claim-verifier

An MCP server that verifies outside-world claims — so agents stop asserting things like "posted", "booked", or "merged" without proof.

The problem: AI agents routinely tell users something happened (a post went live, a PR merged, a page says X) based on a tool call that started the action, not on evidence it finished. claim-verifier is the trust layer: one assertion in, a boolean verdict plus the raw evidence out, checked live.

Tools

Related MCP server: Browser Proof

Install

npm install -g claim-verifier
# or run without installing:
npx -y claim-verifier
# or from source:
git clone https://github.com/baby-zack-agent/claim-verifier.git
cd claim-verifier && node src/index.js

Requires Node.js 18+.

MCP client config (Claude Desktop style)

{
  "mcpServers": {
    "claim-verifier": {
      "command": "npx",
      "args": ["-y", "claim-verifier"]
    }
  }
}

Or point command at a local checkout: "command": "node", "args": ["/path/to/claim-verifier/src/index.js"].

The server speaks MCP over stdio (newline-delimited JSON-RPC): initialize, tools/list, tools/call. Nothing else — no HTTP port, no hosting, no telemetry, no accounts. It runs inside your own agent.

Example session

Agent asserts: "the PR was merged."

→ tools/call verify_claim { "assertion_type": "github_merged", "repo": "octocat/hello-world", "number": 7, "kind": "pr" }
← { "verified": true,
    "evidence": { "state": "closed", "merged": true, "merged_at": "2026-…", "title": "…", "url": "https://github.com/octocat/hello-world/pull/7" },
    "checked_at": "2026-…" }

Now the agent can say "merged" — with the evidence attached.

Tool reference

verify_url

• url (string, required) — http(s) URL to fetch.

• expect_contains (string, optional) — phrase that must appear in page text (case-sensitive).

• timeout_ms (number, optional) — request timeout, default 15000.

• Returns { ok, status, final_url, redirects, title, snippet, matched, checked_at }. ok is true for 2xx statuses. matched is null when expect_contains is omitted.

verify_github

• repo (string, required) — "owner/name".

• number (integer, required) — PR or issue number.

• kind (string, required) — "pr" or "issue".

• Returns { state, merged, merged_at, title, url, checked_at }. Unauthenticated GitHub API (60 req/hour). merged/merged_at only apply to PRs.

verify_claim

• assertion_type (string, required) — "contains" | "status_2xx" | "github_merged".

• url + assertion — for contains / status_2xx.

• repo + number (+ kind, default "pr") — for github_merged.

• Returns { verified, evidence, checked_at } where evidence is the full verify_url / verify_github result.

Design notes

• Zero runtime dependencies. Hand-rolled MCP JSON-RPC over stdio using node: built-ins only. npm install pulls in nothing.

• Local-first. stdio transport; it runs inside your agent process. The only network calls are the verification targets themselves (the URL you ask about, api.github.com).

• No telemetry. Nothing phones home. Ever.

Tests

npm test

The suite spins up a local fixture HTTP server (redirects, 404, slow endpoint) and stubs the GitHub API, so it passes fully offline.

Liability disclaimer

This software is provided as-is. Verification results are a best-effort snapshot of a live, changing web — pages change, APIs rate-limit, and a "verified" result is evidence, not a guarantee. It is not legal, financial, or compliance advice. You are responsible for decisions you make based on its output.

License

MIT — see LICENSE.