pi-subagent

Agent Building

Delegate tasks to specialized subagents for parallel or sequential execution.

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How to use this skill

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Source SKILL.md: https://github.com/espennilsen/pi/blob/HEAD/extensions/pi-subagent/skills/pi-subagent/SKILL.md

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Subagent Orchestration

Use the subagent tool to delegate tasks to isolated pi subprocesses. Each subagent gets a fresh context window — no shared state with the parent session.

When to use subagents

A task can be split into independent pieces that run in parallel
You need a chain of specialists (scout → planner → worker)
A subtask benefits from a clean context window (no accumulated noise)
You want crash isolation (failed subtask doesn't corrupt main session)

Modes

Single — one agent, one task

{ "agent": "scout", "task": "Find all REST endpoints in src/" }

Parallel — multiple agents concurrently (streams progress as each completes)

{ "tasks": [
    { "agent": "scout", "task": "Audit auth module" },
    { "agent": "scout", "task": "Audit API routes" },
    { "agent": "scout", "task": "Audit database queries" }
  ]
}

Chain — sequential pipeline, use `{previous}` for prior step's output

{ "chain": [
    { "agent": "scout", "task": "Find all TODO comments in the codebase" },
    { "agent": "planner", "task": "Categorize and prioritize these TODOs:\n{previous}" },
    { "agent": "worker", "task": "Fix the top 3 critical TODOs:\n{previous}" }
  ]
}

Per-task options

Every task (single, parallel item, chain step) supports these overrides:

Option	Type	Description
`model`	string	Model override (e.g. `"claude-haiku-4-5"` for fast, `"claude-sonnet-4-5"` for complex)
`thinking`	string	Thinking level: `off`, `minimal`, `low`, `medium`, `high`, `xhigh`
`extensions`	string[]	Extension paths to load (subagents run with `-ne` — only whitelisted)
`skills`	string[]	Skill files/dirs to load via `--skill`
`noTools`	boolean	Disable all built-in tools (`--no-tools`) — for analysis-only agents
`noSkills`	boolean	Disable skill discovery (`-ns`)
`cwd`	string	Working directory override

Priority: per-task item > top-level params > agent .md frontmatter > global settings

Examples

Fast recon with cheap model, no thinking overhead:

{ "agent": "scout", "task": "Map the auth module", "model": "claude-haiku-4-5", "thinking": "off" }

Research task needing web search:

{ "agent": "worker", "task": "Find pricing for Vercel Pro", "extensions": ["extensions/pi-brave-search"] }

Parallel with different models per task:

{ "tasks": [
    { "agent": "scout", "task": "Map the codebase", "model": "claude-haiku-4-5" },
    { "agent": "reviewer", "task": "Review the PR diff", "model": "claude-sonnet-4-5", "thinking": "high" }
  ]
}

Chain with escalating capability:

{ "chain": [
    { "agent": "scout", "task": "Map the auth module", "model": "claude-haiku-4-5", "thinking": "off" },
    { "agent": "planner", "task": "Plan a refactor based on: {previous}", "thinking": "high" },
    { "agent": "worker", "task": "Implement the plan: {previous}", "thinking": "medium" }
  ]
}

Extension isolation

Subagents always run with --no-extensions (-ne). They cannot:

Spawn further subagents (pi-subagent is always blocked)
Send messages via channels, cron, or heartbeat
Access the web dashboard or webserver

Whitelist only what a specific task needs via the extensions parameter.

Agent scope

"user" (default) — loads from ~/.pi/agent/agents/*.md
"both" — also includes .pi/agents/*.md (prompts for confirmation)
"project" — only project-local agents

Creating agents

Place .md files in ~/.pi/agent/agents/ with YAML frontmatter:

---
name: scout
description: Fast codebase reconnaissance
tools: read, grep, find, ls, bash
extensions: extensions/pi-dotenv
model: claude-haiku-4-5
---
System prompt for the agent goes here...

Frontmatter	Description
`name`	Agent name (required)
`description`	What the agent does (required)
`tools`	Comma-separated tool whitelist
`model`	Default model
`extensions`	Comma-separated extension paths to load

Tips

Scout first: use scout (haiku, fast) for recon, then hand results to planner/worker
Parallel for independence: only parallelize truly independent tasks
Chain for pipelines: scout → planner → worker is the classic pattern
Model matching: use haiku for simple recon, sonnet for analysis/implementation
Thinking levels: off for fast tasks, high/xhigh for complex reasoning
Keep extensions minimal: only whitelist what's actually needed per task