# Custom Agent Usage

> Discover, validate, and invoke .agent.md custom agents. Use when finding agent files in the local Claude or VS Code Insiders directories, checking frontmatter, verifying disable-model-invocation, or determining agentName for runSubagent calls.

- Skill: `practicalswan/custom-agent-usage` (Agent Skill, multi-file: 6 files)
- Install (CLI): `npx skillmds add practicalswan/custom-agent-usage`
- Raw SKILL.md: https://api.skillmd.com/api/skills/practicalswan/custom-agent-usage/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: AI & ML
- Author: practicalswan (https://skillmd.com/u/practicalswan)
- Updated: 2026-09-09
- Page: https://skillmd.com/skills/practicalswan/custom-agent-usage

---

# 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.md` file structure and frontmatter
- Checking if an agent can be invoked as a subagent
- Learning which `agentName` to 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.md` when discovering subagents.
- The VS Code Insiders prompts directory can also contain `.prompt.md` and `.instructions.md` files that are not subagents.

**To discover agents:**
1. Search for `*.agent.md` files in the configured Claude and VS Code Insiders directories.
2. Read frontmatter of each agent file to understand capabilities.
3. Ignore `.prompt.md` and `.instructions.md` files 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:
```yaml
---
name: "Code Explainer"
description: For analyzing and documenting existing code
disable-model-invocation: false  # Must be false for subagent delegation
tools: [Read, Search]
---
```

## Using Custom Agents

### Step 1: Discover Available Agents

Search the real agent directories and keep only `*.agent.md` files:
```powershell
Get-ChildItem `
  'C:\Users\LOQ\.claude\agents', `
  'C:\Users\LOQ\AppData\Roaming\Code - Insiders\User\prompts' `
  -Filter *.agent.md `
  -File
```

Or use the helper script:
```powershell
node .\scripts\agent-finder.js
```

### Step 2: Check Invocability

Verify `disable-model-invocation: false` is set.

### Step 3: Get Agent Name

Use the `name` field from frontmatter exactly as is.
- If frontmatter has `name` field value, use that value in quotes.
- If name is not specified, use the filename without the `.agent.md` extension.

### Step 4: Delegate Task

```javascript
runSubagent({
  agentName: "Playwright Tester Mode",  // Must match 'name' from frontmatter exactly
  description: "Test checkout flow",
  prompt: "Perform exploratory testing on the checkout flow: product selection -> cart -> payment confirmation. Generate comprehensive Playwright tests covering success scenarios, validation errors, edge cases (empty cart, payment failures), and accessibility."
})
```

<!-- MCP:START -->

<!-- PORTABILITY:START -->
## Cross-Client Portability

This skill is written to stay usable across GitHub Copilot, Claude Code, and Codex.

- GitHub Copilot: keep the folder in a Copilot-visible skill path or wrap the
  workflow in project instructions when folder discovery is unavailable.
- Claude Code: keep the folder in a local skills directory or a compatible plugin source.
- Codex: install or sync the folder into
  `$CODEX_HOME/skills/custom-agent-usage` and restart Codex after major changes.

<!-- PORTABILITY:END -->

## MCP Availability And Fallback

Preferred MCP Server: None required

- Fallback prompt: "Use the Custom Agent Usage skill without MCP. Rely on its local instructions, bundled resources, standard shell or editor tools, and direct verification. Show the evidence used before concluding."
- Do not claim an MCP operation was used when the active host does not expose it.
- Treat local files, tests, rendered outputs, logs, or screenshots as the fallback evidence path.

<!-- MCP:END -->

## Anti-Patterns

- Delegating or evaluating without a scoped success condition: The output becomes hard to review and easy to overbuild.
- Skipping the evidence step: A workflow that cannot be re-checked quickly is not ready for handoff.
- Bundling unrelated subtasks together: It creates noisy prompts, weaker ownership, and avoidable integration risk.

## Verification Protocol

Before claiming "skill applied successfully":

1. Pass/fail: The Custom Agent Usage workflow names the agent boundary, delegated scope, and expected return artifact.
2. Pass/fail: Context passed to helpers is minimal, task-local, and free of hidden expected answers.
3. Pass/fail: Results are integrated only after evidence, diffs, or citations are checked by the controller.
4. Pressure-test scenario: Run the workflow on two similar tasks that must not share assumptions or leaked context.
5. Success metric: Zero context leakage; every delegated output is independently reviewable.

## Workflow Example

```javascript
// Step 1: Main agent analyzes task and identifies need for testing
// "I need comprehensive testing for the checkout flow"

// Step 2: Discover custom testing agent
// Found: C:\Users\LOQ\.claude\agents\playwright-tester.agent.md
// disable-model-invocation: false and name: "Playwright Tester Mode"

// Step 3: Delegate to custom agent
runSubagent({
  agentName: "Playwright Tester Mode",
  description: "Test checkout flow",
  prompt: "Perform exploratory testing on the checkout flow: product selection -> cart -> payment confirmation. Generate comprehensive Playwright tests covering success scenarios, validation errors, edge cases (empty cart, payment failures), and accessibility."
})

// Step 4: Review test output and integrate into test suite
```

## Examples & Scripts

- [Agent Discovery Workflow](./examples/agent-discovery-workflow.md) - Examples of finding and using custom agents
- [Agent Finder Script](./scripts/agent-finder.js) - Node.js script to discover and inspect custom agents

## Related Skills

- [agent-task-mapping](../agent-task-mapping/SKILL.md): Use it when the workflow also needs task-to-agent routing decisions.
- [subagent-delegation](../subagent-delegation/SKILL.md): Use it when the workflow also needs safe, scoped delegation to helper agents.
- [subagent-driven-development](../subagent-driven-development/SKILL.md): Use it when the workflow also needs plan-driven implementation with reviewer loops.
- [agentic-eval](../agentic-eval/SKILL.md): Use it when the workflow also needs rubric-driven evaluation loops.