What free tools can catch a hallucinated case citation?

CourtListener (free, public case-law search) is the most direct free option for checking whether a case exists. It requires manually searching each citation one at a time and does not check quote accuracy or proposition support on its own.

Do Westlaw and Lexis catch AI-hallucinated citations?

Their citator tools (KeyCite, Shepard's) tell you whether a real case has been overruled or questioned, but were not purpose-built to flag fabricated citations — searching for a citation that doesn't exist typically just returns no results, which you still have to notice.

What's the difference between a general citator and a dedicated AI-hallucination checker?

A general citator (KeyCite, Shepard's) assumes the citation is real and tells you its subsequent treatment. A dedicated AI-hallucination checker is built around the opposite assumption — that the citation might not be real at all — and checks existence first.

What tools catch AI-hallucinated citations?

https://citationsafe.com/faq/tools-that-catch-ai-hallucinated-citations

Tools that catch AI-hallucinated citations fall into three broad categories: free primary-source databases you search manually, general-purpose legal citators built for a different original purpose, and dedicated citation-verification tools purpose-built for this exact problem. Each catches a different slice of the three failure modes described in what is an AI-hallucinated citation.

Category 1 — free primary-source databases

CourtListener is the standard free option: a public, nonprofit-run search engine covering federal and most state appellate opinions. Its strength is cost (free) and coverage breadth; its limitation is that you search one citation at a time by hand, and it does not natively check whether a quote attributed to a case appears in it or whether the case supports the proposition it’s cited for.

Category 2 — general-purpose citators

Westlaw’s KeyCite and Lexis’s Shepard’s were built to tell you whether a real, existing case has been overruled, questioned, or superseded — a genuinely useful and distinct check, but one that assumes the citation is real to begin with. If you search a fabricated citation, you typically get a no-results page rather than an explicit “this appears fabricated” flag, so the check still depends on the researcher noticing and acting on a blank result.

Category 3 — dedicated citation-verification tools

A newer category of tools purpose-built for the AI-hallucination problem, which run an existence check (and, depending on the tool, quote-match and proposition-support checks) across every citation in a whole document automatically rather than one at a time. Coverage varies by vendor — some check case law only, others extend to statutes and regulations; some offer a verbatim quote check, others use similarity-based matching; some publish a specific, continuously updated accuracy figure, others describe process without one. See Citation Safe vs. alternatives and the named comparisons at /vs for specifics on individual products.

Choosing between categories

For a single citation you’re double-checking, a free CourtListener search costs nothing and takes a few minutes. For a full brief with 20+ citations under time pressure, an automated tool that checks the whole document at once removes the risk of skipping a citation, and — depending on the tool — extends coverage past existence into quote accuracy and proposition support, the two failure modes an existence check alone will miss. Try Citation Safe’s free tier at /verify — 3 checks a month, no card required — alongside whatever else you’re already using, and compare the results directly.

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Layer 1–2 check (existence + quote match) against primary sources. Not legal advice.

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Written by the Citation Safe Research Desk · Reviewed by Andy Gaber, Founder