The other side's brief
Run their brief through the checker. A filed brief is a public record, so nothing privileged leaves your desk, and every case citation in it comes back as found, not in the register, or not verifiable, with what the register holds at that volume and page.
The checker reads the PDF's text layer. A scanned filing needs OCR first; if a file has no text, the checker says so instead of returning an empty report.
On 133 filed briefs the default check took a median of 1.63 seconds per brief, before upload time. It uses no language model.
Each one says what the register holds: a different case at that citation (named), the same case at another volume, no case at that citation in a volume the register holds, or quoted words the opinion does not contain. Where the register holds a case, the row links to its entry, so you can open the opinion yourself.
"Cannot verify" is not a finding. It covers Westlaw and Lexis ids, volumes newer than the register and courts it does not fully hold. Pull those on Westlaw or Lexis, or ask opposing counsel for copies.
Turn on the deep check. For each citation it shows the passage it found, or says it could not confirm one. At the confidence it shows, it marks a wrong passage as support for 4.5% of wrong pairs (measured), so read the passage before you rely on it.
It lists every citation, what the register holds for each and the coverage statement, with the date. It is the table lawyers otherwise build by hand. See one.
"Not in the register" is a statement about our register. The report prints what the register covers, so you can tell a gap from a finding, but a gap is still possible. Rule out the ordinary reasons first: a Westlaw or Lexis id, a new volume, an unpublished decision, another citation for the same case, a name written differently. The guide to checking a citation walks through each one.
Then read the opinion at the citation yourself. Whether and how to raise it with the court is your call. The report says what the register holds, not what anyone intended.
To see how courts have dealt with citations they could not find, read the replays: ten sanctioned filings, each citation the court listed, and what the register holds at that volume and page.
Their brief is on the public docket, so uploading it discloses nothing privileged. Nothing you submit is stored unless you save it to your account: the text is processed in memory and discarded when the report comes back, and only counts are logged. That matters more for your own drafts. How that works.
Westlaw has this too. Quick Check can "Analyze your opponent's brief to view KeyCite information for their citations", and Litigation Document Analyzer on Westlaw Advantage has an "analyze an opponent's work" mode that also looks for misstatements of law (Thomson Reuters' pages, read 2026-09-24). Both need a Westlaw subscription (the analyzer needs the Advantage plan), and both add the citator, which we do not have. Neither publishes an error rate. The comparison and its sources.
The free tier gives 20 checks and 3 deep checks a month, with no account. Pay as you go is $0.50 a check, plus $0.05 for each citation the deep check reads; a 40-citation brief with the deep check comes to $2.50. Pricing.
Check their briefHow often it is wrong
A brief filed with the court is a public record, so there is no privilege question for their filing. proofread.law also keeps nothing unless you save the brief to your account: the text is processed in memory and discarded when the report is returned.
No. It means the register holds nothing at that citation and no case of that name, in a volume it does hold. That is a reason to pull the citation yourself, not a conclusion about the other side.
No open register can resolve a Westlaw or Lexis id, so they are listed together as "cannot verify" and never flagged. In filed briefs they are about a quarter of all citations. Look them up on Westlaw or Lexis.