README.md

metadata

license: other
license_name: mixed
pretty_name: Citation-Checker Benchmark
language:
  - en
size_categories:
  - n<1K
task_categories:
  - text-classification
tags:
  - legal
  - citations
  - hallucination-detection
  - benchmark
configs:
  - config_name: charlotin-train
    data_files:
      - split: train
        path: data/charlotin-train/labels.csv
  - config_name: charlotin-test
    data_files:
      - split: test
        path: data/charlotin-test/labels.csv
  - config_name: ai-gen
    data_files:
      - split: test
        path: data/ai-gen/labels.csv

Citation-Checker Benchmark

A benchmark of whole legal briefs with hand-labelled citations, together with the reports that four citation checkers produced on those briefs: Westlaw, Lexis+, isthiscasereal.com and Hallucite. Every checker was given the same document and its report was aligned to the labels.

The inputs and labels are in data/; the checkers' raw output and our parsed results are in results/.

Components

Each component is a separate config. Components are scored and reported separately, never pooled.

config	split	documents	labelled citations	what it is
charlotin-train	train	40	567	Filings from cases in Damien Charlotin's AI Hallucination Cases database, mostly cases dated March-July 2025, plus a few early well-known cases and every S.D. Tex., W.D. Okla. and E.D.N.Y. case in the database at the time. Compiled in July 2025.
charlotin-test	test	9	158	A random sample of cases in the same database, taken in October 2026.
ai-gen	test	16	214	Motions to dismiss drafted by LLMs from real federal complaints.

Together that is 65 documents and 939 citations.

charlotin-train was used to improve Hallucite, so it is not a fair benchmark for comparing Hallucite with the other checkers. The split names reflect this. charlotin-test and ai-gen played no role in developing Hallucite.

The Charlotin components

Charlotin's database typically links only to a court order, not to the filing that contained the hallucinated citations. For each case we tried to find the original filing. When we could not obtain it (filings were sometimes stricken from the record), we either skipped the case or used the court order instead, so some documents here are orders rather than filings. The database stores metadata about the cases, not the documents; the text is public court record, included here as extracted.

ai-gen

Complaints filed in 2024 or 2025, with embedded text between 10,000 and 32,000 characters, were sampled evenly across S.D. Tex., W.D. Okla. and N.D. Okla. Each of eight models was given a complaint and a minimal prompt and asked for a motion to dismiss: GPT 4o, GPT 5, GPT 6-Sol, Claude 4 Sonnet, Claude 5 Sonnet, Gemini 2.5 Flash, Gemini 3 Flash and Gemini 3.8 Flash. The models were accessed through OpenRouter with default temperature, default reasoning levels and no tools (no internet access). No model was asked to fabricate citations. The briefs are model output, not real filings.

Files

data/<config>/<document>.txt        the document's text (also .docx: the same text, reflowed)
data/<config>/labels.csv            one row per citation occurrence (the dataset viewer shows this)
data/<config>/documents.csv         per-document metadata (briefs.csv for ai-gen)
results/<system>/<config>/          each system's raw output, exactly as produced
results/<system>/ledger.<config>.csv   our parsed result: one row per labelled citation

A document's id is its filename stem. Raw results and the label file's case_file column use the same stem, so everything joins back to its input.

The .docx files were uploaded to Westlaw and Lexis; they carry the same text as the .txt with lines reflowed into paragraphs and page-number lines dropped, because Lexis cannot read a citation that crosses a line break. isthiscasereal.com was given the same reflowed text (pasted, in pieces of at most 15 citations, since it accepts at most 20 per request).

Labels

For each document we extracted all full case citations (short-form citations and citations without a case name are excluded) and labelled each by hand, based on a search of Westlaw or Lexis. labels.csv has one row per citation occurrence.

column	meaning
case_file	the document's filename stem
cite_idx	0-based position of the citation in the document, in order of appearance
citation_text	the citation as written
citation	the cite alone, volume reporter page, normalized (e.g. 556 U.S. 662)
validity	strict, referential or invalid
parallel_citation	a second cite to the same case, where the brief gave one
correct_case_name, correct_citation	for referential rows, the correction
src_same_case_name, src_same_citation	for an invalid citation that resolves to a real case with a different name, that case's name and citation
src_notes	provenance notes carried over from the source

validity:

• strict: the citation is valid, allowing for reasonable variations in the case name.
• referential: a reader can recover the intended authority despite an understandable typo in one party name or one component of the reporter citation, with no other errors.
• invalid: the authority does not exist, or the reader cannot recover it from what is written. An invalid citation whose reporter cite points to a real case with an entirely different name is a collision (src_same_citation is filled in); otherwise it is nonexistent.

Citations are judged as the author wrote them: OCR or extraction noise in the text is not the author's error. Systems are scored under two standards: flagging only invalid, and flagging invalid plus referential.

Non-case authorities such as statutes and rules are not labelled.

Systems and results

system	product	input	run dates (2026)
westlaw	Westlaw Advantage, Litigation Document Analyzer ("Check your work")	the .docx	Oct 1-9 (charlotin-train), Oct 3-4 (charlotin-test), Oct 6-7 (ai-gen)
lexis	Lexis+ Brief Analysis	the .docx	same dates as Westlaw
isthiscasereal	isthiscasereal.com	the reflowed text, in pieces	Oct 8-14 (charlotin-train), Oct 8 (others)
hallucite	Hallucite	the .txt	Oct 14 (charlotin-train), Oct 4 (charlotin-test), Oct 7 (ai-gen)

These products change without notice, so the dates matter. Raw output is stored as the system produced it: Westlaw's full report as .rtf (Word download), Lexis's report page as .mhtml (Chrome "Single File"), isthiscasereal.com's report pages as .html. Hallucite has no raw folder here, only a ledger.

Ledgers

results/<system>/ledger.<config>.csv is our parse of the raw output, joined to the labels. It can be regenerated from the raw files and the labels. One row per labelled citation.

column	meaning
system, component, case_file, cite_idx, citation, citation_text	which citation
finding	citation_issue (the system explicitly warned), listed (returned, nothing raised) or absent (the output never mentions it)
flagged	1 if finding is citation_issue
found	1 if the system mentioned the citation at all
validity	the label, copied from labels.csv
vendor_case_name, vendor_citation	what the system printed for this citation
joined_on	how the system's entry was matched to the label: citation (exact), parallel_citation, case_at_citation, or pincite
vendor_section, vendor_resolution, vendor_reason, treatment_flag	system-specific fields

How findings are read:

• A citation is invalid if the system flags it as problematic, and valid otherwise. A citation the system's output never mentions is absent and is counted as wrong whatever the label: silence is not the same as checking a citation and finding nothing.
• No case-name matching is involved. If a system lists a different case under the citation and says nothing, that is its judgment (listed); vendor_case_name beside citation_text lets you see the substitution.
• Treatment flags (KeyCite, Shepard's) are not read as validity signals.
• Hallucite's invalid, uncovered and unpublished statuses are warnings; exists and incomplete are listed. uncovered means the reporter is outside Hallucite's data, so it could not confirm the citation; scoring that as a flag matches how the other systems treat citations they hold no data for.

Limitations

• Labels are hand-made and may contain errors.
• charlotin-train was used to improve Hallucite (above).
• Westlaw, Lexis and isthiscasereal.com were used through their web interfaces and Hallucite was run locally. Vendor products change, so these are results for those dates, not for the products in general.
• Some Charlotin documents are court orders rather than the original filings.
• ai-gen briefs contain fabricated citations produced by language models. They are not real filings.

License and provenance

The labels, ledgers and this README are released under CC-BY-4.0. The Charlotin documents are public court records. The ai-gen documents are text generated by language models from public complaints. The files under results/westlaw, results/lexis and results/isthiscasereal are the output of those services and remain subject to their owners' terms.

To request removal of anything here, contact bl759@cornell.edu.