moon — Rust-Powered Build System for Web Monorepos

Introduction

moon is a build system and monorepo management tool built in Rust by moonrepo. It brings fast, reproducible task execution to JavaScript, TypeScript, and polyglot web projects with features like dependency-aware task orchestration, remote caching, and automatic affected-project detection.

What moon Does

• Orchestrates tasks across monorepo packages with dependency awareness
• Detects affected projects from Git changes for efficient CI runs
• Provides remote caching to skip redundant builds across machines
• Manages toolchain versions (Node.js, Bun, Deno, Go, Python, Rust) automatically
• Generates project graphs and dependency visualizations

Architecture Overview

moon uses a Rust core for performance-critical operations: hashing, dependency resolution, and task scheduling. Projects are defined in moon.yml files, and tasks run through a DAG-based executor that respects inter-project dependencies. The toolchain manager downloads and pins exact runtime versions per project. Remote caching stores task outputs keyed by input hashes, shared via moonbase or custom backends.

Self-Hosting & Configuration

• Install the moon binary via the official install script or npm
• Run moon init to scaffold configuration in your monorepo root
• Define projects in .moon/workspace.yml and tasks in per-project moon.yml
• Configure remote caching with moonbase or a custom S3-compatible backend
• Integrate moon ci into your CI pipeline for affected-only builds

Key Features

• Rust-powered performance with sub-millisecond task hashing
• Automatic toolchain version management across the team
• Built-in affected-project detection from Git diff analysis
• Remote caching to eliminate redundant CI work
• First-class support for JavaScript, TypeScript, Bun, Deno, Go, Python, and Rust

Comparison with Similar Tools

• Turborepo — JS-focused, simpler but less polyglot support
• Nx — feature-rich but heavier, Node.js-based runtime
• Bazel — extremely powerful but steep learning curve for web teams
• Lerna — monorepo publishing tool, not a build system
• Pants — Python-focused polyglot build system, less web-oriented

FAQ

Q: Does moon replace npm/pnpm/yarn? A: No. moon orchestrates tasks on top of your existing package manager. It manages when and in what order tasks run, not package installation.

Q: How does affected detection work? A: moon computes a hash of each project's source files and dependencies from the Git diff. Only projects with changed inputs (or downstream dependents) run in CI.

Q: Can I use moon for non-JavaScript projects? A: Yes. moon supports Go, Python, and Rust toolchains alongside JavaScript/TypeScript, making it suitable for polyglot monorepos.

Q: How does remote caching work? A: Task outputs are stored in a remote cache keyed by input hash. When another developer or CI run encounters the same inputs, the cached output is restored instead of re-running the task.

Sources

• https://github.com/moonrepo/moon
• https://moonrepo.dev