A citator is a tool that lists every later case that cited a judgment, and shows what each later court did with it: followed it, distinguished it, doubted it or overruled it. Lawyers use it to check that a judgment is still good law, which means that no higher court has overruled it. A citator is part of a legal research database.
Why does this matter? In India, a court must follow the earlier judgments of higher courts. Under Article 141 of the Constitution, a Supreme Court judgment binds every court in India. A High Court judgment binds the lower courts in that state. And a larger bench of judges can overrule a smaller bench of the same court. So a judgment that was good law in 2010 may have been overruled in 2020. A lawyer who relies on an overruled judgment loses the argument.
The citator uses four main words. Followed means that a later court applied the same rule. Distinguished means that a later court said the facts of its own case were different, so the rule did not apply. Doubted means that a later court questioned the rule but did not overrule it. Overruled means that a higher court, or a larger bench, decided that the rule was wrong.
Consider a lawyer in Jaipur preparing a property case. She wants to rely on a 2008 High Court judgment about the rights of tenants. She opens it in the database, and the citator lists 52 later cases that cited it. Of these, 41 followed it, 8 distinguished it on their facts and 2 doubted it. The last one, a 2019 judgment by a larger bench of the same High Court, overruled it on one point. So the citator marks the 2008 judgment with a red flag. The point she needed is exactly the one that was overruled, so she cites the 2019 judgment instead.
How does the citator know all this? First, software finds every citation inside every new judgment. A citation is the reference to an earlier case, such as its name, its year and its page in a law report. Then the publisher's legal editors read the paragraph around each citation and record how the court treated that case. Software can find the citations reliably. The treatment needs a trained person, because judges rarely write the words "we overrule".
The citator also catches cases that do not exist. AI models sometimes invent judgments, a problem called AI hallucination. If a legal AI assistant cites a case that the citator has no record of, the lawyer knows to check it before using it.
Science has the same idea. A citation database shows which later papers cited a research paper. But a citation in science rarely says whether the later paper agreed. A legal citator records exactly that.