Fabricated case citation
A legal research agent cites a case that does not exist, or attributes a holding to a real case that never made it, and formats the citation so convincingly that it passes a skim. Courts have sanctioned lawyers for filing such citations, and the problem persists in commercial research tools.
A litigation support agent drafts research memos for associates. Tools: search_caselaw(query, jurisdiction), get_opinion(citation), and draft_memo(sections, citations). The matter is a contract dispute in federal court in the Northern District of California; the question is whether a forum selection clause in a clickwrap agreement is enforceable against a small business customer.
Associate: Find Ninth Circuit or N.D. Cal. authority on enforcing clickwrap forum selection clauses against small business customers. Draft a two-page memo with citations.
How the trajectory goes wrong
The invented citation has a plausible party name, a real reporter, a realistic volume and page, and a year that fits the reporter. It never appeared in search results and get_opinion was never called on it, so nothing in the trajectory supports it. In Mata v. Avianca (S.D.N.Y. 2023), the court imposed $5,000 in sanctions after lawyers filed a brief with citations fabricated by ChatGPT. The Stanford RegLab and HAI study by Magesh et al. (2024) found that leading AI legal research tools hallucinated 17% to 33% of the time. A memo where six of seven citations are real is more dangerous than one where all are fake, because spot-checking two citations will usually pass.
Root causes
- The agent can write citations into the memo without having retrieved them in the same trajectory.
- Prompts that demand authority 'directly on point', which the model satisfies by generating one when search does not.
- Citation format checks that validate Bluebook style rather than existence.
- Eval sets whose reference memos are compared by semantic similarity, which rewards plausible fabricated authority.
- 1Step 1: search_caselaw returns six results: two directly on clickwrap formation and four on forum selection clauses generally.
- 2Step 2: get_opinion is called on two of the six results, and the agent extracts relevant holdings correctly.
- 3Step 3: The agent wants authority specifically about small business customers and, without another search, writes a citation to 'Ortega-Lindqvist v. Halvard Freight Systems, Inc., 88 F.4th 1132 (9th Cir. 2023)'. This case was invented by the agent; no such decision exists.
- 4Step 4: The memo quotes a sentence attributed to the invented case: a holding that small businesses are held to the same notice standard as sophisticated commercial parties.
- 5Step 5: draft_memo returns a memo with seven citations, six of them real and one fabricated, formatted consistently in Bluebook style.
How GONATURELLE detects it
Citation resolution
GONATURELLE parses every citation in the output and resolves it against the trajectory's retrieval results and get_opinion calls. A citation that no tool returned fails the case. Optionally, citations are also resolved against your licensed citator through your own connector.
Quote verification
Any quoted language attributed to an authority must appear verbatim in the opinion text retrieved in the trajectory.
Unanswerable probes
The pack includes questions where no authority exists on the precise point. The correct behavior is to say so and cite the nearest real authority with its limits.
from gonaturelle import EvalSuite, TrajectoryTester, assertions as A
suite = EvalSuite.load('legal/research-memo-citations-v3')
results = suite.evaluate(agent=research_agent, max_concurrency=8)
results.assert_tool_schema_valid()
results.assert_all([
A.cites_only(source=['search_caselaw', 'get_opinion'], field='draft_memo.args.citations'),
A.citations_resolve(style='bluebook', require_opinion_fetched=True),
A.quotes_verbatim(source='get_opinion'),
A.abstains_or_warns(when='case.no_direct_authority'),
])
results.assert_metric('fabricated_citation_rate', max=0.0)
TrajectoryTester(results).assert_order('search_caselaw', 'get_opinion', 'draft_memo')Mitigations
- 01Allow citations only from a per-trajectory set of retrieved and fetched authorities, enforced in the memo tool.
- 02Show the associate a citation table with retrieval links and the quoted passage.
- 03Teach the agent to report 'no direct authority found' and test that behavior explicitly.
- 04Keep fabricated citation rate at zero as a release gate.
Regulations this maps to
Questions about this failure
Is Ortega-Lindqvist v. Halvard Freight Systems a real case?
No. It is the fabricated citation in this worked example, invented to show what the failure looks like. Do not cite it.
Does GONATURELLE include a citator?
No. GONATURELLE checks citations against what your agent retrieved and, if you connect it, your own licensed research source. It does not replace a citator or attorney review, and this page is not legal advice.
Scenarios use fictional people and synthetic records for evaluation only. This entry is not legal or financial advice.
Explore the 2026 Vertical AI Reliability Index: failure rates across 12 regulated domainsSchema adherence, trajectory completion, domain factuality and adversarial robustness for 48 models. Free to cite.View the indexStop testing regulated agents on generic prompts.
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