Creating Agent Skills

Skills extend agent capabilities with domain-specific knowledge. Use skills for procedural knowledge the agent lacks, not concepts it already understands.

If guidance is project-specific or one-off, use INSTRUCTIONS.md or inline context instead.

Create new skills under /Users/nicholasgriffin/Documents/GitHub/machine-setup/ai-tooling/skills .

Structure

Required Frontmatter

Every SKILL.md must start with YAML frontmatter on line 1:

name: my-skill-name description: What this skill does and when to use it. Third-person.

Field requirements:

• name : lowercase, hyphens only, max 64 chars, no reserved words ("anthropic", "claude")

• description : max 1024 chars, specific triggers + capabilities

File Organisation

skill-name/ ├── SKILL.md # Required. Under 200 lines. └── references/ # Optional. For detailed content. ├── api.md └── examples.md

Use references/ when SKILL.md exceeds 200 lines. Keep references one level deep and avoid nested references.

Writing Descriptions

The description determines when the skill activates. Include both what it does and when to use it.

Always use third-person (the description is injected into the system prompt):

Quality Example

Good Manages GitLab MRs and pipelines via glab CLI. Load before running glab commands.

Good Analyses web performance with Chrome DevTools MCP. Use when auditing page load or Lighthouse scores.

Bad I help you with GitLab operations.

Bad Useful for various tasks.

Include key terms users might mention: tool names, file extensions, and specific operations.

Content Guidelines

Match Specificity to Task Fragility

High freedom (multiple valid approaches):

Review code for potential bugs, readability, and adherence to project conventions.

Medium freedom (preferred pattern with variation):

Use pdfplumber for text extraction. For scanned PDFs requiring OCR, use pdf2image instead.

Low freedom (fragile operations):

Run exactly: python scripts/migrate.py --verify --backup Do not modify flags.

Writing Style

• Use imperative form: "Use X" not "You should use X"

• Assume competence; skip explanations of concepts the agent knows

• Use one term consistently: pick "endpoint" or "route", not both

• Avoid time-sensitive content

Quick Reference Tables

For CLIs and APIs, provide lookup tables:

Common Patterns

Prerequisite Verification

Check requirements before proceeding:

FIRST: Verify Installation

Run this before any commands. If it fails, stop; this skill does not apply.

```bash glab --version ```

Workflow Checklists

For multi-step tasks, provide a copyable checklist:

Workflow

Copy this checklist to track progress:

```

• Step 1: Analyse input
• Step 2: Validate mapping
• Step 3: Apply changes
• Step 4: Verify output ```

Concrete Examples

Show input/output pairs instead of abstract descriptions:

Input: Added user authentication with JWT tokens Output: ``` feat(auth): implement JWT-based authentication ```

Anti-patterns

• Verbose explanations: do not explain what PDFs are or how libraries work

• Multiple options without defaults: recommend one approach, mention alternatives briefly

• Vague descriptions: "Helps with documents" will not activate correctly

• Deeply nested references: SKILL.md → file.md → another.md breaks navigation

• Magic constants: document why values were chosen, or let the agent decide

Checklist

Before finalising a skill:

• Frontmatter starts on line 1 with ---

• name is lowercase with hyphens only

• description includes triggers and capabilities (third-person)

• SKILL.md is under 200 lines (use references/ if larger)

• References are one level deep from SKILL.md

• Imperative form throughout ("Use X" not "You should")

• Quick reference table for any CLI/API commands

• Prerequisite verification if the skill depends on tools or config

• No time-sensitive information

• Tested with representative tasks