A virtual network verification service for provider networks that leverages a declarative logic programming language to allow clients to pose queries about their virtual networks as constraint problems; the queries may be resolved using a constraint solver engine. Semantics and logic for networking primitives of virtual networks in the provider network environment may be encoded as a set of rules according to the logic programming language; networking security standards and/or client-defined rules may also be encoded in the rules. A description of a virtual network may be obtained and encoded. A constraint problem expressed by a query may then be resolved for the encoded description according to the encoded rules using the constraint solver engine; the results may be provided to the client.