The short answer
Check every citation in the brief against a record of real decisions, and then check it again for the things a lookup can’t see. The case has to exist. It has to be the case the brief names. Any quoted words have to be in it, and it has to say what the sentence claims. A free checker can do the first three mechanically. The fourth, and whether the case is still good law, is still yours.
Why this keeps happening
A language model writes text that looks like the text it learned from. A citation has a very regular shape (a volume, a reporter, a page, a court, a year), so a model can produce one that looks exactly right and points at nothing, or at some other case. It isn’t lying; it has no record to look anything up in.
Courts have sanctioned lawyers for filing briefs built on citations like this. The best-known case is Mata v. Avianca, Inc., No. 22-cv-1461 (S.D.N.Y. June 22, 2023), where the court found that several of the decisions a brief relied on did not exist.
Five ways a citation can be wrong
- It doesn’t exist. No case is at that volume and page.
- It’s a different case. The citation is real, but it belongs to a case with a different name. This is the most dangerous kind, because a check that only asks “is something there?” will pass it.
- The quotation isn’t in it. The case is real and right, but the quoted words aren’t the court’s, or they’ve been changed.
- It doesn’t say that. The case is real and quoted correctly, but it doesn’t support the proposition it’s cited for, or the passage is from a dissent.
- The reporter is wrong. A typo, or a reporter abbreviation that doesn’t exist. Sometimes a slip, sometimes a sign the citation was never real.
What to check, citation by citation
- Does the citation resolve to a real decision?
- Is the name the brief gives the name of the case at that citation?
- Is every quotation in the opinion, word for word, and in the majority opinion rather than a dissent?
- Does the pinpoint page fall inside the opinion?
- Does the case support the sentence it’s attached to?
- Is it still good law? That needs a citator (KeyCite or Shepard’s). No free tool, including ours, can answer it.
How our free checker does the first four
Paste a brief or drop a .docx, .pdf or .txt file into the checker.
- The brief stays on your computer. It’s read in your browser tab. The citations are found there, and you see the exact list before anything is sent.
- Only the citation numbers leave: a volume, a reporter and a page. Not the case names, not your argument, not the text around them. They’re checked against our own copy of the case law, and the ones our copy doesn’t hold are checked against CourtListener, a public database run by the non-profit Free Law Project, still as numbers only.
- You see the case at each citation, with its court and date, so a citation that belongs to a different case shows up as a different name.
- Quotations are checked against the opinion’s own words. The opinion comes to your browser and the comparison happens there, so your quotations aren’t sent. You see whether the words are there, where they differ, and whether they’re in a dissent or concurrence.
- Statutes, regulations, court rules and dockets are checked too: the US Code, the Code of Federal Regulations, the Federal Register, the federal rules, many courts’ local rules, and unreported decisions cited by docket number and date.
- It also flags reporters it doesn’t recognise, text in the document a reader can’t see, and citation-format slips, and it builds a table of authorities.
No AI model is involved in any of this. A citation is either in the record or it isn’t, and the answer is shown so you can check it.
What “found” means: the case exists. It doesn’t mean the case is still good law, and it doesn’t mean it supports what you wrote. What “not found” means: it isn’t in the sources we check, which is not proof it was invented. Recent, unpublished and state trial-court decisions are the usual gaps. The coverage page lists every court and code we hold.
More on the checker itself: the free citation checker, and for a whole matter, Zero Witness for legal work. Related guides: How to build a table of authorities without uploading your brief · How to get a deposition summary from AI that you can check · Can you put client information into an AI chatbot?. All guides.