1. A non-transitory computer-readable medium comprising a plurality of computer instructions executable by at least one computing device, wherein, when executed, the plurality of computer instructions cause the at least one computing device to at least: in response to receiving a request for a network resource from a client, aggregate data from at least one data source for use by resource generation code supplied by a first party, the network resource being associated with a network site hosted by a second party on behalf of the first party; execute the resource generation code supplied by the first party in response to the request, the resource generation code supplied by the first party being configured to generate at least a portion of the network resource, wherein executing the resource generation code supplied by the first party comprises providing the data that has been aggregated to the resource generation code as a plurality of predefined variables, the execution of the resource generation code supplied by the first party being under control of the second party; and execute error resource generation code supplied by the first party to generate an error network resource in response to determining that an error has occurred, the error network resource being customized for the network site by the first party.