOT$/shared-config.json"]
    }
  }
}

Missing outputs for File-Producing Tasks

Before flagging missing outputs, check what the task actually produces:

1. Read the package's script (e.g., "build": "tsc", "test": "vitest")
2. Determine if it writes files to disk or only outputs to stdout
3. Only flag if the task produces files that should be cached

// WRONG: build produces files but they're not cached
{
  "tasks": {
    "build": {
      "dependsOn": ["^build"]
    }
  }
}

// CORRECT: build outputs are cached
{
  "tasks": {
    "build": {
      "dependsOn": ["^build"],
      "outputs": ["dist/**"]
    }
  }
}

Common outputs by framework:

• Next.js: [".next/**", "!.next/cache/**"]
• Vite/Rollup: ["dist/**"]
• tsc: ["dist/**"] or custom outDir

TypeScript --noEmit can still produce cache files:

When incremental: true in tsconfig.json, tsc --noEmit writes .tsbuildinfo files even without emitting JS. Check the tsconfig before assuming no outputs:

// If tsconfig has incremental: true, tsc --noEmit produces cache files
{
  "tasks": {
    "typecheck": {
      "outputs": ["node_modules/.cache/tsbuildinfo.json"] // or wherever tsBuildInfoFile points
    }
  }
}

To determine correct outputs for TypeScript tasks:

1. Check if incremental or composite is enabled in tsconfig
2. Check tsBuildInfoFile for custom cache location (default: alongside outDir or in project root)
3. If no incremental mode, tsc --noEmit produces no files

^build vs build Confusion

{
  "tasks": {
    // ^build = run build in DEPENDENCIES first (other packages this one imports)
    "build": {
      "dependsOn": ["^build"]
    },
    // build (no ^) = run build in SAME PACKAGE first
    "test": {
      "dependsOn": ["build"]
    },
    // pkg#task = specific package's task
    "deploy": {
      "dependsOn": ["web#build"]
    }
  }
}

Environment Variables Not Hashed

// WRONG: API_URL changes won't cause rebuilds
{
  "tasks": {
    "build": {
      "outputs": ["dist/**"]
    }
  }
}

// CORRECT: API_URL changes invalidate cache
{
  "tasks": {
    "build": {
      "outputs": ["dist/**"],
      "env": ["API_URL", "API_KEY"]
    }
  }
}

.env Files Not in Inputs

Turbo does NOT load .env files - your framework does. But Turbo needs to know about changes:

// WRONG: .env changes don't invalidate cache
{
  "tasks": {
    "build": {
      "env": ["API_URL"]
    }
  }
}

// CORRECT: .env file changes invalidate cache
{
  "tasks": {
    "build": {
      "env": ["API_URL"],
      "inputs": ["$TURBO_DEFAULT$", ".env", ".env.*"]
    }
  }
}

Root .env File in Monorepo

A .env file at the repo root is an anti-pattern — even for small monorepos or starter templates. It creates implicit coupling between packages and makes it unclear which packages depend on which variables.

// WRONG - root .env affects all packages implicitly
my-monorepo/
├── .env              # Which packages use this?
├── apps/
│   ├── web/
│   └── api/
└── packages/

// CORRECT - .env files in packages that need them
my-monorepo/
├── apps/
│   ├── web/
│   │   └── .env      # Clear: web needs DATABASE_URL
│   └── api/
│       └── .env      # Clear: api needs API_KEY
└── packages/

Problems with root .env:

• Unclear which packages consume which variables
• All packages get all variables (even ones they don't need)
• Cache invalidation is coarse-grained (root .env change invalidates everything)
• Security risk: packages may accidentally access sensitive vars meant for others
• Bad habits start small — starter templates should model correct patterns

If you must share variables, use globalEnv to be explicit about what's shared, and document why.

Strict Mode Filtering CI Variables

By default, Turborepo filters environment variables to only those in env/globalEnv. CI variables may be missing:

// If CI scripts need GITHUB_TOKEN but it's not in env:
{
  "globalPassThroughEnv": ["GITHUB_TOKEN", "CI"],
  "tasks": { ... }
}

Or use --env-mode=loose (not recommended for production).

Shared Code in Apps (Should Be a Package)

// WRONG: Shared code inside an app
apps/
  web/
    shared/          # This breaks monorepo principles!
      utils.ts

// CORRECT: Extract to a package
packages/
  utils/
    src/utils.ts

Accessing Files Across Package Boundaries

// WRONG: Reaching into another package's internals
import { Button } from "../../packages/ui/src/button";

// CORRECT: Install and import properly
import { Button } from "@repo/ui/button";

Too Many Root Dependencies

// WRONG: App dependencies in root
{
  "dependencies": {
    "react": "^18",
    "next": "^14"
  }
}

// CORRECT: Only repo tools in root
{
  "devDependencies": {
    "turbo": "latest"
  }
}

Common Task Configurations

Standard Build Pipeline

{
  "$schema": "https://v2-8-15-canary-6.turborepo.dev/schema.json",
  "tasks": {
    "build": {
      "dependsOn": ["^build"],
      "outputs": ["dist/**", ".next/**", "!.next/cache/**"]
    },
    "dev": {
      "cache": false,
      "persistent": true
    }
  }
}

Add a transit task if you have tasks that need parallel execution with cache invalidation (see below).

Dev Task with ^dev Pattern (for turbo watch)

A dev task with dependsOn: ["^dev"] and persistent: false in root turbo.json may look unusual but is correct for turbo watch workflows:

// Root turbo.json
{
  "tasks": {
    "dev": {
      "dependsOn": ["^dev"],
      "cache": false,
      "persistent": false  // Packages have one-shot dev scripts
    }
  }
}

// Package turbo.json (apps/web/turbo.json)
{
  "extends": ["//"],
  "tasks": {
    "dev": {
      "persistent": true  // Apps run long-running dev servers
    }
  }
}

Why this works:

• Packages (e.g., @acme/db, @acme/validators) have "dev": "tsc" — one-shot type generation that completes quickly
• Apps override with persistent: true for actual dev servers (Next.js, etc.)
• turbo watch re-runs the one-shot package dev scripts when source files change, keeping types in sync

Intended usage: Run turbo watch dev (not turbo run dev). Watch mode re-executes one-shot tasks on file changes while keeping persistent tasks running.

Alternative pattern: Use a separate task name like prepare or generate for one-shot dependency builds to make the intent clearer:

{
  "tasks": {
    "prepare": {
      "dependsOn": ["^prepare"],
      "outputs": ["dist/**"]
    },
    "dev": {
      "dependsOn": ["prepare"],
      "cache": false,
      "persistent": true
    }
  }
}

Transit Nodes for Parallel Tasks with Cache Invalidation

Some tasks can run in parallel (don't need built output from dependencies) but must invalidate cache when dependency source code changes.

The problem with dependsOn: ["^taskname"]:

• Forces sequential execution (slow)

The problem with dependsOn: [] (no dependencies):

• Allows parallel execution (fast)
• But cache is INCORRECT - changing dependency source won't invalidate cache

Transit Nodes solve both:

{
  "tasks": {
    "transit": { "dependsOn": ["^transit"] },
    "my-task": { "dependsOn": ["transit"] }
  }
}

The transit task creates dependency relationships without matching any actual script, so tasks run in parallel with correct cache invalidation.

How to identify tasks that need this pattern: Look for tasks that read source files from dependencies but don't need their build outputs.

With Environment Variables

{
  "globalEnv": ["NODE_ENV"],
  "globalDependencies": [".env"],
  "tasks": {
    "build": {
      "dependsOn": ["^build"],
      "outputs": ["dist/**"],
      "env": ["API_URL", "DATABASE_URL"]
    }
  }
}

Reference Index

Configuration

Caching

Environment Variables

Filtering

CI/CD

CLI

Best Practices

Watch Mode

Boundaries (Experimental)

Source Documentation

This skill is based on the official Turborepo documentation at:

• Source: apps/docs/content/docs/ in the Turborepo repository
• Live: https://turborepo.dev/docs

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