nixpacks
Expert guidance for Nixpacks, the build system created by Railway that automatically detects your application's language and framework, installs dependencies, and produces optimized Docker images — all without writing a Dockerfile. Helps developers configure Nixpacks for custom build steps, multi-language projects, and CI/CD integration.
Usage
Getting Started
- Install the skill using the command above
- Open your AI coding agent (Claude Code, Codex, Gemini CLI, or Cursor)
- Reference the skill in your prompt
- The AI will use the skill's capabilities automatically
Example Prompts
- "Deploy the latest build to the staging environment and run smoke tests"
- "Check the CI pipeline status and summarize any recent failures"
Documentation
Overview
Nixpacks, the build system created by Railway that automatically detects your application's language and framework, installs dependencies, and produces optimized Docker images — all without writing a Dockerfile. Helps developers configure Nixpacks for custom build steps, multi-language projects, and CI/CD integration.
Instructions
Basic Usage
Build any application into a Docker image:
# Install Nixpacks
curl -sSL https://nixpacks.com/install.sh | bash
# Build an image (auto-detects language and framework)
nixpacks build ./my-node-app -n my-app
# Detects: Node.js + Next.js → installs Node, npm ci, npm run build
nixpacks build ./my-python-api -n my-api
# Detects: Python + FastAPI → installs Python, pip install, uvicorn start
nixpacks build ./my-rust-service -n my-service
# Detects: Rust + Cargo → installs Rust, cargo build --release
# Run the built image
docker run -p 3000:3000 my-app
# Generate a Dockerfile without building (inspect what Nixpacks would do)
nixpacks plan ./my-node-app
# Shows: detected providers, install/build/start commands, Nix packages
# Generate Dockerfile for manual editing
nixpacks build ./my-node-app --out . --name my-app
# Creates .nixpacks/Dockerfile that you can customize
Configuration
Override auto-detected settings:
# nixpacks.toml — Custom build configuration
[phases.setup]
# Additional system packages (via Nix)
nixPkgs = ["ffmpeg", "imagemagick", "poppler_utils"]
aptPkgs = ["libvips-dev"] # Debian packages (fallback)
[phases.install]
cmds = ["npm ci --production=false"] # Override install command
[phases.build]
cmds = [
"npx prisma generate", # Generate Prisma client
"npm run build", # Build the application
]
[start]
cmd = "node dist/server.js" # Override start command
# Environment variables available during build
[variables]
NODE_ENV = "production"
NEXT_TELEMETRY_DISABLED = "1"
# nixpacks.toml — Python project with system dependencies
[phases.setup]
nixPkgs = ["postgresql"] # For psycopg2 compilation
pythonVersion = "3.12"
[phases.install]
cmds = ["pip install -r requirements.txt"]
[phases.build]
cmds = [
"python manage.py collectstatic --noinput",
"python manage.py migrate --check",
]
[start]
cmd = "gunicorn myapp.wsgi:application --bind 0.0.0.0:$PORT --workers 4"
Multi-Language Projects
Handle monorepos and multi-language apps:
# nixpacks.toml — Monorepo with frontend + backend
[phases.setup]
nixPkgs = ["nodejs-20_x", "python312"]
[phases.install]
cmds = [
"cd frontend && npm ci",
"cd backend && pip install -r requirements.txt",
]
[phases.build]
cmds = [
"cd frontend && npm run build",
"cp -r frontend/dist backend/static",
"cd backend && python manage.py collectstatic --noinput",
]
[start]
cmd = "cd backend && gunicorn app:app --bind 0.0.0.0:$PORT"
CI/CD Integration
Use Nixpacks in GitHub Actions:
# .github/workflows/deploy.yml — Build and push with Nixpacks
name: Deploy
on:
push:
branches: [main]
jobs:
build-and-deploy:
runs-on: ubuntu-latest
steps:
- uses: actions/checkout@v4
- name: Install Nixpacks
run: curl -sSL https://nixpacks.com/install.sh | bash
- name: Build image
run: |
nixpacks build . \
--name ghcr.io/${{ github.repository }}:${{ github.sha }} \
--env NODE_ENV=production
- name: Login to GHCR
run: echo "${{ secrets.GITHUB_TOKEN }}" | docker login ghcr.io -u ${{ github.actor }} --password-stdin
- name: Push image
run: |
docker push ghcr.io/${{ github.repository }}:${{ github.sha }}
docker tag ghcr.io/${{ github.repository }}:${{ github.sha }} ghcr.io/${{ github.repository }}:latest
docker push ghcr.io/${{ github.repository }}:latest
Supported Languages
## Auto-Detected Languages and Frameworks
| Language | Detection File | Frameworks |
|-----------|------------------------|--------------------------------------|
| Node.js | package.json | Next.js, Nuxt, Remix, Express, Nest |
| Python | requirements.txt/pyproject.toml | Django, Flask, FastAPI, Streamlit |
| Rust | Cargo.toml | Actix, Axum, Rocket |
| Go | go.mod | Gin, Echo, Fiber, net/http |
| Ruby | Gemfile | Rails, Sinatra |
| PHP | composer.json | Laravel, Symfony |
| Java | pom.xml/build.gradle | Spring Boot, Quarkus |
| Elixir | mix.exs | Phoenix |
| Haskell | stack.yaml | - |
| Zig | build.zig | - |
| Crystal | shard.yml | - |
| Dart | pubspec.yaml | - |
| Swift | Package.swift | Vapor |
| .NET | *.csproj | ASP.NET |
| Static | index.html | - |
Examples
Example 1: Setting up Nixpacks for a microservices project
User request:
I have a Node.js API and a React frontend running in Docker. Set up Nixpacks for monitoring/deployment.
The agent creates the necessary configuration files based on patterns like # Install Nixpacks, sets up the integration with the existing Docker setup, configures appropriate defaults for a Node.js + React stack, and provides verification commands to confirm everything is working.
Example 2: Troubleshooting configuration issues
User request:
Nixpacks is showing errors in our configuration. Here are the logs: [error output]
The agent analyzes the error output, identifies the root cause by cross-referencing with common Nixpacks issues, applies the fix (updating configuration, adjusting resource limits, or correcting syntax), and verifies the resolution with appropriate health checks.
Guidelines
- Start without config — Try
nixpacks build .first; auto-detection handles most projects correctly - Use nixpacks.toml for system deps — Need FFmpeg, ImageMagick, or native libraries? Add them to
nixPkgs - Pin language versions — Specify
pythonVersion = "3.12"or use.nvmrc/.python-versionfiles - Check the plan first — Run
nixpacks plan .to see what Nixpacks will do before building - Cache layers — Nixpacks caches install and build phases; put dependency files (package.json) before source code
- Generate Dockerfile for debugging — Use
--out .to get the generated Dockerfile; inspect and customize if needed - Environment variables in build — Use
[variables]in nixpacks.toml for build-time vars; runtime vars come from your platform - Nix packages over apt — Prefer
nixPkgsoveraptPkgs; Nix packages are more reproducible and better cached
Information
- Version
- 1.0.0
- Author
- terminal-skills
- Category
- DevOps
- License
- Apache-2.0