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create-sub-agent

create-sub-agent is a skill for Claude Code, Codex from richfrem/agent-plugins-skills. It costs 55 tokens per session (659 once invoked), scanned A, original, MIT.

A guided tool for creating an autonomous sub-agent with its own instructions, permissions, and settings. It also validates the generated agent file and can place it where GitHub Copilot or Claude Code can use it.

In plain words
What is it for?
Use it to create a specialised coding agent, define when it should run, choose its tools and limits, and generate its configuration file.
Why use it?
It removes the need to design the agent format, permissions, and setup from scratch. It also checks that the resulting file follows the expected structure.

Skill for Claude CodeCodex

Part of the agent-scaffolders plugin — 33 skills, 2 plugins shipped together

not rated 6 yesterday A scan 55 tokens original MIT
View the source file richfrem/agent-plugins-skills
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/richfrem/agent-plugins-skills/create-sub-agent
Any agent
npx skills add richfrem/agent-plugins-skills --skill create-sub-agent
Clone the repo
git clone --depth 1 https://github.com/richfrem/agent-plugins-skills

Made for: Claude Code, Codex.

Or install agent-scaffolders, the plugin that ships this one along with the rest of its 33 skills, 2 plugins.

Wrote 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.

agentmods badge for create-sub-agent

README.md
[![agentmods](https://agentmods.dev/badge/skills/richfrem/agent-plugins-skills/create-sub-agent.svg)](https://agentmods.dev/skills/richfrem/agent-plugins-skills/create-sub-agent)
Your own site
<a href="https://agentmods.dev/skills/richfrem/agent-plugins-skills/create-sub-agent"><img src="https://agentmods.dev/badge/skills/richfrem/agent-plugins-skills/create-sub-agent.svg" alt="Measured on agentmods" height="20"></a>
Per session 55 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 659 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found 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 $0.00055 $0.00659
Opus 5 $0.00028 $0.00329
Sonnet 5 $0.00011 $0.00132
Haiku 4.5 $0.00006 $0.00066

Measured yesterday against content hash 3b928dd1876a, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

create-sub-agent 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 yesterday.

The scan reads SKILL.md. This mod also ships 1 executable file (references/examples/validate-agent.sh), listed below but not scanned — reading those needs a real analyzer, not pattern matching.

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.

plugins/agent-scaffolders/skills/create-sub-agent/SKILL.md · 57 lines

How it starts

The opening of the file, as written. The whole thing — 57 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Follow the create-sub-agent skill workflow to design and generate a Claude Code agent file.

Inputs

  • $ARGUMENTS — optional agent name or brief use-case description passed as initial context to the design interview. Omit to start with open discovery.

Steps

  1. If $ARGUMENTS is provided, use it as the starting context for agent name / purpose
  2. Follow the create-sub-agent phased workflow: extract core intent via design interview (purpose, input/output contract, escalation posture, tools, permissions.deny, model, maxTokens, color, lifecycle hooks, placement), present design summary, confirm, then generate the agent .md file
  3. Validate the generated agent with validate_agent.py
  4. Publication Check: Ask if the agent should be visible to GitHub Copilot or Claude Code for this repository. If yes, materialize it into .github/agents/ or .claude/agents/ and ensure the path is tracked in .gitignore.
  5. Report the created agent path, triggering conditions, and next steps

Output

Agent .md file with complete YAML frontmatter (name, description with <example> blocks, model, maxTokens, color, permissions.allowedTools, permissions.deny) and a second-person system prompt targeting 500-3,000 characters.

Placement Rules

Plugin agents: flat .md file — plugins/<plugin-name>/agents/<agent-name>.md

  • No subdirectory. Skills use skills/<name>/SKILL.md subdirectory format, but agents do NOT.
  • Confirmed against Anthropic official plugins (feature-dev, code-simplifier, hookify).

Local/project agents: .claude/agents/<agent-name>.md (also flat, no subdirectory).

Discovery & Publication

To make an agent visible to GitHub Copilot or Claude Code for this repository, follow the Discovery-First Publication pattern:

  1. Materialize the agent into .github/agents/ (Copilot) or .claude/agents/ (Claude).
  2. Ensure .gitignore allows the specific agent file or subdirectory.
  3. Commit the materialized file to the repository.

Read the full file on GitHub · 57 lines

Files

What ships with it

60 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. yesterday First seen · 57 lines · 55 tokens per session scan A 3b928dd1876a

Subscribe to this mod's changes

create-sub-agent is a skill published in the GitHub repository richfrem/agent-plugins-skills (6 stars, last pushed yesterday), licensed MIT. It adds 55 tokens to every session and 659 once invoked, about $0.0003 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.

Building agentsagent-skillsagentic-frameworkagentic-harnessagentic-osclaude-code-skillclaude-plugins
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