# Subagent Prompting

> Template for structured sub-agent invocation using 4-part prompting (GOAL/CONSTRAINTS/CONTEXT/OUTPUT) and F# pipeline notation. Use when orchestrating sub-agents or designing multi-agent workflows.

- **Type:** Skill
- **Install:** `agentstack add skill-ashaykubal-essential-agents-skills-subagent-prompting`
- **Verified:** Yes — security-reviewed for prompt injection and unsafe behavior
- **Seller:** [ashaykubal](https://agentstack.voostack.com/s/ashaykubal)
- **Installs:** 0
- **Category:** [Agent Skills](https://agentstack.voostack.com/c/agent-skills)
- **Latest version:** 0.1.0
- **License:** MIT
- **Upstream author:** [ashaykubal](https://github.com/ashaykubal)
- **Source:** https://github.com/ashaykubal/essential-agents-skills/tree/master/skills/subagent-prompting

## Install

```sh
agentstack add skill-ashaykubal-essential-agents-skills-subagent-prompting
```

Requires the [AgentStack CLI](https://agentstack.voostack.com/docs/cli). Works with Claude Code, Cursor, and any MCP-compatible agent.

## About

# Sub-Agent Prompting Template

## Overview

This skill provides a standardized template for invoking sub-agents with deterministic inputs and predictable outputs. Use this when:

- Orchestrating specialist sub-agents (code auditor, test auditor, etc.)
- Designing multi-agent workflows with conditional branching
- Ensuring consistent prompt structure across sub-agent invocations

## 4-Part Template (Required)

Every sub-agent invocation MUST include all four parts. Incomplete prompts lead to unpredictable behavior.

### GOAL (What Success Looks Like)

State the high-level objective, not just the action. Good goals are outcome-focused.

```markdown
## GOAL

[Describe the desired end state, not the process]

Examples:
- GOOD: "Identify all security vulnerabilities that could allow unauthorized data access"
- BAD: "Review the auth file"

- GOOD: "Refactor authentication module for improved maintainability without breaking existing tests"
- BAD: "Refactor the code"
```

### CONSTRAINTS (What You Cannot Do)

Explicit boundaries prevent scope creep and unexpected changes.

```markdown
## CONSTRAINTS

- [Hard limit 1: e.g., "Do NOT modify any files"]
- [Hard limit 2: e.g., "Do NOT add new dependencies"]
- [Hard limit 3: e.g., "Maintain backward API compatibility"]
- [Resource limit: e.g., "Complete within 50 tool calls"]

Examples:
- "Identify issues only - do NOT implement fixes"
- "Read-only analysis - no file modifications"
- "Focus only on files in src/auth/ directory"
```

### CONTEXT (What You Need to Know)

Provide all information required to complete the task. Sub-agents run in isolated context and cannot access parent conversation.

```markdown
## CONTEXT

### Files to Analyze
- `path/to/file1.ts` - [brief description of relevance]
- `path/to/file2.ts` - [brief description of relevance]

### Related Context
- Previous findings: [summary of relevant prior work]
- Architecture notes: [relevant design decisions]
- Known issues: [existing problems to be aware of]

### Standards to Apply
- [Coding standard or guideline reference]
- [Security policy reference if applicable]
```

### OUTPUT (What to Deliver)

Specify concrete deliverables with exact format requirements.

```markdown
## OUTPUT

### Primary Deliverable
Write findings to: `logs/{agent-name}-{timestamp}.md`

### Output Format
[Specify structure: YAML, Markdown sections, etc.]

### Summary Requirements
Return to main thread: [max 200 tokens summary of key findings]

### Diagnostic Output
Write to: `logs/diagnostics/{agent-name}-{timestamp}.yaml`
```

---

## Pipeline Syntax (F# Conceptual Notation)

### Understanding the Notation

F# pipe syntax (`|>`) is a **conceptual notation** for planning and documentation. It is NOT directly executable Claude Code syntax.

```fsharp
// This is documentation, not executable code
Agent1 (task) |> Agent2 (task) |> Agent3 (task)
```

**Purpose**: Visualize workflow dependencies and conditional logic before implementation.

### Mapping to Task() Invocations

Each pipeline stage maps to a sequential `Task()` call from the main thread:

```fsharp
// Conceptual pipeline
CodeAuditor (security) |> CodeAuditor (architecture) |> (if findings > 0 then IssueDebugger else Done)
```

**Actual execution**:

1. Main thread invokes: `Task(description="Security audit", subagent_type="sonnet", prompt="[4-part prompt]")`
2. Main thread reads log output, extracts findings
3. Main thread invokes: `Task(description="Architecture audit", subagent_type="sonnet", prompt="[4-part prompt]")`
4. Main thread reads log output, extracts findings
5. IF `findings.count > 0`: Main thread invokes IssueDebugger
6. ELSE: Pipeline complete

### Pipeline Patterns

**Code Review Pipeline:**
```fsharp
CodeAuditor (security)
|> CodeAuditor (architecture)
|> TestAuditor (coverage)
|> (if findings > 0 then IssueDebugger else Done)
```

**Fix Validation Pipeline:**
```fsharp
IssueDebugger (root cause)
|> Implementer (apply fix)
|> CodeAuditor (verify quality)
|> TestAuditor (verify tests)
|> (if issues > 0 then IssueDebugger else Done)  // Loop until clean
```

**Test Audit Pipeline:**
```fsharp
TestAuditor (classify all)
|> (if mock_heavy > 0 then VerificationScriptCreator else Done)
|> Implementer (rewrite flagged)
|> TestAuditor (re-verify)
```

### Key Constraint

Sub-agents CANNOT spawn other sub-agents. All pipeline orchestration happens from the main thread.

---

## Custom Agent vs Built-in Agent

### Agent Selection Priority

Before spawning a pipeline stage:

1. **Check `.claude/agents/`** for a custom agent matching the task
2. **If custom agent exists**: Use its `name` field as `subagent_type` - this invokes the custom agent
3. **If no custom agent**: Use `general-purpose` and provide full specialized instructions in the prompt

### Important: 4-Part Prompt Always Required

Regardless of agent type, every Task invocation MUST include the 4-part prompt (GOAL/CONSTRAINTS/CONTEXT/OUTPUT) and follow subagent-output-templating for output format.

### Built-in Agent Types

| Type | Use Case |
|------|----------|
| `general-purpose` | Multi-step tasks, code writing, analysis |
| `Explore` | Fast codebase exploration, file search |
| `Plan` | Architecture planning, implementation design |
| `Bash` | Command execution |

### Example: Custom Agent EXISTS

```python
# .claude/agents/security-auditor.md exists with name: security-auditor
Task(
    description="Security audit",
    subagent_type="security-auditor",  # Invokes the custom agent
    prompt="""
## GOAL
Identify security vulnerabilities in calculator.ts

## CONSTRAINTS
- Do NOT modify files

## CONTEXT
File: src/calculator.ts

## OUTPUT
Write to: logs/security-audit-{timestamp}.yaml
"""
)
```

### Example: Custom Agent DOES NOT Exist

```python
# No custom agent for this task - use general-purpose
Task(
    description="Security audit",
    subagent_type="general-purpose",
    model="sonnet",
    prompt="""
## GOAL
Identify security vulnerabilities in calculator.ts using OWASP Top 10 patterns.

## CONSTRAINTS
- Do NOT modify files
- Focus on injection, auth, and data exposure risks

## CONTEXT
File: src/calculator.ts
This is a calculator module with arithmetic operations.

## OUTPUT
Write findings to: logs/security-audit-{timestamp}.yaml
Format: YAML with findings array, severity, and recommendations
"""
)
```

Note: When no custom agent exists, the prompt must include all specialized instructions that would otherwise be in the custom agent's markdown file.

---

## Model Selection Guidance

### Task-Type Based Selection (Objective)

Model selection is based on **task type**, not subjective complexity. This keeps selection deterministic and objective.

| Model | Task Type | Examples |
|-------|-----------|----------|
| **Haiku** | Lookups & Execution | Web fetch, file read/summarize, collect logs, run tests, typecheck, lint, simple classification |
| **Sonnet** | Review & Analysis | Code review, test review, audits, failure analysis, security analysis |
| **Opus** | Write & Fix | Write code, write tests, write fixes, apply changes |

### Selection Rules

1. **Determine task type from the action verb**:
   - Lookup/Execute/Run/Fetch → **Haiku**
   - Review/Analyze/Audit/Classify → **Sonnet**
   - Write/Fix/Implement/Apply → **Opus**

2. **Custom agent override**: If a custom sub-agent has `agent:` in its frontmatter, use that model instead of these rules.

3. **Always specify model**: Every Task() invocation must include `subagent_type`.

### Pipeline Example

```
Orchestrator (Opus) writes initial code
     ↓
Sub-agent (Sonnet) reviews → finds issues
     ↓
Sub-agent (Opus) fixes
     ↓
Sub-agent (Sonnet) re-reviews
     ↓
[Loop until clean]
```

### Anti-Patterns

| Anti-Pattern | Why It's Wrong | Correct Approach |
|--------------|----------------|------------------|
| Using Opus for lookups | Wastes budget on simple tasks | Use Haiku for lookups |
| Using Haiku for code review | Misses nuanced issues | Use Sonnet for analysis |
| Using Sonnet for writing fixes | Suboptimal quality | Use Opus for writing |
| No model specified | Unpredictable behavior | Always specify `subagent_type` |
| Ignoring custom agent frontmatter | Overrides intended behavior | Respect `agent:` field |

---

## Diagnostic Output (Required)

When this skill is used to invoke a sub-agent, the sub-agent MUST write diagnostic output.

### Diagnostic File Location

```
logs/diagnostics/{skill-name}-{YYYYMMDD-HHMMSS}.yaml
```

### Diagnostic Format

```yaml
skill: subagent-prompting
timestamp: 2026-01-10T12:30:45Z
diagnostics:
  model_requested: sonnet
  model_actual: sonnet
  context_type: main
  parent_vars_accessible: true
  hooks_fired: []
  execution_time_ms: 1250
  completion_status: success
notes: "Skill invoked successfully"
```

### When to Write Diagnostics

- At the END of skill execution (success or failure)
- Include actual model used (may differ from requested)
- Record execution time for performance tracking

---

## Quick Reference

### Prompt Checklist

```markdown
[ ] GOAL: Outcome-focused objective stated
[ ] CONSTRAINTS: Hard limits explicitly listed
[ ] CONTEXT: All required files and background provided
[ ] OUTPUT: Log path, format, and summary requirements specified
[ ] DIAGNOSTIC: logs/diagnostics/ path included
```

### Task() Invocation Template

```python
Task(
    description="[3-5 word summary]",
    subagent_type="sonnet",  # or "haiku", "opus"
    prompt="""
## GOAL
[Outcome-focused objective]

## CONSTRAINTS
- [Limit 1]
- [Limit 2]

## CONTEXT
[Files, background, standards]

## OUTPUT
Write to: logs/{agent}-{timestamp}.md
Diagnostic: logs/diagnostics/{agent}-{timestamp}.yaml
Summary: [max 200 tokens]
"""
)
```

---

## References

For extended examples and edge cases, see `references/examples.md`.

## Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

- **Author:** [ashaykubal](https://github.com/ashaykubal)
- **Source:** [ashaykubal/essential-agents-skills](https://github.com/ashaykubal/essential-agents-skills)
- **License:** MIT

Install and usage instructions live in the source repository linked above.

## Pricing

- **Free** — Free

## Security capabilities

Automated source analysis of v0.1.0 — what this tool can access:

- **Network access:** no
- **Filesystem access:** no
- **Shell / process execution:** no
- **Environment & secrets:** no
- **Dynamic code execution:** no

*"Yes" means the capability is present in the source — more access means more to trust, not that it is unsafe.*


## Versions

- **0.1.0** — security scan: passed — Imported from the upstream source.

## Links

- Listing page: https://agentstack.voostack.com/l/skill-ashaykubal-essential-agents-skills-subagent-prompting
- Seller: https://agentstack.voostack.com/s/ashaykubal
- Browse the marketplace: https://agentstack.voostack.com/browse

---
Listed on AgentStack — the marketplace for AI agent skills and MCP servers. Every listing is security-reviewed. Creators keep 70%.