When can defendant's ANSWER determine jurisdiction?

The general rule is that jurisdiction is conferred by law and determined by the allegations made by the plaintiff in his initiatory pleading. The Supreme Court has held that jurisdiction cannot be determined by the allegations of the defendant in his answer. Hence, if, for example, a plaintiff goes to court outside Metro Manila, files his claim before a metropolitan trial court and demands to collection a sum of 50,000 pesos, the defendant cannot insist on transferring the case to a regional trial court by saying that his debt is actually more than 300,000 pesos. An otherwise rule would create a situation where the defendant can easily evade litigation by filing an answer removing the case from the jurisdiction of whatever court.

However, an exception to this rule obtains in agrarian disputes. A landlord may attempt to circumvent the law by simply filing a ejectment case against his tenant through an accion interdictal. Unsurprisingly, the defendant-tenant is forced to allege in his complaint the true nature of his relationship with the plaintiff-landlord. In such a case, the trial court should see to it that the case is resolved under the exclusive jurisdiction of the Department of Agrarian Reform Adjudication Board (DARAB).
The Supreme Court has held, "The jurisdiction of a tribunal, including a quasi-judicial agency, over the subject matter of a complaint or petition is determined by the allegations therein. However, in determining jurisdiction, it is not only the nature of the issues or questions that is the subject of the controversy that should be determined, but also the status or relationship of the parties. Thus, if the issues between the parties are intertwined with the resolution of an issue within the exclusive jurisdiction of the DARAB, such dispute must be addressed and resolved by the DARAB." (G.R. No. 127965; January 20, 2009; FRANCISCO SALAZAR, Petitioner, vs. REYNALDO DE LEON represented by his Attorney-in-Fact, FELICIANO JABONILLA, Respondent.)