Borrowing it
Nothing to install: this file belongs to houarnu166/skillful-agent-system-builder. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.
curl -O https://raw.githubusercontent.com/houarnu166/skillful-agent-system-builder/main/.agents/skills/agent-design/SKILL.mdgit clone --depth 1 https://github.com/houarnu166/skillful-agent-system-builderWrote 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/houarnu166/skillful-agent-system-builder/agent-design)<a href="https://agentmods.dev/skills/houarnu166/skillful-agent-system-builder/agent-design"><img src="https://agentmods.dev/badge/skills/houarnu166/skillful-agent-system-builder/agent-design.svg" alt="Measured on agentmods" height="20"></a>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 | $0.00074 | $0.00543 |
| Opus 5 | $0.00037 | $0.00271 |
| Sonnet 5 | $0.00015 | $0.00109 |
| Haiku 4.5 | $0.00007 | $0.00054 |
Grade A, and why
agent-design 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 7d 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.
What it actually says
Agent Design Guide
Required Frontmatter Fields
| Field | Format | Rules |
|---|---|---|
name |
lowercase + hyphens | 1-64 chars, no reserved words |
description |
text | 1-1024 chars, role + trigger conditions |
tools |
array | least privilege principle |
→ See frontmatter-fields.md for detailed rules
Tool Selection Guide
| Pattern | Tools | Purpose |
|---|---|---|
| Read-only | Read, Grep, Glob, Bash |
Exploration/Analysis |
| Writer | Read, Write, Edit, Bash |
File modification |
| Interactive | Read, AskUserQuestion |
User questions |
| Orchestrator | Read, Write, Task |
Subagent coordination |
→ See tool-selection.md for detailed patterns
Model Selection
| Model | Use Case | Cost |
|---|---|---|
haiku |
Fast exploration, simple tasks | ~$0.25/MTok |
sonnet |
Balanced choice (default) | ~$3/MTok |
opus |
Complex reasoning | ~$15/MTok |
System Prompt Structure
You are {name}, a {specialist type}.
## Your Role
{detailed role description}
## Process
### Step 1: {step name}
{description}
## Output Format
{expected output format}
## Important Notes
- {cautions}
→ See examples.md for complete Agent examples
Design Principles
- Single Responsibility: Each Agent has one clear role
- Clear Triggers: Specify usage timing in description
- Least Privilege: Grant only necessary tools
- Specific Process: Define step-by-step tasks clearly
Common Mistakes
- ❌ Missing trigger conditions in description
- ❌ Excessive permission grants (listing all tools)
- ❌ Vague role definition
- ❌ Skipping process steps
- ❌ Giving Task tool to Worker Agents
What ships with it
3 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.
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.
- 7d ago First seen · 76 lines · 74 tokens per session scan A 26ae77c76aa0
agent-design is a skill published in the GitHub repository houarnu166/skillful-agent-system-builder (23 stars, last pushed 7mo ago), licensed MIT. It adds 74 tokens to every session and 543 once invoked, about $0.0004 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 2026-08-30.
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