fact-check-verify

fact-check-verify is a command for Claude Code from axiomantic/spellbook. It costs 16 tokens per session (1,564 once invoked), scanned A, original, MIT.

A fact-checking step that verifies claims in parallel and records verdicts backed by independent evidence.

In plain words
What is it for?
Use it to check claims against code, tests, documentation, benchmarks, papers, or other sources and require a second confirmation where possible.
Why use it?
It prevents unsupported conclusions and makes resumed checks efficient by reusing claims that were already verified without relevant changes.

Command for Claude Code

Written for Claude Code: a Claude Code command (commands/*.md). Also seen: mentions AGENTS.md.

Good fit Use it to check claims against code, tests, documentation, benchmarks, papers, or other sources and require a second confirmation where possible.

Compare 6 commands from other repositories ↓
Install with agentmods
npx agentmods add commands/axiomantic/spellbook/fact-check-verify
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.

Clone the repo
git clone --depth 1 https://github.com/axiomantic/spellbook

Made for: Claude Code.

Wrote 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.

agentmods badge for fact-check-verify

README.md
[![agentmods](https://agentmods.dev/badge/commands/axiomantic/spellbook/fact-check-verify/github.svg)](https://agentmods.dev/commands/axiomantic/spellbook/fact-check-verify)
Your own site
<a href="https://agentmods.dev/commands/axiomantic/spellbook/fact-check-verify"><img src="https://agentmods.dev/badge/commands/axiomantic/spellbook/fact-check-verify/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.

agentmods 80×15 button for fact-check-verify

Your own site · 80×15
<a href="https://agentmods.dev/commands/axiomantic/spellbook/fact-check-verify"><img src="https://agentmods.dev/badge/commands/axiomantic/spellbook/fact-check-verify.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 16 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 1,564 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.
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 5.1 $0.00016 $0.01564
Opus 5 $0.00008 $0.00782
Sonnet 5 $0.00003 $0.00313
Haiku 4.5 $0.00002 $0.00156

Measured 5d ago against content hash fc13ae31a7a1, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-09, from the pricing page.

Security

Grade A, and why

fact-check-verify 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 5d 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.

commands/fact-check-verify.md · 131 lines

How it starts

The opening of the file, as written. The whole thing — 131 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Shared Reference: This command uses the evidence hierarchy and depth escalation protocol defined in skills/shared-references/evidence-hierarchy.md.

Fact-Check: Parallel Verification and Verdicts (Phases 4-5)

Invariant Principles

  1. Check the run checkpoint before re-verifying - Read .fact-checking/state.json (the current run's resume state) before re-verifying a claim; skip already-completed claims on resume and use the recorded verdict when nothing has changed in scope.
  2. Evidence requires source - Every verdict must cite code traces, test results, docs, or benchmarks.
  3. Cross-agent confirmation - A claim verified by one agent is not confirmed until a second independent agent corroborates or no contradicting evidence emerges.

Phase 4: Parallel Verification

Read the run checkpoint BEFORE verifying. Write the run checkpoint AFTER each completed claim.

The checkpoint lives at .fact-checking/state.json (project-local, gitignored). It is the run's resume artifact, not a cross-run knowledge base. The read/write contract:

  • Before verifying a claim: read the checkpoint. If the claim is in the completed list and the file referenced has not changed since the recorded timestamp (compare against git status or file mtime), reuse the recorded verdict and bibliography. If the file has changed, drop the cached entry and re-verify. Cross-run knowledge is intentionally out of scope.
  • After verifying a claim: write the verdict, bibliography entry, and timestamp into the checkpoint's findings map and append the claim index to completed. The checkpoint is the source of truth for resume; without it, a resumed run will redo work that has already been verified.

Error paths:

  • Checkpoint file missing or corrupt: treat as fresh run; do not block verification.
  • Checkpoint write fails (disk full, permissions): log and continue; verification still completes for this claim, but the run is no longer resumable from this point.
  • Swarm spawn failure: escalate to orchestrator; do not issue partial verdicts.

Read the full file on GitHub · 131 lines

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. 5d ago First seen · 131 lines · 16 tokens per session scan A fc13ae31a7a1

Subscribe to this mod's changes

fact-check-verify is a command published in the GitHub repository axiomantic/spellbook (10 stars, last pushed yesterday), licensed MIT. It adds 16 tokens to every session and 1,564 once invoked, about $0.0001 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 2026-09-03.