| name | homebrew-formula |
| description | Create, test, and maintain Homebrew formulas. Use when adding packages to a Homebrew tap, debugging formula issues, running brew audit/test, or automating version updates with livecheck. |
Homebrew Formula Development
Guide for researching, creating, testing, and maintaining Homebrew formulas in a custom tap.
When to Use This Skill
- Creating a new Homebrew formula for a project
- Debugging formula build or test failures
- Running local validation before CI
- Understanding Homebrew's Ruby DSL
- Setting up livecheck for automatic version detection
Research Phase
Before creating a formula, gather this information:
Required Information
| Field | How to Find |
|---|
| Latest version | gh release view --repo owner/repo --json tagName |
| License | Check LICENSE file or repo metadata (use SPDX identifier) |
| Build system | Look at Makefile, go.mod, Cargo.toml, package.json, etc. |
| Dependencies | Check build docs, CI files, or dependency manifests |
| Binary location | For Go: check for cmd/ directory or main.go location |
Calculate SHA256
Always calculate the checksum for the source tarball:
curl -sL "https://github.com/owner/repo/archive/refs/tags/vX.Y.Z.tar.gz" | shasum -a 256
Formula Structure
File Location
Formulas are organized alphabetically: Formula/<first-letter>/<name>.rb
Example: Formula/m/mustache.rb
Template
See the slash command /add-homebrew-formula for a complete template, or reference existing formulas in Formula/ directory.
Key Elements
| Element | Purpose |
|---|
desc | Short description (~80 chars) for brew info |
homepage | Project's homepage URL |
url | Source tarball URL (prefer source over pre-built binaries) |
sha256 | Checksum for integrity verification |
license | SPDX identifier (MIT, Apache-2.0, GPL-3.0, etc.) |
head | Git URL for --HEAD installs |
depends_on | Build or runtime dependencies |
test | Verification block that proves the install works |
Language-Specific Patterns
Go Projects:
depends_on "go" => :build
def install
system "go", "build", *std_go_args(ldflags: "-s -w"), "./cmd/binary"
end
Rust Projects:
depends_on "rust" => :build
def install
system "cargo", "install", *std_cargo_args
end
Local Validation
Step 1: Sync to Tap Location
Formula files must be in the Homebrew tap location for testing:
mkdir -p /usr/local/Homebrew/Library/Taps/arustydev/homebrew-tap/Formula/<letter>/
cp Formula/<letter>/<name>.rb /usr/local/Homebrew/Library/Taps/arustydev/homebrew-tap/Formula/<letter>/
chmod a+r /usr/local/Homebrew/Library/Taps/arustydev/homebrew-tap/Formula/<letter>/<name>.rb
Step 2: Run Audit
brew audit --new --formula arustydev/tap/<name>
This checks for common formula issues but NOT style violations.
Step 3: Run CI Syntax Check (Critical)
brew test-bot --only-tap-syntax
This runs brew style (rubocop) against ALL files in the tap - same as CI. This catches issues that brew audit misses.
Step 4: Test Installation
brew install --build-from-source arustydev/tap/<name>
Step 5: Run Formula Tests
brew test arustydev/tap/<name>
Step 6: Verify Binary
<name> --help
Version Updates with Livecheck
Homebrew's livecheck automatically detects new versions from the formula's URL pattern. No manual version registry needed.
Test livecheck:
brew livecheck arustydev/tap/<name>
Common Issues
CI Failures from Rubocop
Problem: brew test-bot --only-tap-syntax fails on markdown files containing Ruby code blocks.
Cause: brew style uses rubocop-md which lints code fenced as ruby in markdown files. The tap's .rubocop.yml exclusions do NOT apply - brew style uses Homebrew's central config.
Solution: Use text instead of ruby for code fence language in any markdown documentation.
Line Length Errors
Problem: Lines longer than 118 characters.
Solution: Split long strings or use Homebrew's allowed patterns (URLs, sha256 lines, etc. are exempt).
Test Block Failures
Problem: Formula installs but brew test fails.
Solution: Ensure test block creates necessary test files and uses proper paths:
test do
(testpath/"input.txt").write("test content")
output = shell_output("#{bin}/tool #{testpath}/input.txt")
assert_equal "expected", output.strip
end
Checklist
References
