# Fact Check

> Verifies claims in backlog items, skill documentation, or plugin content against primary sources using web lookups. Spawns parallel verification agents that must use WebFetch/WebSearch/gh — training data recall is explicitly rejected as evidence. Produces VERIFIED/REFUTED/INCONCLUSIVE verdicts with citations. Use when items are marked UNVERIFIED or when verifying tool API claims, CLI flags, or do…

- **Type:** Skill
- **Install:** `agentstack add skill-jamie-bitflight-claude-skills-fact-check`
- **Verified:** Yes — security-reviewed for prompt injection and unsafe behavior
- **Seller:** [Jamie-BitFlight](https://agentstack.voostack.com/s/jamie-bitflight)
- **Installs:** 0
- **Category:** [Agent Skills](https://agentstack.voostack.com/c/agent-skills)
- **Latest version:** 0.1.0
- **License:** MIT
- **Upstream author:** [Jamie-BitFlight](https://github.com/Jamie-BitFlight)
- **Source:** https://github.com/Jamie-BitFlight/claude_skills/tree/main/.claude/skills/fact-check

## Install

```sh
agentstack add skill-jamie-bitflight-claude-skills-fact-check
```

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

## About

# Fact Check — Primary Source Claim Verification

Verify factual claims against primary sources using web lookups. Training data recall is NOT evidence.

---

## When to Use

- Backlog items marked `UNVERIFIED`
- Plugin documentation with uncited claims about tools, APIs, CLI flags
- Skills that reference specific software behavior without citation
- After code review agents flag potential fabrication

## When NOT to Use

- Structural findings (broken links, missing files, malformed YAML) — those are filesystem checks, not fact checks
- Code logic bugs — use `/find-cause` instead
- Research on new tools — use `/research-curator` instead

---

## Evidence Rules

Adapted from the `find-cause` evidence chain protocol.

**Valid evidence** (one of these MUST support each verdict):

1. **WebFetch output** — content retrieved from an official documentation URL
2. **WebSearch result** — search results linking to authoritative sources
3. **Command output** — `npx  --help`, `gh api`, or similar CLI output
4. **Repository source code** — file content from the tool's GitHub repo via `gh` or clone
5. **MCP tool output** — `mcp__Ref`, `mcp__exa` results with URLs

**NOT valid evidence** (these MUST NOT support verdicts):

- Training data recall ("I know this from my training")
- Inference from absence ("the docs don't mention it, so it doesn't exist")
- Reasoning from analogy ("tool X works this way, so tool Y does too")
- Documentation that describes intent without observed behavior
- Another AI's claim without primary source backing

---

## Claim Extraction

Parse the input to extract discrete, falsifiable claims:

```mermaid
flowchart TD
    Start([Parse input]) --> Q{Input type?}
    Q -->|Backlog item title| ReadBacklog[Run backlog list --format json, find matching item]
    Q -->|Plugin path| ScanFiles[Scan SKILL.md and references for factual claims]
    Q -->|--all-unverified| FindAll[Run backlog list --format json, filter UNVERIFIED items]
    ReadBacklog --> Extract[Extract falsifiable claims]
    ScanFiles --> Extract
    FindAll --> Extract
    Extract --> Classify[Classify each claim]
    Classify --> Spawn[Spawn verification agents]
```

### Claim Classification

For each claim, determine:

1. **Claim text** — the specific assertion
2. **Primary source** — where to check (official docs URL, GitHub repo, CLI help)
3. **Verification method** — WebFetch URL, run CLI command, search GitHub issues
4. **Falsifiability** — what would disprove this claim?

---

## Verification Agent Spawning

Spawn `@fact-checker` agents in parallel waves of 5.

Each agent receives:

```text
CLAIM: {exact claim text}
SOURCE_FILE: {file containing the claim, with line numbers}
PRIMARY_SOURCE: {URL or command to check against}
VERIFICATION_METHOD: {WebFetch | WebSearch | CLI command | gh API}
FALSIFICATION_CRITERIA: {what would disprove this}
```

### Wave Execution

```mermaid
flowchart TD
    Start([Claims extracted]) --> Count{How many claims?}
    Count -->|1-5| Wave1[Wave 1 — all in parallel]
    Count -->|6-10| Split2[Wave 1 — first 5, Wave 2 — remaining]
    Count -->|11+| SplitN[Waves of 5, sequential]
    Wave1 --> Collect[Collect verdicts]
    Split2 --> SeqWaves[Execute waves sequentially]
    SeqWaves --> Collect
    SplitN --> SeqWaves
    Collect --> Report[Generate report]
```

---

## Verdict Format

Each agent returns a structured verdict:

```text
CLAIM: {the claim being checked}
VERDICT: VERIFIED | REFUTED | INCONCLUSIVE
EVIDENCE:
  - Source: {URL or command}
  - Retrieved: {date}
  - Content: {relevant excerpt from primary source}
EXPLANATION: {how the evidence supports the verdict}
CITATION: {formatted citation for backlog/docs update}
```

### Verdict Criteria

- **VERIFIED** — primary source confirms the claim. Evidence excerpt matches.
- **REFUTED** — primary source contradicts the claim. Evidence excerpt shows the discrepancy.
- **INCONCLUSIVE** — primary source could not be reached, does not address the claim, or is ambiguous. State what additional step would resolve it.

---

## Chain of Verification (CoVe) Requirement

Each agent MUST apply CoVe before finalizing:

1. **Initial lookup** — fetch primary source, form initial verdict
2. **Verification questions** — generate 2-3 questions that could falsify the initial verdict
3. **Independent check** — answer each verification question using a different source or method
4. **Final verdict** — confirm or revise based on cross-checking

This prevents the agent from confirming its own bias in a single lookup.

---

## Report Format

After all waves complete:

```markdown
# Fact Check Report

**Date**: {YYYY-MM-DD}
**Scope**: {backlog item title | plugin path | all-unverified}
**Claims checked**: {N}

## Summary

| Verdict | Count |
|---------|-------|
| VERIFIED | {N} |
| REFUTED | {N} |
| INCONCLUSIVE | {N} |

## Verdicts

### Claim 1: {claim text}

**Verdict**: {VERIFIED|REFUTED|INCONCLUSIVE}
**Source**: {primary source URL}
**Evidence**: {excerpt}
**Citation**: {formatted citation}

### Claim 2: ...

## Backlog Updates

{For each REFUTED or VERIFIED claim, the specific edit to make to the per-item file}
```

---

## Post-Actions

1. **Update backlog** — for VERIFIED/REFUTED claims, update the backlog item's Status field in the per-item file
2. **Lint** — `uv run prek run --files .claude/backlog/`
3. **Commit** — `git add .claude/backlog/ && git commit -m "docs(backlog): fact-check {N} claims ({date})"`

For INCONCLUSIVE claims, add a note to the backlog item describing what additional verification is needed.

---

## References

- Evidence chain protocol adapted from [find-cause](./../../skills/find-cause/SKILL.md)
- Wave spawning pattern from [research-curator](./../../skills/research-curator/SKILL.md)
- Anti-hallucination checkpoint from [skill-research-process](./../../skills/skill-research-process/SKILL.md)
- Chain of Verification from [cove-prompt-design](./../../skills/cove-prompt-design/SKILL.md)

## Source & license

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

- **Author:** [Jamie-BitFlight](https://github.com/Jamie-BitFlight)
- **Source:** [Jamie-BitFlight/claude_skills](https://github.com/Jamie-BitFlight/claude_skills)
- **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-jamie-bitflight-claude-skills-fact-check
- Seller: https://agentstack.voostack.com/s/jamie-bitflight
- Browse the marketplace: https://agentstack.voostack.com/browse

---
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