# Skeptic

> Review a pull request or diff adversarially — by trying to break it with hostile tests rather than reading and approving. Use when the user wants a change stress-tested against edge cases, error paths, and its own claims before merge.

- **Type:** Skill
- **Install:** `agentstack add skill-tokyubevoxelverse-skeptic-skeptic`
- **Verified:** Yes — security-reviewed for prompt injection and unsafe behavior
- **Seller:** [tokyubevoxelverse](https://agentstack.voostack.com/s/tokyubevoxelverse)
- **Installs:** 0
- **Category:** [AI & ML](https://agentstack.voostack.com/c/ai-and-ml)
- **Latest version:** 0.1.0
- **License:** MIT
- **Upstream author:** [tokyubevoxelverse](https://github.com/tokyubevoxelverse)
- **Source:** https://github.com/tokyubevoxelverse/skeptic

## Install

```sh
agentstack add skill-tokyubevoxelverse-skeptic-skeptic
```

Requires the [AgentStack CLI](https://agentstack.voostack.com/docs/cli). Works with Claude Code, Cursor, and any MCP-compatible agent.

## About

# Skeptic

A normal review reads the diff and nods. You are not a normal review. Your job is to make the change *fail* — and every attack that fails to break it becomes earned confidence. Attack the code, never the author; deliver every attack as a test they can keep.

## Phase 1 — Extract the claims

From the PR title, description, and the diff itself, write down every promise the change makes — explicit ("handles empty input") and implicit (a null-check implies null can happen; a new cache implies invalidation is correct; touched concurrency implies thread-safety). Each claim is a target. Include the silent claim every diff makes: *"nothing that worked before is broken now."*

## Phase 2 — Plan the attacks

For each claim, design inputs and states the diff's author probably didn't sit with:

- **Boundaries:** empty, singular, enormous, zero, negative, NaN/overflow, unicode and emoji, exactly-at-the-limit and one-past-it.
- **Error paths:** the dependency that throws, the file that's missing, the network that dies mid-call, the disk that's full. Error handling code is the least-tested code in every diff.
- **States assumed impossible:** call things out of order, call twice, call concurrently, reenter. If the diff says "this can't happen," that's a target painted on it.
- **The old behavior:** pick the nastiest existing usages of the touched code paths and re-exercise them.

Rank attacks by (likelihood in production × damage if it lands). Skip attacks the type system already makes impossible — hostile, not theatrical.

## Phase 3 — Execute

Write the attacks as real tests in the repo's own test framework and conventions. Run them **on the PR branch**. Then the critical control: run every *failing* attack against the **base branch** too —

- Fails on PR, passes on base → **regression.** The strongest possible finding.
- Fails on both → pre-existing weakness; report it, but don't pin it on this PR.
- A test that can't pass on base for structural reasons (new feature) is validated by making it pass trivially against the claim instead.

## Phase 4 — The report

1. **Verdict up front:** how many attacks, how many landed, merge-blocking or not.
2. **Kills** — each break: the claim attacked, the failing test, the mechanism, regression-vs-pre-existing, severity.
3. **Survived** — the attacks that didn't land. This list is the point: it's what "reviewed" should mean.
4. **The gift** — all attack tests handed over as a ready-to-commit patch, including the survivors. A PR that survives the gauntlet should merge *with* the gauntlet.

## Rules

- Never fabricate a kill: every reported break has a runnable failing test behind it.
- If the diff is untestable as structured (no seams, hardwired I/O), say so — "untestable" is itself a merge-relevant finding.
- Time-box: report the ranked attacks you didn't get to rather than silently skipping them.

## Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

- **Author:** [tokyubevoxelverse](https://github.com/tokyubevoxelverse)
- **Source:** [tokyubevoxelverse/skeptic](https://github.com/tokyubevoxelverse/skeptic)
- **License:** MIT

Install and usage instructions live in the source repository linked above.

## Pricing

- **Free** — Free

## Security capabilities

Automated source analysis of v0.1.0 — what this tool can access:

- **Network access:** no
- **Filesystem access:** no
- **Shell / process execution:** no
- **Environment & secrets:** no
- **Dynamic code execution:** no

*"Yes" means the capability is present in the source — more access means more to trust, not that it is unsafe.*


## Versions

- **0.1.0** — security scan: passed — Imported from the upstream source.

## Links

- Listing page: https://agentstack.voostack.com/l/skill-tokyubevoxelverse-skeptic-skeptic
- Seller: https://agentstack.voostack.com/s/tokyubevoxelverse
- Browse the marketplace: https://agentstack.voostack.com/browse

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Listed on AgentStack — the marketplace for AI agent skills and MCP servers. Every listing is security-reviewed. Creators keep 70%.