What Is a Citator?
A citator is a tool that takes a case (or statute) and reports everything that has happened to it since: every later opinion that cited it, what those opinions said about it, and — crucially — whether any of them reversed, overruled, limited, or criticized it. The output answers the question that decides whether you can rely on an authority: is it still good law?
The name “Shepardizing” comes from Shepard’s Citations, the print volumes Frank Shepard began publishing in the 1870s, which tracked citations with codes long before computers. Today Shepard’s lives on LexisNexis, its rival KeyCite on Westlaw, and both do the same job: pair editorial analysis with a complete list of citing references. Citators are the validation step — step five — of the legal research process.
Shepardizing, Step by Step
- Pull up your case on Lexis and open its Shepard’s report (or enter the citation directly into Shepard’s).
- Check the top-line signal first. Shepard’s summarizes treatment with symbols — a red signal warns of strong negative treatment such as reversal or overruling; yellow indicates possible negative treatment; other markers show positive or neutral citing history.
- Read the subsequent appellate history. Was this exact case affirmed, reversed, or modified on appeal? A trial or intermediate decision that was reversed is not authority at all.
- Work through the citing decisions, filtered by treatment (overruled by, criticized by, distinguished by, followed by) and by jurisdiction — negative treatment from your own jurisdiction’s courts matters most.
- Read the negative cases yourself. The signal tells you something happened; only the citing opinion tells you whether it kills your point. “Overruled” sometimes means overruled on an entirely different issue than the one you cite the case for.
KeyCite on Westlaw
KeyCite is Westlaw’s citator, and it works the same way with different iconography. Flags appear directly on the case: a red flag means the case is no longer good law for at least one point it decided; a yellow flag means some negative treatment short of that; Westlaw has also added an overruling-risk indicator for cases that rely on since-overruled precedent even when nothing cites your case negatively. Behind the flag sit the same layers as Shepard’s: direct appellate history, negative citing references, and the full list of citing cases, filterable by depth of discussion and jurisdiction. Which citator is “better” is a long-running debate that mostly resolves to which platform you have; serious researchers on either platform reach the same answers. See our comparison of Westlaw vs LexisNexis for the larger platform question.
Reading the Signals: Red Flags and Yellow Triangles
The signals are triage, not verdicts. Three habits keep them useful. First, a red signal is not automatically fatal: cases are often overruled on one holding while remaining perfectly good authority for another — you must identify which point drew the negative treatment. Second, a clean signal is not a guarantee: editorial analysis lags new decisions, and a statute may have been amended out from under a case without any court saying so. Third, jurisdiction weighting: criticism from another state is commentary; criticism from your controlling appellate court is a problem. The signal starts the inquiry. Reading the citing opinions finishes it.
Free Citator Options
There is no free equivalent of Shepard’s or KeyCite’s editorial layer, but free tools cover part of the job. CourtListener lists the later opinions citing any case in its database, and Google Scholar’s “How cited” tab shows citing excerpts — scan those for phrases like “overruled by” or “abrogated by” and you will catch the loudest problems. What the free route cannot do is grade treatment or promise completeness, so the sensible split is: free citation-chaining while researching, and a real citator pass on the handful of authorities you will actually rely on — via a law school, county law library, or bar association subscription if you lack your own. Our free case-law research guide shows where these tools fit in the larger workflow.
Why ‘Good Law’ Checks Are Non-Negotiable
Because the failure mode is public and career-shaping. Courts have long sanctioned lawyers for resting arguments on overruled authority, and the AI era has multiplied the opportunities to embarrass yourself — fabricated or dead citations filed without verification now generate a steady stream of sanctions opinions (collected in our guide to AI legal research tools). The rule of thumb in practice is simple and worth adopting even for academic work: no authority goes into a document until it has been citator-checked, and the check gets rerun if significant time passes before filing. It is ten minutes of work that protects everything else the research produced.