how

# Explainer Prompt Template

Build the explainer subagent's prompt from this template. Fill in the placeholders.

---

You are writing an architectural explanation for a senior engineer. Multiple explorer agents have traced different slices of the codebase in parallel and gathered findings. Synthesize their findings into one coherent, well-structured explanation.

## Original Question

> {QUESTION}

## Explorer Findings

{EXPLORER_FINDINGS_ALL}

## Instructions

The explorers each investigated a different angle of the same subsystem. Their findings will overlap in places and may occasionally contradict. Reconcile them. Merge overlapping descriptions, resolve contradictions by checking the code yourself, and combine the separate slices into a unified picture.

Write an explanation a senior engineer unfamiliar with this area could read and walk away with a solid mental model, understanding the architecture well enough to start working in it confidently.

You have read-only access to the codebase to check anything, clarify a detail, or fill a gap. Use Read, Grep, and Glob as needed. The explorers did the work, so you shouldn't need to re-explore from scratch.

## Output Format

Use this structure, adapted to what makes sense for the question. Not every section is needed for every question.

### Overview
1-2 paragraphs. What is this thing, what does it do, why does it exist. Someone should be able to read just this and decide whether to keep reading.

### Key Concepts
The important types, services, or abstractions needed to follow the rest. Brief definitions, not exhaustive.

### How It Works
The core of the explanation, and the longest section. Walk through the flow: what triggers it, what happens step by step, where data goes, what the decision points are.

Use prose, not pseudocode. Reference specific files and functions so the reader knows where to look, but don't dump large code blocks unless a snippet is essential to a point.

When the flow involves multiple components talking to each other, or data transforming through stages, include a diagram. Use mermaid (```mermaid) for structured flows (sequence diagrams, flowcharts, component graphs) or ASCII art for simpler relationships where mermaid would be overkill. Use your judgment. A diagram should clarify, not decorate. If prose covers the flow, skip the diagram.

### Where Things Live
A brief file/directory map. Just the ones someone would need to start working here.

### Gotchas
Non-obvious things, surprising behavior, historical context, pitfalls. Skip this section if there's nothing worth calling out.

## Communication Style

- Use concrete language, not abstractions-about-abstractions
- Say "the `UserService` calls `AuthClient.refresh()`" not "the service delegates to the client"
- When something is complex, explain why it's complex. Don't just describe the complexity
- When something is simple, don't pad it out
- If there's a helpful analogy, use it. If there isn't, don't force one
- If the explorers flagged open questions or gaps, acknowledge them rather than hiding them

# Explorer Prompt Template

Build each explorer subagent's prompt from this template. Fill in the placeholders.

---

Other explorers are investigating different slices of the same subsystem in parallel. Don't try to cover everything. Focus on your assigned angle and go deep.

## Question

> {QUESTION}

## Your Exploration Angle

{EXPLORATION_ANGLE}

## Output

### Components Found
The key types, services, classes, and abstractions. For each: name, file path, and a one-sentence description of what it does.

### Flow
The execution flow step by step. For each step: what function/method runs, what file it's in, what it does, what it calls next. Include the data that flows between steps.

### Files Read
Every file you read during exploration, so the explainer can reference them.

### Boundaries
Where this subsystem connects to other parts of the codebase. The inputs and outputs.

### Non-Obvious Things
Anything surprising, historically motivated, or easy to get wrong. Things that look like they should work one way but work another.

### Open Questions
Anything you couldn't fully trace or understand. Be honest about gaps.

---
name: how
description: "Use for \"how does X work\", code walkthroughs before changing something, and placement / ownership / layering questions (\"where should this live\", \"which package owns this\", \"is this the right layer\"). Explains subsystem architecture, runtime flow, onboarding mental models. Use why for motivation."
disable-model-invocation: true
---

# How

Explore the codebase to answer "how does X work?" questions. Produce architectural explanations at the level of a senior engineer onboarding onto a subsystem, enough to build a working mental model, not so much that it reads like annotated source code.

Every spawn is a Task subagent with `subagent_type: generalPurpose` and `readonly: true`. Explorers use the `how explorer` line in the pstack settings file (`~/.cursor/rules/pstack-models.mdc` in Cursor, `~/.agents/pstack-models.md` in other harnesses) (default `grok-4.7-xhigh-fast`), and every explainer uses the `how explainer` line (default `claude-opus-5-5-xhigh`). Set `model` to that line's value, or to the default if the file or the line is missing. Leave `model` unset when the value is `auto` or `inherit-parent`. If your subagent tool rejects a slug, use the default and say so. If it rejects the default, use the closest valid slug of the same family from its error message or your harness's model list. Pick each subagent's reasoning level and fast or standard speed for the job, per the Subagents section of the **poteto-mode** skill.

## 1. Assess complexity

If the scope is ambiguous, state your interpretation and explore. The user can redirect.

- **Simple** (a single module, a small utility, a narrow question such as "how does function X work"): no explorers. Spawn one explainer that explores and explains in one pass, built from `references/explainer-prompt.md` without the explorer-findings section. Go to step 4.
- **Complex** (a subsystem spanning multiple files or services, a cross-cutting feature, a full architectural overview): go to step 2.

When in doubt, take the simple path.

**Other harnesses.** The spawns in this skill use Cursor's `Task` tool. In another harness, use its subagent tool: `Agent` in Claude Code (`subagent_type: general-purpose`), `task` in OpenCode (`subagent_type: general`), `spawn_agent` in Codex. Keep the prompt and the model. Drop parameters your tool doesn't have. If your harness has no subagent tool, as in Pi without an extension, run each role yourself, one after another.

## 2. Explore (complex only)

Decompose the question into 2 to 4 angles, each a distinct slice of the subsystem. Spawn all explorers in a single message, each with `references/explorer-prompt.md` and its angle filled in.

## 3. Synthesize (complex only)

Once all explorers have returned, spawn one explainer with `references/explainer-prompt.md` and every explorer's findings filled in.

## 4. Present

Present the explainer's output. Light edits for clarity or context from the conversation are fine. Do not substantially rewrite it.

## Output format

The explanation uses the sections defined in `references/explainer-prompt.md`, dropping any that do not apply: Overview, Key Concepts, How It Works, Where Things Live, Gotchas.