A system and method for implementing a conditional payload server are provided. A request for a payload corresponding to a subset of client attributes is obtained. Additionally, one or more payloads are obtained in which each payload defines criteria for delivering the payload. The criteria for delivering each payload is then embodied into an expression tree, which is scored and optimized for traversal. The expression tree is converted into an evaluation tree data structure in which the conjunctive and disjunctive operators are the tree nodes and attribute evaluator value expressions are the leaf nodes. The expression tree is merged into a catalog data structure having a master attribute list, an evaluator list, a value list, a payload list, and a conjunction list. The catalog is then evaluated according to the subset of client attributes corresponding to the payload request and a payload is delivered.