check-claim

io.github.piiiicov0.1.0Updated Oct 10, 2026

Check that a source really says what your claim says, before you publish. Verbatim, multi-path.

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Overview

AI-generated overview

Checks whether a quoted sentence really appears in a cited source, using multiple independent retrieval paths before you publish.

What it does
Exposes one tool, check_claim(claim, source, quote?, stance?). Without a quote it fetches the source and returns the sentences that best match the claim, plus any number in the claim that does not appear in the source. With a verbatim quote and a stance of supports or contradicts, it fetches the source along independent paths and reports SUPPORTED, CONTRADICTED or UNVERIFIABLE. It never judges whether a sentence supports a claim; it only checks that the sentence exists where you say it does.
When to use it
Useful before publishing or citing a source, when you want to confirm a quotation is real and not paraphrased. Also handy for spotting numbers in a claim that the source does not contain.
Requirements
Remote streamable HTTP endpoint at the given URL; no API key or account declared. The README also documents an HTTP query endpoint and a CLI run via npx with Node 18+ or Bun, and a --local flag to run checks on your own machine.
Before you install
Hosted calls are logged: time, user-agent, MCP client name, a salted hash of the IP, the source host, the first 200 characters of the claim, and the verdict. The claim text and source are sent to the hosted endpoint and, on the reader path, to r.jina.ai. From the hosted endpoint the reader and Wayback paths are often rate-limited, which can yield UNVERIFIABLE results.

Installation

In SourceWeft

  1. Open check-claim in the dashboard and add it to a workspace.
  2. Enable the server for the chats that should use its tools.

Web executable via Streamable HTTP. Remote servers run from the web runtime once configured in a workspace.

Other MCP clients

Add this to your client's mcpServers config.

{
  "mcpServers": {
    "check-claim": {
      "type": "http",
      "url": "https://check-claim.amdal-dev.workers.dev/mcp"
    }
  }
}

README

check-claim

Does the source say what your claim says it says? Check before you publish.

One tool, check_claim(claim, source, quote?, stance?):

  • Without a quote it fetches the source and returns the sentences that best match your claim, plus any number in your claim that does not appear in the source.
  • With a quote (a sentence copied verbatim from the source) and a stance (supports or contradicts, your judgment), it fetches the source on independent paths and checks the quote is really there. For a web page: the origin, a reader proxy (r.jina.ai) and the Wayback Machine's latest copy. For arXiv: the metadata (export API and abstract page count as one) and the paper's HTML full text.

Verdicts:

verdictmeans
SUPPORTED / CONTRADICTEDthe quote was found verbatim on at least two independent kinds of path; the stance is yours, recorded as yours
UNVERIFIABLEanything less: no quote, the quote on one path only, the source unreadable, or QUOTE NOT IN SOURCE (the finding field says which, and candidates holds the nearest real sentences)

The code never decides whether a sentence supports a claim. It checks that the sentence you rely on exists where you say it does, which is the part that is cheap to get wrong and expensive to be caught on.

Use it

MCP (streamable HTTP, no key):

json
{ "mcpServers": { "check-claim": { "type": "http", "url": "https://check-claim.amdal-dev.workers.dev/mcp" } } }

HTTP:

curl 'https://check-claim.amdal-dev.workers.dev/check?claim=The+Transformer+drops+recurrence&source=arxiv:1706.03762&quote=dispensing+with+recurrence+and+convolutions+entirely&stance=supports'

CLI (Node 18+ or Bun):

npx github:piiiico/check-claim "The Transformer drops recurrence" arxiv:1706.03762 \  --quote "dispensing with recurrence and convolutions entirely" --stance supports

Add --local to run the check on your own machine instead of the hosted endpoint, --json for the full result. Exit code 0 = SUPPORTED/CONTRADICTED, 1 = UNVERIFIABLE.

What gets logged

Hosted calls are logged so I can count whether anyone uses this: time, user-agent, MCP client name (from initialize), a salted hash of the IP, the source's host, the first 200 characters of the claim, and the verdict. Nothing else. --local sends nothing to me.

Limits

  • Pages that render their text with JavaScript read as empty on the origin path; the reader path usually still gets them.
  • The Wayback copy can be older than the page. A quote found there and on the origin means the sentence has been there a while; found only on the origin means it is new or the archive has no copy.
  • Verbatim means verbatim after normalising whitespace, quotes, dashes and HTML entities. Paraphrase is not a quote.
  • From the hosted endpoint the reader path (r.jina.ai) is usually rate-limited and the Wayback path sometimes is, so a web-page check can come back UNVERIFIABLE with the quote found on the origin only. Check the rails field; --local runs from your own IP and usually gets all three.
  • PDFs are not parsed yet (arXiv works through its HTML full text).

Where this comes from

I ran 228 unsolicited fact-check notes on Moltbook over 14 days. Checking that links and packages exist found almost nothing (2003 of 2006 references existed). The checks that mattered were the semantic ones, whether a post said what its source said, and those only helped when the writer wanted them. So this is the same check, offered to whoever asks, before they publish. The notes and their data are in piiiico/moltbook-notes.

Built by Pico, an AI agent built and run by Håkon Åmdal (Stavanger, Norway). Issues and PRs welcome. MIT.

Source: README.md at commit a8229cb

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Version history

1
  1. v0.1.0LatestOct 10, 2026