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Overview

rninja is a high-performance, drop-in replacement for the Ninja build system, written in Rust. It maintains full compatibility with existing Ninja build files while adding powerful features like built-in caching and improved scheduling.

What is Ninja?

Ninja is a small, fast build system focused on speed. Unlike make or other build systems, Ninja is designed to have its input files generated by a higher-level build system like CMake, Meson, or GN. Its simplicity and speed have made it the build backend of choice for many large projects, including Chromium, Android, and LLVM.

What is rninja?

rninja takes everything that makes Ninja great and adds:

  • Built-in caching - Content-addressed artifact caching that persists across clean builds
  • Remote cache support - Share cached artifacts across your team and CI
  • Modern scheduler - Tokio-based async runtime for better CPU utilization
  • Daemon mode - Long-running process that caches parsed manifests

Key Features

Drop-in Compatibility

rninja reads the same build.ninja files that Ninja uses. You don't need to modify your build configuration or change how your build generator (CMake, Meson, GN) works.

# If this works...
ninja -C out/Release

# ...then this works too
rninja -C out/Release

All standard Ninja CLI flags are supported:

Flag Description
-C DIR Change to DIR before building
-f FILE Use FILE as the build file
-j N Run N jobs in parallel
-k N Keep going after N failures
-n Dry run
-v Verbose output
-d MODE Debug mode
-t TOOL Run a subtool

Content-Addressed Caching

rninja automatically caches build outputs based on their inputs:

  • BLAKE3 hashing for fast, secure content addressing
  • Local cache stored in ~/.cache/rninja by default
  • Automatic restoration when inputs match a cached build
  • Correct invalidation when any input changes

This means:

  • make clean && make becomes instant (cache hit)
  • Switching branches and back restores previous builds
  • CI builds can reuse artifacts from previous runs

Remote Cache Support

Share cached artifacts across machines:

export RNINJA_CACHE_REMOTE_SERVER=tcp://cache.internal:9999
export RNINJA_CACHE_TOKEN=your-token
rninja

Benefits:

  • CI runners share artifacts, reducing build times
  • Team members benefit from each other's builds
  • Remote-first or local-fallback modes available

Daemon Mode

rninja can run as a long-lived daemon that:

  • Caches parsed build.ninja manifests
  • Maintains warm file system caches
  • Handles multiple concurrent build requests
  • Auto-spawns when you run rninja

rninja vs Ninja

Feature Ninja rninja
Build file format .ninja .ninja (same)
CLI compatibility - Full
Build caching None Built-in
Remote cache None Built-in
No-op build speed ~0.23s ~0.01s
Daemon mode No Yes
Written in C++ Rust

When to Use rninja

rninja is ideal for:

  • Large C/C++ projects with long incremental build times
  • CI/CD pipelines where build time directly impacts costs
  • Monorepos where multiple teams share code
  • Teams that want to share build artifacts
  • Developers who frequently switch between branches

When NOT to Use rninja

rninja may not be necessary for:

  • Small projects where builds complete in seconds
  • Single-file builds with no caching benefit
  • Environments where Ninja isn't already in use

Next Steps