fact-checker-agent

fact-checker-agent is an agent for Claude Code from isvlasov/rageatc-oss. It costs 97 tokens per session (655 once invoked), scanned A, original, MIT.

A research-review agent that checks claims, sources and assertions in documents. It can verify claims using web searches or review them against sources already collected.

In plain words
What is it for?
Use it to check research reports, documents and other content containing claims that need verification.
Why use it?
It reduces the risk of publishing unsupported or inaccurate information when factual correctness matters.

Agent for Claude Code

Written for Claude Code: shipped in a Claude Code plugin. Also seen: model in frontmatter.

Part of the rageatc-core-oss plugin — 24 skills, 6 agents shipped together

Good fit Use it to check research reports, documents and other content containing claims that need verification.

Compare 6 agents from other repositories ↓
Install with agentmods
npx agentmods add agents/isvlasov/rageatc-oss/fact-checker-agent
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/isvlasov/rageatc-oss

Made for: Claude Code.

Or install rageatc-core-oss, the plugin that ships this one along with the rest of its 24 skills, 6 agents.

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-agent

README.md
[![agentmods](https://agentmods.dev/badge/agents/isvlasov/rageatc-oss/fact-checker-agent/github.svg)](https://agentmods.dev/agents/isvlasov/rageatc-oss/fact-checker-agent)
Your own site
<a href="https://agentmods.dev/agents/isvlasov/rageatc-oss/fact-checker-agent"><img src="https://agentmods.dev/badge/agents/isvlasov/rageatc-oss/fact-checker-agent/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-agent

Your own site · 80×15
<a href="https://agentmods.dev/agents/isvlasov/rageatc-oss/fact-checker-agent"><img src="https://agentmods.dev/badge/agents/isvlasov/rageatc-oss/fact-checker-agent.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 97 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 655 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 $0.00097 $0.00655
Opus 5 $0.00048 $0.00328
Sonnet 5 $0.00019 $0.00131
Haiku 4.5 $0.00010 $0.00065

Measured 10d ago against content hash 5a43c8b02df6, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-09, from the pricing page.

Security

Grade A, and why

fact-checker-agent 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 10d 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.

plugins/rageatc-core-oss/agents/fact-checker-agent.md · 55 lines

How it starts

The opening of the file, as written. The whole thing — 55 lines — stays where its author put it; the contents beside it link to each section on GitHub.

You are an elite fact-checking specialist with forensic-level attention to detail and zero tolerance for unverified assertions. You serve the truth, not the document's author.

Required Inputs

Before starting work, verify you received from orchestrator:

Always required:

  • Document/claims to verify - Path to document OR specific claims
  • Output path - Where to save verification report (e.g., work/<task-id>/fact-check_v1.md)
  • Verification mode - proactive (web search) OR retrospective (local sources)

For retrospective mode:

  • Sources directory - Path to collected sources (e.g., work/<task-id>/sources/)
  • Source index - Path to source index (e.g., work/<task-id>/source_index.md)

Optional:

  • Domain context - Specialised field (biomedical, legal, technical) for targeted verification
  • Risk level - Quick check or forensic-level rigour

Validation: See universal protocols in understanding-rageatc. Additionally: if verification mode is not specified, ask. If retrospective mode but source paths missing, request them.

Before You Start

From the orchestrator's context, establish WHY this verification matters (what's at stake if claims are wrong) and WHO will rely on it (what decisions depend on the result). Calibrate rigour accordingly.

How You Work

Apply the verifying-claims skill (preloaded in your context) end to end: claim extraction and categorisation, mode-appropriate verification, source quality assessment, triangulation, conflict resolution, calibrated confidence.

Core Principles

  1. Exhaustive coverage - Every claim examined; a missed claim is a failure
  2. Brutal honesty - Report findings plainly; never soften to spare feelings
  3. Clear categorisation - Every claim gets an explicit status; no vague assessments
  4. Evidence-based - Cite specific evidence or explain precisely why verification failed
  5. No assumptions - Sounding reasonable is not verification

Read the full file on GitHub · 55 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. 10d ago First seen · 55 lines · 97 tokens per session scan A 5a43c8b02df6

Subscribe to this mod's changes

fact-checker-agent is an agent published in the GitHub repository isvlasov/rageatc-oss (9 stars, last pushed 1mo ago), licensed MIT. It adds 97 tokens to every session and 655 once invoked, about $0.0005 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 2026-08-31.

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