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.
npx skills add majiayu000/claude-skill-registry --skill agent-builder-majiayu000-claude-skill-registr-86e748e2git clone --depth 1 https://github.com/majiayu000/claude-skill-registryWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/majiayu000/claude-skill-registry/agent-builder-majiayu000-claude-skill-registr-86e748e2)<a href="https://agentmods.dev/skills/majiayu000/claude-skill-registry/agent-builder-majiayu000-claude-skill-registr-86e748e2"><img src="https://agentmods.dev/badge/skills/majiayu000/claude-skill-registry/agent-builder-majiayu000-claude-skill-registr-86e748e2/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/skills/majiayu000/claude-skill-registry/agent-builder-majiayu000-claude-skill-registr-86e748e2"><img src="https://agentmods.dev/badge/skills/majiayu000/claude-skill-registry/agent-builder-majiayu000-claude-skill-registr-86e748e2.svg" alt="Reviewed on agentmods" width="80" height="20"></a>- NVIDIA SkillSpector warn
SkillSpector: 2 findings, up to high
These are SkillSpector’s own severities. On a checked sample its high-severity flags on skills were ~96% false positives — a documented command, a public API, a “never do X” rule — so we show them as a caution to read, not a verdict. Why →
- high Data Exfiltration · line 373 Code or instructions that leak agent conversation context to external services, potentially exposing sensitive user interactions.Fix: Remove any code that sends prompts, responses, or session data externally. Preserve user privacy; never exfiltrate conversation content.
- medium Rogue Agent · line 13 Skill establishes unauthorized persistence across sessions via cron jobs, startup scripts, or state files. Session persistence allows an attacker to maintain access beyond the current interaction.Fix: Remove any persistence mechanisms (cron jobs, startup scripts, state files). Skills should not maintain state across sessions without explicit user consent.
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.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00040 | $0.04868 |
| Opus 5 | $0.00020 | $0.02434 |
| Sonnet 5 | $0.00008 | $0.00974 |
| Haiku 4.5 | $0.00004 | $0.00487 |
Grade A, and why
agent-builder 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 9d 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.
Copies of this mod
3 near-identical copies found in the catalogue:
- agent-builder — 100% identical, 0 lines differ
- agent-builder — 100% identical, 0 lines differ
- agent-builder — 97% identical, 5 lines differ
How it starts
The opening of the file, as written. The whole thing — 916 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Agent Builder - Claude Code Subagent Expert
Use this skill when creating, improving, or troubleshooting Claude Code subagents. Provides expert guidance on agent design, system prompt engineering, tool configuration, and delegation patterns.
When to Use This Skill
Activate this skill when:
- User asks to create a new subagent
- User wants to improve an existing agent
- User needs help with agent configuration or tool access
- User is troubleshooting agent invocation issues
- User wants to understand when to use agents vs skills vs commands
- User asks about agent chaining or delegation patterns
Quick Reference
Agent File Structure
---
name: agent-name
description: When and why to use this agent
tools: Read, Write, Bash(git *)
model: sonnet
---
Your detailed system prompt defining:
- Agent role and expertise
- Problem-solving approach
- Output format expectations
- Specific constraints or requirements
File Locations
Project agents (shared with team, highest priority):
.claude/agents/my-agent.md
Personal agents (individual use, lower priority):
~/.claude/agents/my-agent.md
Plugin agents (from installed plugins):
<plugin-dir>/agents/agent-name.md
Creating Effective Subagents
Step 1: Identify the Use Case
Good candidates for subagents:
- Complex, multi-step workflows
- Specialized expertise (debugging, security review, data analysis)
- Tasks requiring focused context
- Repeatable processes with specific quality bars
- Code review and analysis workflows
NOT good for subagents (use Skills/Commands instead):
- Simple one-off prompts (use Slash Commands)
- Context-aware automatic activation (use Skills)
- Quick transformations or formatting
Step 2: Design Agent Scope
Best practices:
- Single responsibility - Each agent does ONE thing exceptionally well
- Clear boundaries - Define what's in/out of scope
- Specific expertise - Don't create "general helper" agents
- Measurable outcomes - Agent should produce concrete deliverables
What ships with it
1 file 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.
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.
- 9d ago First seen · 916 lines · 40 tokens per session scan A 6327d28daa03
agent-builder is a skill published in the GitHub repository majiayu000/claude-skill-registry (604 stars, last pushed yesterday), licensed MIT. It adds 40 tokens to every session and 4,868 once invoked, about $0.0002 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-09-03.
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