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 agentmods add skills/laurigates/claude-plugins/custom-agent-definitionsnpx skills add laurigates/claude-plugins --skill custom-agent-definitionsgit clone --depth 1 https://github.com/laurigates/claude-pluginsWrote 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/laurigates/claude-plugins/custom-agent-definitions)<a href="https://agentmods.dev/skills/laurigates/claude-plugins/custom-agent-definitions"><img src="https://agentmods.dev/badge/skills/laurigates/claude-plugins/custom-agent-definitions.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 | $0.00037 | $0.01806 |
| Opus 5 | $0.00018 | $0.00903 |
| Sonnet 5 | $0.00007 | $0.00361 |
| Haiku 4.5 | $0.00004 | $0.00181 |
Grade A, and why
custom-agent-definitions 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.
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.
How it starts
The opening of the file, as written. The whole thing — 162 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Custom Agent Definitions
Expert knowledge for defining and configuring custom agents in Claude Code.
For full worked YAML examples (isolated research agent, read-only explorer, complete security auditor, plugin layout, common patterns), see REFERENCE.md.
When to Use This Skill
| Use this skill when... | Use agent-teams instead when... |
|---|---|
Authoring a new .md agent definition file in .claude/agents/ |
Spawning multiple already-defined agents that coordinate as a team |
Configuring a single agent's model, allowed-tools, or context: fork |
Setting up a lead/teammate architecture with a shared task list |
| Constraining tool access for a specialised read-only or write-restricted agent | Sequencing parallel work across worktrees (see parallel-agent-dispatch) |
| Writing the system prompt that defines what one agent does | Auditing existing agent definitions for security (see meta-audit) |
Core Concepts
Custom agents let you define specialized agent types beyond the built-in
ones (Explore, Plan, Bash, etc.). Each can have its own model, tools, and
context configuration. They are defined in .claude/agents/ or via plugin
agents/ directories, with YAML frontmatter + a markdown system prompt:
---
name: my-custom-agent
description: What this agent does
model: sonnet
allowed-tools: Bash, Read, Grep, Glob
---
# Agent System Prompt
Instructions and context for the agent...
Key Fields
Context Forking
| Value | Behavior |
|---|---|
fork |
Independent context copy — agent sees parent history but changes don't affect parent |
| (default) | Agent shares context with parent and can see/modify conversation state |
Use fork for exploratory research, parallel investigations, and isolated
experiments. See REFERENCE.md → Isolated research agent.
Tool Access (allowed vs disallowed)
| Field | Purpose | Behavior |
|---|---|---|
allowed-tools |
Whitelist of permitted tools | Agent can ONLY use these tools |
disallowedTools |
Blacklist of forbidden tools | Agent can use all tools EXCEPT these |
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.
- yesterday Changed · +7 lines 1a191c2f2d43
- 5d ago First seen · 155 lines · 37 tokens per session scan A 06dab1ee1567
custom-agent-definitions is a skill published in the GitHub repository laurigates/claude-plugins (58 stars, last pushed today), licensed MIT. It adds 37 tokens to every session and 1,806 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 2026-08-30.
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