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/practicalswan/agent-skills/custom-agent-usagenpx skills add PracticalSwan/agent-skills --skill custom-agent-usagegit clone --depth 1 https://github.com/PracticalSwan/agent-skillsWrote 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/practicalswan/agent-skills/custom-agent-usage)<a href="https://agentmods.dev/skills/practicalswan/agent-skills/custom-agent-usage"><img src="https://agentmods.dev/badge/skills/practicalswan/agent-skills/custom-agent-usage.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 | $0.00054 | $0.01630 |
| Opus 5 | $0.00027 | $0.00815 |
| Sonnet 5 | $0.00011 | $0.00326 |
| Haiku 4.5 | $0.00005 | $0.00163 |
Grade A, and why
custom-agent-usage 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 — 174 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Custom Agent Usage
- Leverage native parallel subagent dispatch and 200k+ context windows where available.
Activation Conditions
Use symptom -> action triggers: when one matches, apply this skill and verify with the protocol below.
Activate this skill when:
- Discovering available custom agents from the local Claude or VS Code Insiders agent directories
- Understanding
.agent.mdfile structure and frontmatter - Checking if an agent can be invoked as a subagent
- Learning which
agentNameto use for delegation - Understanding agent tools and capabilities
Custom Agent Discovery
Custom agents for this environment are discovered from these directories:
- Claude agents:
C:\Users\LOQ\.claude\agents - VS Code Insiders prompts:
C:\Users\LOQ\AppData\Roaming\Code - Insiders\User\prompts
Notes:
- Filter to
*.agent.mdwhen discovering subagents. - The VS Code Insiders prompts directory can also contain
.prompt.mdand.instructions.mdfiles that are not subagents.
To discover agents:
- Search for
*.agent.mdfiles in the configured Claude and VS Code Insiders directories. - Read frontmatter of each agent file to understand capabilities.
- Ignore
.prompt.mdand.instructions.mdfiles when the goal is subagent delegation.
Agent Frontmatter
Key frontmatter fields in .agent.md:
| Field | Purpose | Required? |
|---|---|---|
name |
Display name used in agentName parameter |
Recommended |
description |
What the agent specializes in | Recommended |
tools |
Tools available to the agent | Optional |
disable-model-invocation |
If false, agent can be invoked as subagent | Required |
Invocability Check
CRITICAL: Only agents with disable-model-invocation: false in frontmatter can be invoked as subagents.
Check frontmatter:
---
name: "Code Explainer"
description: For analyzing and documenting existing code
disable-model-invocation: false # Must be false for subagent delegation
tools: [Read, Search]
---
What ships with it
5 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.
- yesterday Changed 464bc56e9413
- 4d ago First seen · 174 lines · 54 tokens per session scan A 3aac4e084610
custom-agent-usage is a skill published in the GitHub repository PracticalSwan/agent-skills (13 stars, last pushed 4d ago), licensed MIT. It adds 54 tokens to every session and 1,630 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 2026-08-30.
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