fact-checker

fact-checker is a skill for Claude Code from kalyvask/winning-writing. It costs 0 tokens per session (1,443 once invoked), scanned A, original, MIT.

A verification guide that checks factual claims in a draft, including numbers, names, dates, job titles, company details, quotations, and citations.

In plain words
What is it for?
It is for checking documents before sending or publishing them, especially when they contain statistics, named people, dates, quotes, or sources.
Why use it?
It separates confirmed claims from unverified or incorrect ones, reducing the risk that a confident-looking mistake damages trust.

Skill for Claude Code

Written for Claude Code: shipped in a Claude Code plugin.

Part of the winning-writing plugin — 32 skills shipped together

Good fit It is for checking documents before sending or publishing them, especially when they contain statistics, named people, dates, quotes, or sources.

Compare 6 skills from other repositories ↓
Install with agentmods
npx agentmods add skills/kalyvask/winning-writing/fact-checker
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.

Any agent
npx skills add kalyvask/winning-writing --skill fact-checker
Clone the repo
git clone --depth 1 https://github.com/kalyvask/winning-writing

Made for: Claude Code.

Or install winning-writing, the plugin that ships this one along with the rest of its 32 skills.

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-checker

README.md
[![agentmods](https://agentmods.dev/badge/skills/kalyvask/winning-writing/fact-checker/github.svg)](https://agentmods.dev/skills/kalyvask/winning-writing/fact-checker)
Your own site
<a href="https://agentmods.dev/skills/kalyvask/winning-writing/fact-checker"><img src="https://agentmods.dev/badge/skills/kalyvask/winning-writing/fact-checker/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-checker

Your own site · 80×15
<a href="https://agentmods.dev/skills/kalyvask/winning-writing/fact-checker"><img src="https://agentmods.dev/badge/skills/kalyvask/winning-writing/fact-checker.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 0 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,443 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 $0.00000 $0.01443
Opus 5 $0.00000 $0.00722
Sonnet 5 $0.00000 $0.00289
Haiku 4.5 $0.00000 $0.00144

Measured 12d ago against content hash ae135681c953, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-11, from the pricing page.

Security

Grade A, and why

fact-checker 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.

skills/fact-checker/SKILL.md · 90 lines

How it starts

The opening of the file, as written. The whole thing — 90 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Fact checker

Source: points/ai-writing-rules.md (section 2, Accuracy), points/exec-memo-rules.md (rules 4 and 7, on numbers and citation), points/named-failure-modes.md.

Why this exists

Every other skill in this repo makes the writing better. This one keeps it true. Those are different jobs and the second one is worth more, because style problems cost you a reader and accuracy problems cost you the relationship.

One invented number, one misattributed quote, one wrong job title — and every other number in the document becomes suspect. Credibility is a budget you spend once.

The two failure modes this catches:

  • The model made it up. LLMs fabricate confidently: invented statistics, plausible-sounding quotes attributed to real people, dates that fit the narrative. Fluency is not evidence.
  • You knew it once and it changed. Headcounts, funding rounds, job titles, pricing, product names. True in March, wrong in August. Stale facts read exactly like fabricated ones to the person who knows.

What counts as a checkable claim

Extract every instance of:

Type Examples
Numbers percentages, dollar amounts, headcounts, dates, durations, rankings, sample sizes
Named people spelling, current employer, current title, pronouns if stated
Organizations company name spelling, what they actually do, funding, ownership
Quotes exact wording, who said it, where, when
Citations does the linked source exist, and does it say what you claim
Superlatives "first," "only," "largest," "fastest" — these are factual claims, not adjectives
Implied claims "since we launched" (did you?), "our fastest-growing segment" (is it?)

Superlatives and implied claims are the ones writers forget are checkable. Treat them as claims.

Procedure

  1. Extract. List every checkable claim as a separate row before verifying anything. Quote the exact span from the draft. Do not paraphrase — the wording is what ships.
  2. Classify the source of each claim. One of: user-supplied, model-generated, or inherited from an earlier draft. Model-generated claims get the harshest scrutiny — that is where fabrication lives.
  3. Verify. Use web search for anything public. For internal claims (your own metrics), you cannot verify — say so, and ask the user for the source.
  4. Report in the table below.
  5. Rewrite the failures. For every ✗ and every ?, propose the specific replacement line.

Read the full file on GitHub · 90 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. 12d ago First seen · 90 lines · 0 tokens per session scan A ae135681c953

Subscribe to this mod's changes

fact-checker is a skill published in the GitHub repository kalyvask/winning-writing (14 stars, last pushed 6d ago), licensed MIT. It costs nothing until one of its globs matches a file; then it loads 1,443 tokens. 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 2026-08-30.

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