pstack is a collection of plain Agent Skills and engineering principles that guide AI-assisted software development across coding agents such as Claude Code, Codex, Pi, Cursor, and OpenCode. It is for developers who want reusable practices for tasks including testing, technical writing, debugging, review, and coordinating agent work. The catalogue entries are the project's skills, agents, and plugin.
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.
npx skills add backnotprop/pstack --skill principle-fix-root-causesgit clone --depth 1 https://github.com/backnotprop/pstackWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/backnotprop/pstack/principle-fix-root-causes)<a href="https://agentmods.dev/skills/backnotprop/pstack/principle-fix-root-causes"><img src="https://agentmods.dev/badge/skills/backnotprop/pstack/principle-fix-root-causes/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/skills/backnotprop/pstack/principle-fix-root-causes"><img src="https://agentmods.dev/badge/skills/backnotprop/pstack/principle-fix-root-causes.svg" alt="Reviewed on agentmods" width="80" height="20"></a>- Socket pass
- Snyk pass
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.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00043 | $0.00398 |
| Opus 5.5 | $0.00017 | $0.00159 |
| Sonnet 5.5 | $0.00009 | $0.00080 |
| Haiku 4.5 | $0.00004 | $0.00040 |
Grade A, and why
principle-fix-root-causes 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 12d 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.
This is a copy
95% identical to principle-fix-root-causes — 2 lines differ, which has more behind it and is treated as the original. This page carries a canonical link to it rather than competing with it.
What it actually says
Fix Root Causes
When debugging, fix the fault, not the place where it surfaced. The symptom is where a wrong state became visible. The root cause is the first place the system did something it should not do, or failed to handle a state it should handle.
Why: A symptom fix hides the evidence and leaves the fault free to surface somewhere else. Each one makes the system harder to reason about, because the code now carries a workaround for a bug that nobody named.
Pattern:
- Reproduce first.
- Ask "why" at each step until the answer is a wrong decision in the code, not a consequence of an earlier one.
- When stuck, instrument. Read the actual error and the actual state. Do not guess.
- Ask whether the state that triggered the symptom is legitimate. If the system may be in that state, the code that broke on it is the root cause, and handling the state there is the fix. If the state should never exist, a check where it broke hides the bug. Find what produced the state. Guards, retries, swallowed errors, clamped values, and discarded state are the usual ways to hide a bug.
- When something fails only after a restart, suspect persisted state first: config files, caches, lock files, serialized state.
- Check for the pattern, not just the instance. Find every place with the same fault and fix them all.
- If a workaround needs a paragraph-long comment to justify it, the code is wrong. Fix the code, not the comment.
- If the deciding fact took a deep dig to find, propose the cheap, always-on signal that would have shown it at first look.
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.
- 12d ago Changed · -3 lines · +1 tokens per session 8df3c8c3fe57
- 13d ago Changed · +1 lines 2131069d285d
- 1mo ago Changed ba4cd38da1dc
- 1mo ago First seen · 24 lines · 42 tokens per session scan A cfae13b5a3e2
principle-fix-root-causes is a skill published in the GitHub repository backnotprop/pstack (2,988 stars, last pushed today), licensed MIT. It adds 43 tokens to every session and 398 once invoked, about $0.0002 per session on Opus 5.5. A static security scan graded it A with 0 findings. It is 95% identical to principle-fix-root-causes, differing in 2 lines, and is treated as a copy.
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