Corroborate

The honest corroboration layer for AI agents. Hand it a claim; it tells you how independently that claim is actually being reported — and shows its work.

npm downloads license

An AP story echoed by 40 outlets is one origin, not 40 citations. Other verifiers count citations; Corroborate counts independent origins — syndication-aware — then publishes its own error rates and discloses coverage gaps. That's the judgment layer raw search and citation-checkers skip.

corroborate_claim("NASA delayed the Artemis III landing")   → CONFIRMED       4 independent origins · conf 0.9
corroborate_claim("Zorblatt Corp acquired Portugal")        → UNCORROBORATED  0 origins · conf 0.05

When an agent should call this

• Before relying on a current-event / news claim — is it independently reported, or one source echoed everywhere?
• To rank or filter sources by genuine independence, with a confidence score.
• When you need a verdict you can defend — every answer ships its evidence, its confidence, and its own caveats.

Not a web search engine (use Exa/Tavily/Brave for that) and not a human fact-checking network. It's the narrow, honest primitive in between: how independently is this reported?

Why it's trustworthy — by design

🔑 Zero API keys, zero accounts	Keyless engines (Google News RSS · GDELT · Hacker News). Nothing to sign up for.
👁 Read-only	It reads public news. It cannot act, write, spend, or touch your data.
🎯 Deterministic	No LLM in the loop — same evidence in, same verdict out. p50 ~0.4s.
📖 Open source (MIT)	Read every line of the judgment.
📊 Published error rates	We measure our own false-CONFIRMED / false-UNCORROBORATED rates on a public benchmark and print them below. Most "fact-check" tools don't.
🚫 Never lies by omission	If sources are unreachable it returns an error, never a fake "UNCORROBORATED."

What it measures — and what it doesn't

Reporting corroboration, not truth. A claim every outlet syndicated from one wire story comes back SINGLE_SOURCE. A claim nobody covers comes back UNCORROBORATED even if true. The verdict states exactly what was measured, flags its weaknesses in notes, and sets coverage:"degraded" when an engine was down — so absence of evidence is never quietly sold as evidence of absence.

Quickstart

Requires Node ≥ 18. No keys, no config.

Claude Code

claude mcp add corroborate -- npx -y corroborate-mcp

Claude Desktop / Cursor / any MCP client (claude_desktop_config.json, .cursor/mcp.json, …)

{ "mcpServers": { "corroborate": { "command": "npx", "args": ["-y", "corroborate-mcp"] } } }

Try it with no MCP client

npx corroborate-mcp   # starts the stdio server (silent = healthy)
# or from a checkout:  node cli.js "The Federal Reserve held interest rates steady"

Tools

corroborate_claim — the verdict

{ claim, window_days?=7, max_sources?=8 } →

{
  "claim": "Acme Corp acquires Widget Industries for $2 billion",
  "corroboration": "CONFIRMED",
  "n_independent_sources": 3,
  "confidence": 0.9,
  "coverage": "full",
  "sources": [
    { "headline": "Acme Corp to acquire Widget Industries in $2 billion deal",
      "outlet": "Financial Times", "domain": "ft.com", "url": "https://…",
      "published_at": "2026-07-09T14:02:00Z", "age_days": 0.9,
      "wire": false, "echoed_by_n_domains": 1 }
  ],
  "notes": ["syndication detected: near-identical headlines across multiple domains collapsed into one origin"],
  "method": "reporting-corroboration: counts INDEPENDENT story origins (syndication-aware), not raw article count; does not adjudicate truth"
}

Field	Meaning
corroboration	CONFIRMED (≥2 independent origins) · SINGLE_SOURCE (1) · UNCORROBORATED (0)
n_independent_sources	Distinct story origins after syndication clustering — not article count
confidence	0–1. Rises with origins + cross-engine agreement; penalized for wide single-origin echo
coverage	full, or degraded when an engine failed this call — a weak verdict may then reflect the outage, not the claim
sources[].wire	Origin is a wire service (AP/Reuters/AFP/UPI)
sources[].echoed_by_n_domains	How many domains carried this same story
notes	Honest caveats: syndication collapse, breaking-news cascade (<24h), relevance-gate discards, engine outages

find_sources — the raw evidence

{ query, window_days?=7, max_sources?=10 } → deduped multi-engine list (outlet, domain, url, date), no verdict. The cheaper primitive when you want the coverage and your own judgment.

Measured accuracy — because you should demand it from any fact-check tool

Against a public 40-claim labeled benchmark (benchmark/ — claims, labels, category definitions, and harness are all public; run it yourself with npm run benchmark). Latest run 2026-07-12:

Metric	Result
Fabricated claims falsely CONFIRMED	0/10
Widely-reported true claims missed	0/12 (12/12 CONFIRMED)
Niche true claims detected	7/8
Stale claims correctly windowed	3/5
Distorted claims falsely CONFIRMED	4/6 — read the warning ↓
Latency	p50 0.4s · p95 ≤8s (engine-outage worst case)

⚠️ Respect the distorted-claim number. This tool checks whether independent reporting exists around a claim's topic and entities — it does not do stance detection. A distorted version of a real event ("OpenAI released GPT-6" when it's GPT-5.6; "the EPA strengthened rules" when it weakened them) can come back CONFIRMED because real coverage token-matches it. For adversarial or detail-critical input, read CONFIRMED as "this topic has independent coverage — now check the specifics against the returned sources." Stance detection is on the v1.1 roadmap. (Recurring events like championships/elections can likewise match the current cycle's coverage.)

How the judgment works

1. Search Google News RSS, GDELT, Hacker News in parallel (keywords extracted from the claim; quoted phrases preserved).
2. Relevance gate — an article counts only if its headline genuinely addresses the claim (≥2 core-token hits AND ≥35% of core tokens). Loose topical echoes are discarded; the discard count is reported.
3. Syndication clustering — near-identical headlines across domains (Jaccard ≥ 0.55) collapse into one origin; wire domains flagged.
4. Verdict — independent origins = distinct clusters; confidence rises with origins + cross-engine agreement, falls for wide single-origin echoes; every known weakness goes in notes.

Honest limitations

• No stance detection (the 4/6 above). CONFIRMED = independently covered, not verified in every detail.
• English-language, headline-level. Paywalled body text isn't fetched.
• Recency-windowed (default 7 days, max 90). Old claims read UNCORROBORATED — a window statement, not a falsity verdict.
• Independent rewrites of one wire story can occasionally slip clustering; distinct phrasings of one origin can occasionally count as two.
• All engines down → error, never a fake UNCORROBORATED.

Development

npm test              # golden-claim suite — deterministic, no network
npm run test:mcp      # MCP stdio handshake + tools/list
npm run test:live     # live invariants against real engines
npm run benchmark     # 40-claim labeled accuracy benchmark (live, ~2 min)
npm run test:release  # all of the above — required green before every release

MIT © Ezra Cohen · github · npm