Lesson Content

Skill file structure.

A Skill is a markdown file with a frontmatter header and instruction content (verify current format at docs.anthropic.com/en/docs/claude-code):

—
name: pr-code-review
description: Step-by-step code review checklist for pull requests
triggers:
– "review this PR"
– "review this code"
– "code review"
– "check this diff"
—

## PR Code Review Checklist

When reviewing a PR, check in this order:

1. **Security**: Input validation on user-supplied data, authentication/authorization checks, no hardcoded credentials
2. **Test coverage**: Are the happy path and error cases covered? Do tests test behavior or implementation?
3. **Error handling**: Are errors caught and handled or propagated appropriately?
4. **Readability**: Variable names, function names, and logic are clear without comments
5. **Performance**: Are there obvious N+1 queries, unnecessary re-computation, or missing indexes?

For each item: pass, flag for discussion, or request change.

Writing effective triggers.

Triggers are the phrases or conditions that activate the Skill. Effective triggers:

• Match the natural language a user would use when requesting the task
• Include variations (formal and informal phrasings)
• Are specific enough to avoid false activation
• Are not so narrow that they miss legitimate requests

For a code review Skill: ["review this PR", "code review", "review this code", "check this diff", "review my changes"] – multiple phrasings of the same intent.

Instruction structure for Skills.

Structure Skill instructions as procedural guidance Claude follows:

• Use numbered steps for ordered workflows
• Use checklists for evaluation tasks
• Use clear headers to organize multi-part instructions
• Keep instructions actionable ("check for X", "verify that Y") not descriptive ("X is important")

Common Skill writing mistakes.

• Triggers too broad: A trigger of "code" activates for any code-related task – not just review
• Triggers too narrow: A trigger of "review PR #123" activates for nothing useful
• Instructions too vague: "Review for quality" is not actionable; "Check for unhandled null returns" is
• Instructions too long: A 500-word Skill dilutes the key points; keep Skills focused on the most important checks for the specific task