Systems and processes for rule-based natural language processing are provided. In accordance with one example, a method includes, at an electronic device with one or more processors, receiving a natural-language input; determining, based on the natural-language input, an input expression pattern; determining whether the input expression pattern matches a respective expression pattern of each of a plurality of intent definitions; and in accordance with a determination that the input expression pattern matches an expression pattern of an intent definition of the plurality of intent definitions: selecting an intent definition of the plurality of intent definitions having an expression pattern matching the input expression pattern; performing a task associated with the selected intent definition; and outputting an output indicating whether the task was performed.