1. A computer-implemented method comprising: receiving data specifying a new voice action, the data identifying (i) an application, (ii) a voice command trigger phrase for triggering the application, and (iii) a context that must be satisfied for the application to be triggered; generating a data structure instance that specifies (i) the application, (ii) the voice command trigger phrase, and (iii) an alternate voice command trigger phrase, the alternate voice command trigger phrase being based on the received voice command trigger phrase; and after generating the data structure instance, enabling triggering of the new voice action by a spoken utterance based at least on storing the data structure instance at a database that comprises a plurality of other data structure instances, wherein each of the other data structure instances specifies (i) an application, and (ii) one or more voice command trigger phrases; determining that the context is satisfied; after enabling the triggering of the new voice action and based at least on determining that a transcription of a spoken utterance includes the alternate voice command trigger phrase specified by the generated data structure instance, selecting the generated data structure instance from the database; and based on the selection of the generated data structure instance and based on the determination that the context is satisfied, causing an activity associated with the application specified by the generated data structure to be performed on or by the application.