quotecheck

Does the quoted passage actually appear in the source?

AI agents (and people) often cite real sources but misstate what those sources say: real references, wrong claims. quotecheck fetches the cited source and checks that the quoted text is really there, word for word, and tells you where.

$ quotecheck "Mulberry trees" "https://en.wikipedia.org/wiki/Morus_(plant)"
{
  "status": "EXACT",
  "char_start": 9271,
  "char_end": 9285,
  "similarity": 1.0,
  "snippet": "Mulberry trees",
  "source_final_url": "https://en.wikipedia.org/wiki/Morus_(plant)",
  "reason": null
}

Built by Feenmile.

Verdicts

char_start / char_end are Python string indices (end exclusive) into the plain text quotecheck extracted from the source, which you can get with quotecheck.fetch_source(source).text.

Read NEAR carefully. A NEAR result means the wording differs. A changed number ("43,548" vs "43,549") or a dropped "not" can still score above 0.90. Use the returned snippet as the quotation, or rephrase as a paraphrase.

Related MCP server: io.github.mgdsn/verify-api-mcp

Sources

• https://... or http://... URLs

• doi:10.xxxx/... (resolved through https://doi.org, following the publisher redirect)

• pmid:12345 (the PubMed abstract, via NCBI E-utilities efetch, plain text)

Install

The PyPI distribution is named quotecheck-mcp; the import package and the command are still quotecheck.

pip install quotecheck-mcp            # library + CLI, no dependencies
pip install "quotecheck-mcp[mcp]"     # also the MCP server (needs the official mcp SDK)

Python 3.10 or newer.

Quick start: CLI

quotecheck "<quote>" <source>
quotecheck "the exact words" doi:10.1371/journal.pone.0000308
quotecheck --strict "the exact words" pmid:33301246   # exit 1 unless EXACT
echo "a long passage" | quotecheck - https://example.org/article
python -m quotecheck --help

Output is always JSON on stdout. Exit status is 0 when a verdict was printed (1 with --strict unless EXACT) and 2 for usage errors such as an empty quote.

Quick start: library

import quotecheck

result = quotecheck.check("pmid:33301246", "A total of 43,548 participants underwent randomization")
print(result.status, result.char_start, result.char_end, result.similarity)
print(result.to_dict())

# Already have the text? Skip the fetch.
quotecheck.check_text(text, quote, near_threshold=0.90)

The core library uses only the Python standard library.

Quick start: MCP server

The server speaks MCP over stdio and exposes one tool, check_quote(quote, source).

{
  "mcpServers": {
    "quotecheck": {
      "command": "quotecheck-mcp"
    }
  }
}

If the script is not on your PATH, use "command": "python", "args": ["-m", "quotecheck.mcp_server"].

The tool description tells the agent to call it before presenting text as a direct quotation, and how to act on each verdict.

Safe fetching

quotecheck fetches URLs that came from model output, so it treats them as untrusted:

• only http and https; URLs with embedded credentials are refused;

• the host is resolved and every resolved address must be public: private, loopback, link-local, multicast, reserved and unspecified addresses (including IPv4-mapped IPv6 forms) are refused; the connection then goes to the checked address, so a second DNS answer cannot swap in an internal one;

• the same checks run again on every redirect, with at most 5 redirects;

• one 15 second deadline covers the whole fetch, and the body is capped at 5 MB (declared, streamed and after decompression);

• requests identify as quotecheck/0.1 (+https://feenmile.com);

• proxy environment variables are not used.

Limits (v0.1)

• EXACT means the text appears, not that the claim is true. quotecheck does not judge context, meaning, or whether the source is reliable. A quote can be verbatim and still be used to support something the source does not say.

• No PDFs. PDF responses return SOURCE_UNAVAILABLE with the reason pdf not supported in v0.1. Many DOIs resolve to a landing page whose abstract is HTML; the full text may only be in a PDF.

• No JavaScript rendering. Pages that build their text in the browser come back empty (SOURCE_UNAVAILABLE) or incomplete (NOT_FOUND).

• Paywalls, logins, cookie walls and bot blocks. quotecheck sees what an anonymous client sees. Text behind them reads as NOT_FOUND or SOURCE_UNAVAILABLE, which does not mean the quote is wrong.

• PubMed is abstract-only. pmid: checks the abstract text, not the full paper.

• Ellipses are literal. A quote that skips words with "..." will not match exactly; check each fragment separately.

• HTML extraction is simple. Text is taken from the standard-library HTML parser with script, style and template removed. Navigation, footers and hidden elements are included; text split across unusual markup may not join the way it reads on screen.

• Unicode. Characters are NFKC-normalized one at a time; the same accented letter written in composed and decomposed forms will not match exactly.

• Fuzzy search is anchored on words shared with the quote. Quotes longer than 20,000 characters are checked for exact matches only.

• Pages larger than 5 MB are refused rather than truncated.

Development

python -m unittest discover -s tests -t .
python scripts/mutation_check.py

The tests are offline. They run a local http.server fixture. Because the SSRF guard blocks loopback, tests exempt specific fixture (ip, port) pairs with quotecheck._testing.allow_loopback_endpoints, a test-only switch that is off unless a test turns it on. A second fixture server is never exempted, so the tests can prove that a redirect into loopback is refused.

scripts/mutation_check.py copies the project to a temporary directory, disables the address check, and confirms the suite fails.

License

MIT. See LICENSE.