usage-rules

name	usage-rules
description	Search for package-specific usage rules and best practices from Elixir packages. Use when you need coding conventions, patterns, common mistakes, or good/bad examples for packages like Ash, Phoenix, Ecto, etc.
allowed-tools	Read, Grep, Glob, Bash, AskUserQuestion
model	haiku
context	fork
agent	Explore
user-invocable	true

Usage Rules Search

Find package-specific best practices and coding conventions from usage-rules.md files.

What Are Usage Rules?

A community convention where packages include a usage-rules.md file with:

• Coding conventions and patterns
• Good/bad code examples (marked # GOOD, # BAD, # AVOID)
• Common mistakes to avoid
• Domain-specific idioms

Search Locations (in order)

1. Project deps: deps/<package>/usage-rules.md
2. Fetched cache: .usage-rules/<package>-<version>/usage-rules.md
3. Fetch if needed: Extract from package (see below)

Packages With Usage Rules

Primarily the Ash ecosystem:

• ash, ash_postgres, ash_phoenix, ash_json_api, ash_graphql
• spark, igniter, reactor

Most packages (Phoenix, Ecto, etc.) do not have usage-rules.md yet. For those, suggest hex-docs-search skill or official guides.

Fetching Usage Rules

# Fetch package and extract usage-rules.md
mix hex.package fetch <package> <version> --unpack --output .usage-rules/.tmp/<package>-<version>

# If usage-rules.md exists, copy to cache
if [ -f ".usage-rules/.tmp/<package>-<version>/usage-rules.md" ]; then
  mkdir -p ".usage-rules/<package>-<version>"
  cp ".usage-rules/.tmp/<package>-<version>/usage-rules.md" ".usage-rules/<package>-<version>/"
fi

# Clean up
rm -rf ".usage-rules/.tmp/<package>-<version>"

Mention adding .usage-rules/ to .gitignore once per session when fetching occurs.

Context-Aware Extraction

Usage rules files can be large. Extract relevant sections based on user's question:

User Context	Look for Sections
querying, filters	"Querying", "Filters", "Read Actions"
actions, create/update	"Actions", "Changes", "Validations"
relationships	"Relationships", "Aggregates"
errors, validation	"Error Handling", "Validations"
authorization	"Policies", "Authorization"
testing	"Testing"

Find section headings with line numbers, then extract the relevant section content.

Key Behaviors

• Extract relevant sections, don't dump entire file
• Highlight # GOOD vs # BAD patterns explicitly
• Note when package doesn't provide usage rules
• Suggest hex-docs-search for API documentation (complementary)
• Version awareness: prefer deps/ version over cached