how

A codebase-exploration guide for explaining how a system works and where its parts belong.

In plain words
What is it for?
Use it for architecture walkthroughs, runtime-flow explanations, code placement questions, and design critiques.
Why use it?
It gives developers a clear mental model before they change unfamiliar code or move responsibilities between layers.

Skill for Claude CodeCodex

Install

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.

agentmods
npx agentmods add skills/ericlitman/open-pstack/how
Any agent
npx skills add ericlitman/open-pstack --skill how
Clone the repo
git clone --depth 1 https://github.com/ericlitman/open-pstack

Made for: Claude Code, Codex.

Per session 64 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,643 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

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.

ModelPer sessionOnce invoked
Fable 5 $0.00064 $0.01643
Opus 5 $0.00032 $0.00822
Sonnet 5 $0.00013 $0.00329
Haiku 4.5 $0.00006 $0.00164

Measured 2d ago against content hash 75ca4b05bc0e, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

how 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 2d ago.

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.

plugins/pstack/skills/how/SKILL.md · 122 lines

How it starts

The opening of the file, as written. The whole thing — 122 lines — stays where its author put it; the contents beside it link to each section on GitHub.

How

Explore the codebase to answer "how does X work?" questions. Produce clear architectural explanations at the level of a senior engineer onboarding onto a subsystem. Enough to build a working mental model, not annotated source code.

Dispatch contract. Resolve every configured role through provider-dispatch.md. Values are provider-qualified descriptors; the parent chooses native versus external execution. On Codex, resolve remaining Claude tool names via codex-tools.md.

Two modes:

  1. Explain (default). Explore the codebase and produce a clear explanation
  2. Critique. Explain first, then spawn multiple models to independently identify architectural issues

Explain Mode

Step 1. Understand the Question and Assess Complexity

Parse what the user is asking about:

  • "How does the rate limiter work?", a subsystem
  • "How do we handle billing for on-demand usage?", a feature flow
  • "How is the auth service structured?", an architectural overview
  • "Walk me through what happens when a user submits a form", a runtime trace

Identify the scope. If ambiguous, state your best-guess interpretation before exploring. Don't ask. Let the user redirect if you're off.

Assess complexity to decide the approach:

  • Simple (a single module, a small utility, a narrow question like "how does function X work"): skip explorer agents; the explainer explores and explains in a single pass. Go to Step 2b.
  • Complex (a subsystem spanning multiple files/services, a cross-cutting feature, a full architectural overview): spawn parallel explorer agents first, then hand off to the explainer. Go to Step 2a.

When in doubt, lean simple. You can always spawn explorers if the explainer hits a wall.

Step 2a. Explore (complex questions only)

Decompose the question into 2-4 parallel exploration angles, each a distinct slice of the subsystem so explorers don't duplicate work. Example split for "how does the rate limiter work?":

Read the full file on GitHub · 122 lines

Files

What ships with it

4 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.

Changes

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.

  1. 2d ago First seen · 122 lines · 64 tokens per session scan A 75ca4b05bc0e

Subscribe to this mod's changes

how is a skill published in the GitHub repository ericlitman/open-pstack (155 stars, last pushed 6d ago), licensed MIT. It adds 64 tokens to every session and 1,643 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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