1. A computer-implemented method comprising: providing, for output by a computing device on a display or with a speaker of the computing device, a prompt for a user to speak a candidate hotword that is to be designated a custom hotword, wherein a hotword is a word or phrase that indicates to a voice command processing subsystem on the computing device that one or more terms that are uttered immediately after the hotword are to be processed as voice commands; receiving, using a microphone of the computing device, one or more utterances of the candidate hotword in response to the prompt; accepting the candidate hotword as a custom hotword for the computing device based on a determination that the candidate hotword satisfies one or more hotword suitability criteria, generating, by a user interface generator of the computing device, a user interface having an indication that the candidate hotword has been accepted as a custom hotword; providing, by the computing device and in response to the one or more utterances of the candidate hotword, the indication, on the display of the computing device or using the speaker of the computing device, that the candidate hotword has been accepted as a custom hotword; after providing the indication, detecting, using the microphone of the computing device, an utterance of the custom hotword; and based on detecting the utterance of the custom hotword, causing the computing device to enter a ready state for receiving and processing voice commands uttered after the utterance of the custom hotword.