pstack-claude is a set of opinionated coding-agent skills and workflows ported from Cursor to Claude Code, Codex, Pi, and other agent harnesses. It guides agents toward concise, simple, and verified code by routing goals to suitable workflows and supporting subagent tools. The catalogue entries are the project's skills, agents, hook, and plugin implementations for these agent environments.
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 michael-denyer/pstack-claude --skill maintain-formal-verification-skillgit clone --depth 1 https://github.com/michael-denyer/pstack-claudeWrote 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/michael-denyer/pstack-claude/maintain-formal-verification-skill)<a href="https://agentmods.dev/skills/michael-denyer/pstack-claude/maintain-formal-verification-skill"><img src="https://agentmods.dev/badge/skills/michael-denyer/pstack-claude/maintain-formal-verification-skill/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/michael-denyer/pstack-claude/maintain-formal-verification-skill"><img src="https://agentmods.dev/badge/skills/michael-denyer/pstack-claude/maintain-formal-verification-skill.svg" alt="Reviewed on agentmods" width="80" height="20"></a>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 | $0.00107 | $0.01624 |
| Opus 5.5 | $0.00043 | $0.00650 |
| Sonnet 5.5 | $0.00021 | $0.00325 |
| Haiku 4.5 | $0.00011 | $0.00162 |
Grade A, and why
maintain-formal-verification-skill 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 today.
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.
Copies of this mod
1 near-identical copy found in the catalogue:
- maintain-formal-verification-skill — 89% identical, 13 lines differ
How it starts
The opening of the file, as written. The whole thing — 62 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Maintain a formal verification skill
On Codex, read the platform mapping, including its per-skill notes, before following this skill.
On GitHub Copilot, read the platform mapping, including its per-skill notes, before following this skill.
A formal check proves a property of what it describes. When the code changes and the verification does not, the check can keep passing while it describes code that no longer exists. That pass is the dangerous case, because it looks like a proof. This skill is the upkeep loop for a formal verification skill that /create-formal-verification-skill generated, or for any project-local skill that runs a model checker, prover, or code-level verifier against named code. The project-local skill handles a change that an agent makes while it uses that skill. This skill handles the changes that skipped it: merges, edits made without the skill, and drift that builds up across many commits.
Outcomes
Give each check one outcome, and say which:
- in sync: no change since the last sync alters what the check describes, and the check passes.
- updated: the code changed, the verification now describes the new code, and the check passes.
- bug: the verification describes the current code, and the code breaks the property. This is a finding about the code. It is not drift.
- blocked: the check could not be brought back in line or could not run. Say exactly why.
A check can be both updated and bug: the update makes the verification describe the code again, and then the property fails on it.
Edit scope
Edit only the verification: models, harnesses, property files, and the formal verification skill itself. Never edit product code during a run, unless the user asks you to. When a property fails on the current code, do not weaken the property or the model to make it pass. Report the failure.
Pass
- Find the checks. A formal verification skill has no fixed name, so find it by what it does: a project skill that runs a model checker, a prover, or another verifier against named code. The project
verifyskill that/create-verification-skillwrites drives the app and is not one. Read each one you find, or the one the user named. For each check, collect the property, the code it covers, the bounds and assumptions, the command that runs it, and the commit where it was last confirmed to describe the code. If no formal verification skill exists, stop and point at/create-formal-verification-skill. If the skill does not record a sync commit, use the last commit that changed the verification files, and say that you did.
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.
- today First seen · 62 lines · 107 tokens per session scan A 2b2b29086114
maintain-formal-verification-skill is a skill published in the GitHub repository michael-denyer/pstack-claude (3,082 stars, last pushed yesterday), licensed MIT. It adds 107 tokens to every session and 1,624 once invoked, about $0.0004 per session on Opus 5.5. 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 2026-10-20.
Other skills, from other repositories
prevent-recurrence
Use when correcting an issue or failure reveals a reusable prevention lesson, including code, setup, measurement, validation, workflow, agent mistakes, or accepted code-review findings; when someone says "this keeps happening" or asks how to stop it; or in post-incident follow-up. Fixes the instance (failing-first…
fix-bug
Run the Fix Validation pipeline to investigate, fix, and validate a bug. Ensures deterministic pipeline execution with IssueAnalyzer, FixWriter, TestWriter (conditional), TestAudit (conditional), and FixValidator stages.
test-triage
Classify failing tests as flaky vs. real regressions and propose a next step for each. Invoke when the user pastes failing test output, asks to triage CI failures, or asks "are these tests flaky".
backpropagation
Trace runtime bugs back to spec gaps — identify missing acceptance criteria, update specs, generate regression tests, and detect patterns.
systematic-debugging
Apply structured debugging techniques to find and fix bugs efficiently. Use when the user reports a bug, encounters unexpected behavior, says something is "not working", or asks for help debugging. Apply hypothesis-driven debugging instead of random changes.
bugbash
Systematically explore and test any software project (CLI, API, Backend, Library, etc.) to find bugs, usability issues, and edge cases. Produces a structured report with full reproduction evidence (exact commands, inputs, logs, and tracebacks) for every issue.