skill-developer

A guide for creating and managing Claude Code skills, including their structure, activation rules, and supporting hooks.

In plain words
What is it for?
Use it to create skills, change activation triggers, work with skill rules and hooks, or debug why a skill does or does not activate.
Why use it?
It helps keep skills focused, discoverable, and activated for the right kinds of requests.

Skill for Claude CodeCodex

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add skills/wislertt/bakefile/skill-developer
Any agent
npx skills add wislertt/bakefile --skill skill-developer
Clone the repo
git clone --depth 1 https://github.com/wislertt/bakefile

Made for: Claude Code, Codex.

Per session 97 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 2,914 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin 86% copy Near-identical to another mod in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00097 $0.02914
Opus 5 $0.00048 $0.01457
Sonnet 5 $0.00019 $0.00583
Haiku 4.5 $0.00010 $0.00291

Measured 2d ago against content hash 09d1ab73335a, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

skill-developer scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

Origin

This is a copy

86% identical to skill-developer — 119 lines differ, which has more behind it and is treated as the original. This page carries a canonical link to it rather than competing with it.

.claude/skills/skill-developer/SKILL.md · 466 lines

How it starts

The opening of the file, as written. The whole thing — 466 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Skill Developer Guide

Purpose

Comprehensive guide for creating and managing skills in Claude Code with auto-activation system, following Anthropic's official best practices including the 500-line rule and progressive disclosure pattern.

When to Use This Skill

Automatically activates when you mention:

  • Creating or adding skills
  • Modifying skill triggers or rules
  • Understanding how skill activation works
  • Debugging skill activation issues
  • Working with skill-rules.json
  • Hook system mechanics
  • Claude Code best practices
  • Progressive disclosure
  • YAML frontmatter
  • 500-line rule

System Overview

Two-Hook Architecture

1. UserPromptSubmit Hook (Proactive Suggestions)

  • File: .claude/hooks/skill-activation-prompt.ts
  • Trigger: BEFORE Claude sees user's prompt
  • Purpose: Suggest relevant skills based on keywords + intent patterns
  • Method: Injects formatted reminder as context (stdout → Claude's input)
  • Use Cases: Topic-based skills, implicit work detection

2. Stop Hook - Error Handling Reminder (Gentle Reminders)

  • File: .claude/hooks/error-handling-reminder.ts
  • Trigger: AFTER Claude finishes responding
  • Purpose: Gentle reminder to self-assess error handling in code written
  • Method: Analyzes edited files for risky patterns, displays reminder if needed
  • Use Cases: Error handling awareness without blocking friction

Philosophy Change (2025-10-27): We moved away from blocking PreToolUse for Sentry/error handling. Instead, use gentle post-response reminders that don't block workflow but maintain code quality awareness.

Configuration File

Location: .claude/skills/skill-rules.json

Defines:

  • All skills and their trigger conditions
  • Enforcement levels (block, suggest, warn)
  • File path patterns (glob)
  • Content detection patterns (regex)
  • Skip conditions (session tracking, file markers, env vars)

Skill Types

1. Guardrail Skills

Purpose: Enforce critical best practices that prevent errors

Read the full file on GitHub · 466 lines

Files

What ships with it

6 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 2d ago First seen · 466 lines · 97 tokens per session scan A 09d1ab73335a

Subscribe to this mod's changes

skill-developer is a skill published in the GitHub repository wislertt/bakefile (5 stars, last pushed 4d ago), licensed Apache-2.0. It adds 97 tokens to every session and 2,914 once invoked, about $0.0005 per session on Opus 5. A static security scan graded it A with 0 findings. It is 86% identical to skill-developer, differing in 119 lines, and is treated as a copy.

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