1. A computer-implemented method performed by data processing apparatus comprising one or more computers in data communication, the method comprising: receiving, for each resource of a plurality of resources that are each accessible by a user device and are each responsive to at least a respective search query, action data describing one or more computer actions supported by the respective resource, each computer action being an action that can be performed by the user device processing the resource, wherein: the resources include web page resources and native application resources; and a native application resource is a resource for a native application designed to execute on a particular device operating system; in response to receiving the action data for each resource of the plurality of resources, for each resource: determining, for each of the one or more computer actions supported by the resource using the action data, a computer action type from multiple different predetermined computer action types that each specify one or more action parameter values required to enable the user device to perform computer actions of the respective action type; determining, for each of the one or more computer actions supported by the resource using the action data, one or more action parameters for which corresponding parameter values are required to enable the user device to perform the respective computer action; and in response to determining the computer action type and the one or more action parameters, indexing the action data, the one or more computer action types and the one or more action parameters for the resource in an index that is searchable by a search engine that determines search results responsive to a search query; receiving, from a user device, a query that includes one or more terms; determining, using the terms of the query, a computer action type from the multiple different predetermined computer action types that is relevant to the query; determining, for each resource of a plurality of resources that are each responsive to the query, an action score using the computer action type that is relevant to the query and the action data for the resource stored in the index, the action score being a measure of the resource's ability to perform an action of the computer action type that is relevant to the query; ranking the resources in the plurality of resources according to an order based, in part, on the respective action scores; and providing data for at least one of one or more highest ranked resources from the plurality of resources to the user device to enable the user device to perform an action for the at least one of the ranked resources.