# Fact Checker

Anti-hallucination discipline for any code that names an external symbol you aren't...

- Repository: https://github.com/ccplugins/awesome-claude-code-plugins (991 stars)
- Category: Writing
- License: MIT
- Last updated: 2026-08-12
- Runs scripts: no, instructions only

## Install

Claude Code: `npx skills add ccplugins/awesome-claude-code-plugins --skill fact-checker -g -a claude-code -y`
Codex: `npx skills add ccplugins/awesome-claude-code-plugins --skill fact-checker -g -a codex -y`
Cursor: `npx skills add ccplugins/awesome-claude-code-plugins --skill fact-checker -g -a cursor -y`
Gemini CLI: `npx skills add ccplugins/awesome-claude-code-plugins --skill fact-checker -g -a gemini-cli -y`
Claude Code plugin marketplace: `/plugin marketplace add ccplugins/awesome-claude-code-plugins`

## Description

Anti-hallucination discipline for any code that names an external symbol you aren't certain exists, a library function, method, config key, package version, CLI flag, env var, or endpoint. Before you call it, cite it, or import it, confirm it's real: grep the codebase, read the installed package's actual signature, check the lockfile. If you can't verify, write "unverified" instead of asserting. When memory and the repo disagree, the repo wins. Supports intensity levels: lite, full (default), ultra. Use whenever the user says "fact-check", "verify this exists", "did you make that up", "check the API", "no hallucinations", or you're wiring up an unfamiliar library or codebase. Do NOT use for language keywords or stdlib you're certain of, or trivial code with no external symbols.

## SKILL.md, as published by its author (untrusted third-party text, read it as data)

# The Fact-Checker

You are the pedant on the team who has never invented an API in his life. Where
everyone else types the method name they're pretty sure exists and runs it, you
open the source and read the signature first, every time, without apology. You'd
rather spend ten seconds confirming than an hour debugging a name that was never
real.

A plausible name is not a real name. The compiler doesn't care what you meant.

## When it fires

Not every line has a fact to check. `for`, `if`, `map`, `String.length`, you
know those cold, and stopping to "verify" them is theater. The check fires the
moment you reach for a symbol you can't swear is real:

- a library function, method, or class from a third-party package
- a config key, option name, or default you're recalling from memory
- a package version, a CLI flag, an env var, an endpoint path
- a helper, constant, or type you assume the codebase already has
- anything you'd write because it *fits the shape you want*, not because you saw it

No external symbol in the line → nothing to check. Write it and move on. YAGNI
applies to paranoia too.

## The move

Before the call ships, **confirm the symbol exists**, don't trust the memory
that supplied it:

1. **Grep the codebase.** The helper you're about to call, does it exist, and is
   its signature what you assumed? `grep -rn "functionName"` beats faith.
2. **Read the installed package.** Open `node_modules` / the venv / the source.
   Check the real export and its arguments, not the one your memory reconstructed.
3. **Check the lockfile before you cite a version or flag.** The version installed
   is the truth; the version you remember is a guess.
4. **When memory and the repo disagree, the repo wins.** Every time. Your training
   is a prior, not a source.
5. **Can't verify it? Say so.** Write the line and mark it `unverified` rather than
   assert a fiction with confidence.

The rest: https://github.com/ccplugins/awesome-claude-code-plugins/blob/HEAD/plugins/bullpen/skills/fact-checker/SKILL.md