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What is Grog?

Grog is a lightweight build orchestrator that runs your existing commands in parallel —rebuilding only what’s changed— while caching the results for future runs. It’s designed to be a simple and lightweight alternative to existing build systems like Bazel, Buck, and Pants.

Unlike those build systems, Grog remains agnostic to the actual build execution. This means that you can keep using your existing scripts, Makefile rules, NPM commands, or any CLI you love—while grog transparently handles change detection, (remote) caching, and concurrent execution. This allows small teams to get an immediate boost to their monorepo productivity without having to buy into a complex tool.

Read more in Why Grog?.

1. Install Grog

Terminal window
# Using Homebrew
brew tap chrismatix/grog
brew install grog


# Or download the binary
curl -L https://grog.build/latest/grog-darwin-arm64 -o /usr/local/bin/grog
chmod +x /usr/local/bin/grog

2. Initialize The Repository

To start using Grog in your project, you need to initialize it by creating a grog.toml file at the root of your repository:

Terminal window
touch grog.toml

A minimal grog.toml file can be empty, with all settings using default values. Refer to the configuration reference to see all available options.

3. Define BUILD Files

BUILD files define your build targets. Each target is a command that runs when its file inputs or dependencies change. Grog provides a wide array of build file formats:

BUILD.yaml
targets:
  - name: build_ui
    command: npm run build:ui
    inputs:
      - frontend/src/**/*.{js,ts,jsx,tsx}
      - frontend/package.json
    outputs:
      - dir::frontend/dist


  - name: compile_backend
    command: go build -o backend/bin/app ./backend
    inputs:
      - backend/**/*.go
    outputs:
      - backend/bin/app


  - name: build_image
    command: >
      docker build \
      --file Dockerfile \
      --tag myorg/myapp:latest .
    dependencies:
      - :build_ui
      - :compile_backend
    inputs:
      - Dockerfile
    outputs:
      - docker::myorg/myapp:latest

Save this as BUILD.yaml in your project directory.

Things to note from the above examples:

  • Targets are referenced using labels.
  • Directory outputs are prefixed with dir:: to indicate they are directories.
  • Command definition command are executed as sh scripts in the target’s directory.

4. Inspect the Build Graph

The build targets defined in the example above form a directed acyclic (build) graph (DAG). You can visualize this graph using the grog graph command:

---
title: get_started dependency graph
config:
    theme: default
    maxTextSize: 50000
    maxEdges: 500
    fontSize: 16
---
flowchart BT
    0@{ shape: rect, label: "//:build_image"}
    style 0 fill:#E3F2FD,stroke:#1E88E5,stroke-width:2
    1@{ shape: rect, label: "Dockerfile"}
    style 1 fill:#FFF8E1,stroke:#FB8C00,stroke-width:2,stroke-dasharray:6 3
    2@{ shape: rect, label: "//:build_ui"}
    style 2 fill:#E3F2FD,stroke:#1E88E5,stroke-width:2
    3@{ shape: rect, label: "frontend/package.json"}
    style 3 fill:#FFF8E1,stroke:#FB8C00,stroke-width:2,stroke-dasharray:6 3
    4@{ shape: rect, label: "frontend/src/*"}
    style 4 fill:#FFF8E1,stroke:#FB8C00,stroke-width:2,stroke-dasharray:6 3
    5@{ shape: rect, label: "//:compile_backend"}
    style 5 fill:#E3F2FD,stroke:#1E88E5,stroke-width:2
    6@{ shape: rect, label: "backend/**/*.go"}
    style 6 fill:#FFF8E1,stroke:#FB8C00,stroke-width:2,stroke-dasharray:6 3
    1 -.-> 0
    3 -.-> 2
    4 -.-> 2
    6 -.-> 5
    2 --> 0
    5 --> 0

This representation reveals a few things:

  • Grog can and will build compile_backend and build_ui in parallel before building build_image.
  • A change to any file in backend/**/*.go will trigger a rebuild of compile_backend. This will in turn trigger a rebuild of build_image.

5. Run Builds

To run a build, use the grog build command followed by the target label:

Terminal window
# Build a specific target
grog build //path/to/package:target_name


# Build all targets in and below a package
grog build //path/to/package/...


# Build all targets
grog build

Grog will re-run a build if any of the following conditions are met:

  • A target’s definition has changed.
  • A target’s inputs have changed.
  • A target’s dependencies have changed.

6. Run Tests

Grog will automatically treat targets that end with test as test targets. They will only be executed if you run grog test and will be ignored for grog build

Target Overview

Now we will look at the most important fields you can define on a target. You can find the complete target configuration reference here.

Inputs

Inputs are files that your build target depends on. When any of these files change, Grog will re-run the target’s command. You can specify inputs using file paths or glob patterns:

inputs:
  - "src/**/*.js"
  - package.json
  - "assets/*.{png,jpg}"
  • src/**/*.js - All JavaScript files in src directory and subdirectories
  • package.json - A specific file
  • assets/*.{png,jpg} - All PNG and JPG files in assets directory

Grog tracks inputs by computing a hash of their contents. This allows it to detect changes and only rebuild when necessary.

Dependencies

Dependencies are other targets that must be built before the current target. This creates a directed acyclic graph (DAG) of build steps:

dependencies:
  - :generate_proto
  - //lib:build_lib
  • generate_proto - A dependency on another target in the same package
  • //lib:build_lib - A dependency on a target in another package

When you specify dependencies:

  • Grog ensures they are built before the current target.
  • Changes to a dependency’s outputs will trigger a rebuild of dependent targets.
  • Grog can parallelize the build by running independent targets concurrently.

Outputs

Outputs are artifacts that your build target produces and who you might want to share between machines using a remote cache. Grog, therefore, caches these outputs and restores them when possible to avoid unnecessary rebuilds.

outputs:
  - dist/bundle.js
  - dir::dist/assets/
  - docker::some-image
  • dist/bundle.js - A file output
  • dir::dist/assets/ - A directory output
  • docker::some-image-tag - A Docker image output

Next Steps

Now that you’ve set up Grog and created your first build targets, you might want to explore: