What Is a Citator? How Shepard's, KeyCite, and Modern Alternatives Verify Case Law

A citator is a legal research tool that tells you whether a case is still good law by tracking every later decision, statute, and rule that has cited, followed, criticized, distinguished, or overruled it. The two best-known citators are Shepard's on LexisNexis and KeyCite on Westlaw, which is where the verb "to Shepardize" comes from. A citator answers one question that matters before you cite anything: has this authority been reversed, overruled, or superseded since it was decided? Skipping the citator check is how lawyers cite cases that are no longer valid.

Finding a case that supports your argument is the easy half of legal research. Confirming it still stands is the half that keeps you out of trouble, and the citator is the instrument that does it. If you learned research on Westlaw or Lexis you have used one without necessarily knowing the general name. Here is what a citator actually is, how it works, and what your options are if you no longer have an enterprise seat.

What does a citator do?

A citator compiles the full citing history of a case and flags whether any of that later history undermines it. Behind the scenes it indexes every subsequent opinion, and often statutes and secondary sources, that reference your case, then classifies how each one treated it. Some later cases simply cite it in passing. Others follow it, explain it, distinguish it on the facts, criticize its reasoning, limit it, or overrule it outright. The citator sorts those signals so you can see at a glance whether the case is safe to rely on.

The headline output is a treatment signal, usually a colored symbol. A red flag or stop sign means the case has been reversed, overruled, or otherwise received strong negative treatment on at least one point. A yellow signal means caution: some negative history, a distinguishing case, or a limitation you need to read. A green or neutral signal means no known negative treatment. The symbol is a starting point, not a verdict. It tells you where to look, and you still have to read the treating case to know whether the negative history touches the exact point you are citing.

What does it mean to Shepardize a case?

To Shepardize a case means to run it through a citator to check its subsequent history and current validity. The term comes from Shepard's Citations, a system that began in 1873 as printed books of citation lists and is now LexisNexis's online citator. Lawyers used it so universally that "Shepardize" became the generic verb for the whole task, the way "Google" became a verb for search, even when the tool you are using is KeyCite or something else entirely.

The mechanics are the same whatever tool you use. You pull up your case, open its citing references, and check three things: whether it was reversed or overruled by a higher court, whether a statute has superseded the rule it stated, and whether later cases in your jurisdiction have limited or distinguished it in a way that matters to your facts. We walk through the full workflow in the guide to how to Shepardize a case.

Shepard's vs KeyCite: what is the difference?

Shepard's and KeyCite do the same job on different platforms, and for most research their coverage overlaps heavily. Shepard's lives on LexisNexis and uses its own editorial signals; KeyCite lives on Westlaw and ties into the West headnote and Key Number system. Both blend editorial analysis by attorney-editors with algorithmic citation tracking, and both are widely trusted for catching negative treatment. The practical differences are the platform you already pay for and small variations in how each classifies a borderline treatment.

The honest summary is that Shepard's and KeyCite are the deepest, and for high-stakes appellate work that depth is a real reason firms keep an enterprise seat. For everyday trial-level research, the algorithmic citators catch the large majority of what you need, at a fraction of the price.

Do you still need Shepard's or KeyCite?

Not necessarily, and this is the question that changed when Casetext shut down. For years, a strong algorithmic citator was bundled into affordable tools, and lawyers who left Westlaw and Lexis relied on it. When the standalone Casetext product closed and its citator went with it, a lot of small firms suddenly needed a Casetext replacement that still verified good law. The good news is that the citator function is no longer exclusive to the two incumbents.

What you actually need is any tool that reliably tells you a case has been reversed, overruled, or superseded before you cite it. Enterprise citators do that with the most editorial depth. Algorithmic citators on Fastcase, Bloomberg, and modern AI research tools do it well enough for most practices. What you must never do is skip the check because you no longer have Shepard's. A missing citator is not a reason to cite unverified cases; it is a reason to find a tool that includes one.

How does a citator fit an AI research workflow?

The citator is the safety layer that makes AI research trustworthy. AI is very good at finding on-point cases fast, but a case it surfaces is only useful if it is still valid, and the model itself cannot certify that. Pairing plain-English search with a built-in good-law signal closes that gap: you find the case, read the holding, and see whether later courts have undercut it, all in one pass. That is why we built the citation check into Casesearch rather than leaving verification as a separate errand.

The discipline is unchanged from the print-Shepard's era. Verify every case before you cite it, read the treating opinions the signal points to, and confirm the negative history actually touches your point rather than some unrelated holding in the same case. A citator narrows where you look; your judgment decides what it means. Run that check as the last step on whether a case is still good law, every time, and you will never file a reversed case by accident.

The bottom line

A citator is the tool that turns "this case supports my argument" into "this case supports my argument and is still good law." Shepard's and KeyCite are the deepest options and still earn their price for complex appellate work, but they are no longer the only ones that do the job, and the citator function now comes built into affordable and AI-driven tools. Whatever you use, the rule does not bend: pull the citing history, read the treatment, and confirm the case still stands before your name goes on the brief.