AI Legal Index
Index · The accuracy question

Which AI legal research tools publish their hallucination or accuracy rates?

Index data last verified

Of the 463 legal AI vendors graded by the AI Legal Index, 16 publish measured accuracy or hallucination evidence an outsider can check, earning an A on Citation Accuracy and Hallucination Disclosure: Alexi, Aptus.AI, CoCounsel Legal, Counsel Stack, Ethyca, Harvey, Ivo, Jusbrasil, LegalOn, Midpage, NetDocuments, PatSnap, Pre/Dicta, Prudencia.ai, Relativity and Vincent AI. A further 242 vendors earn a B, meaning grounding to primary sources and cite checking are documented without a published accuracy number. The remaining 205 either claim accuracy without documentation or publish nothing on the question at all.

Every vendor on this index carries a grade on Citation Accuracy and Hallucination Disclosure, built from public sources with a verification date. The grade measures the disclosure, not the marketing: an A requires measured evidence an outsider can check without contacting the vendor, a B requires documented grounding and cite checking short of a published number, a C records a claim made without documentation, and a D records that nothing was located. Legal has a documented public record of fabricated citations reaching filed briefs, so an untested claim of accuracy is not treated as evidence here.

Vendors with published accuracy evidence

An A on this axis means the accuracy or hallucination evidence is published, measured and checkable. Hover any grade for the exact band definition.

AA on Citation Accuracy and Hallucination DisclosureMeasured accuracy is published with the test set described and the failure modes named. Output grounds to primary authority the reader can open, citation status is checked, and the system states when it found no support.
A
Alexi
Legal Research
Full grade record
AA on Citation Accuracy and Hallucination DisclosureMeasured accuracy is published with the test set described and the failure modes named. Output grounds to primary authority the reader can open, citation status is checked, and the system states when it found no support.
A
Aptus.AI
Legal Research
Full grade record
AA on Citation Accuracy and Hallucination DisclosureMeasured accuracy is published with the test set described and the failure modes named. Output grounds to primary authority the reader can open, citation status is checked, and the system states when it found no support.
C
CoCounsel Legal
General Legal Assistants
Full grade record
AA on Citation Accuracy and Hallucination DisclosureMeasured accuracy is published with the test set described and the failure modes named. Output grounds to primary authority the reader can open, citation status is checked, and the system states when it found no support.
C
Counsel Stack
Legal Research
Full grade record
AA on Citation Accuracy and Hallucination DisclosureMeasured accuracy is published with the test set described and the failure modes named. Output grounds to primary authority the reader can open, citation status is checked, and the system states when it found no support.
E
Ethyca
Regulatory & Compliance Counsel
Full grade record
AA on Citation Accuracy and Hallucination DisclosureMeasured accuracy is published with the test set described and the failure modes named. Output grounds to primary authority the reader can open, citation status is checked, and the system states when it found no support.
H
Harvey
General Legal Assistants
Full grade record
AA on Citation Accuracy and Hallucination DisclosureMeasured accuracy is published with the test set described and the failure modes named. Output grounds to primary authority the reader can open, citation status is checked, and the system states when it found no support.
I
Ivo
Contract Review & Drafting
Full grade record
AA on Citation Accuracy and Hallucination DisclosureMeasured accuracy is published with the test set described and the failure modes named. Output grounds to primary authority the reader can open, citation status is checked, and the system states when it found no support.
J
Jusbrasil
Legal Research
Full grade record
AA on Citation Accuracy and Hallucination DisclosureMeasured accuracy is published with the test set described and the failure modes named. Output grounds to primary authority the reader can open, citation status is checked, and the system states when it found no support.
L
LegalOn
Contract Review & Drafting
Full grade record
AA on Citation Accuracy and Hallucination DisclosureMeasured accuracy is published with the test set described and the failure modes named. Output grounds to primary authority the reader can open, citation status is checked, and the system states when it found no support.
M
Midpage
Legal Research
Full grade record
AA on Citation Accuracy and Hallucination DisclosureMeasured accuracy is published with the test set described and the failure modes named. Output grounds to primary authority the reader can open, citation status is checked, and the system states when it found no support.
N
NetDocuments
General Legal Assistants
Full grade record
AA on Citation Accuracy and Hallucination DisclosureMeasured accuracy is published with the test set described and the failure modes named. Output grounds to primary authority the reader can open, citation status is checked, and the system states when it found no support.
P
PatSnap
IP & Patents
Full grade record
AA on Citation Accuracy and Hallucination DisclosureMeasured accuracy is published with the test set described and the failure modes named. Output grounds to primary authority the reader can open, citation status is checked, and the system states when it found no support.
P
Pre/Dicta
Legal Research
Full grade record
AA on Citation Accuracy and Hallucination DisclosureMeasured accuracy is published with the test set described and the failure modes named. Output grounds to primary authority the reader can open, citation status is checked, and the system states when it found no support.
P
Prudencia.ai
General Legal Assistants
Full grade record
AA on Citation Accuracy and Hallucination DisclosureMeasured accuracy is published with the test set described and the failure modes named. Output grounds to primary authority the reader can open, citation status is checked, and the system states when it found no support.
R
Relativity
Litigation & eDiscovery
Full grade record
AA on Citation Accuracy and Hallucination DisclosureMeasured accuracy is published with the test set described and the failure modes named. Output grounds to primary authority the reader can open, citation status is checked, and the system states when it found no support.
V
Vincent AI
Legal Research
Full grade record

Documented grounding, no published number

A B on this axis means grounding to primary sources and cite checking are documented, and the measured accuracy number that would settle the question is not published.

The state of the market
AA on Citation Accuracy and Hallucination DisclosureMeasured accuracy is published with the test set described and the failure modes named. Output grounds to primary authority the reader can open, citation status is checked, and the system states when it found no support.16
of 463 vendors
BB on Citation Accuracy and Hallucination DisclosureGrounding is real and documented, with linked primary sources and a described retrieval method, short of published accuracy figures an outsider can test.242
of 463 vendors
CC on Citation Accuracy and Hallucination DisclosureAccuracy is asserted without measurement, or grounding is claimed while output cites sources the reader cannot open and verify.179
of 463 vendors
DD on Citation Accuracy and Hallucination DisclosureNothing published on accuracy or grounding for a product that produces legal assertions, or a bare claim that the system does not hallucinate.26
of 463 vendors

Read the shape, not just the names. The A tier is small because a published accuracy rate is a benchmark a competitor can beat and a plaintiff can quote, and most vendors have decided the safer move is a qualitative claim. The consequence for a buyer is that the loudest accuracy language in this market frequently attaches to the least measurable products, which is the exact inversion an index exists to catch.

Two signals sit alongside the grade on every vendor and answer the practical version of the question. Good Law Verification records whether a cited authority is checked for subsequent history, because a citation can be real, correctly quoted, on point, and dead. Refusal and Uncertainty Behavior records what the product does when the answer is not in the corpus, because every fabricated citation that reached a filed brief passed through a moment when the correct output was that no support could be found. On the current corpus, 40 of 463 vendors surface treatment signals and 80 of 463 document an abstention or refusal path.

Do AI legal research tools cite real cases or hallucinate citations?

It depends on the product, and the honest version of the answer is checkable rather than reassuring. The AI Legal Index records this on every vendor. 40 of 463 vendors surface subsequent history treatment, from a licensed citator or a documented treatment signal of their own, so a cited authority is flagged when it is no longer good law. 80 of 463 document what the product does when it cannot ground an answer, which is the design decision every fabricated citation passed through. The index also records the Fabricated Citation Record signal, which tracks whether a public court record exists involving output from the product, with a citation required for any adverse value.

The court record on this question is public and growing, which is why this index bounds it carefully. The Fabricated Citation Record signal records what a court order actually says, distinguishes a filer’s verification failure from findings about a product’s own output, requires a docket or reporter citation for any adverse value, and treats nothing located as a statement about the record rather than a clearance.

Method and adjacent reads

An AI Legal Index grade measures what a buyer can verify from public sources on the date shown. It is not a rating of how good the product is. A vendor can build an excellent system and grade low on an axis because it publishes nothing an outsider can check. Grading standards and limits are published on the methodology page, and every vendor named here links to its full record across all fifteen axes and twelve signals. The confidentiality side of the same diligence question is answered on which legal AI vendors keep client data out of model training, the privilege question is answered on what happens to privilege when a law firm uses a third party AI tool, the professional responsibility duties around all of it are on what the bar rules require before a lawyer uses AI on client matters, and the complete vendor set is in the directory.

Contact

Correct a record, or ask how something was graded

Every grade and every signal on this index is drawn from public sources and dated. If a record is wrong, out of date, or missing an artifact the index did not locate, send the source and it will be reviewed and the record redated. Vendors are welcome to submit documentation. Nothing on this index is for sale, including a listing, a placement, or a grade.

AI Legal Index

The AI Legal Index is an independent index that tracks changes to AI vendors in legal. It holds 462 vendors across 9 categories, each graded on the same 15 capability axes and recorded against 12 legal signals, from public sources. No vendor pays for inclusion, placement, or rating.

Index Status
Last index update
October 16, 2026
The AI Legal Index is an editorial reference. It is not a regulatory body, not a law firm, and nothing published here is legal advice or a recommendation to retain or avoid a vendor. Records are verified against published sources, bar guidance and public court records. Where a record reads not addressed, the material was not located in public sources on the date shown. See the Methodology page for evaluation standards and limitations.
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