Methods, systems, and apparatus, including computer programs encoded on computer-readable media, for workflow generation using multiple interfaces. In some implementations, an interface for defining a workflow having one or more operations for a computer system to perform is provided. The interface can provide options that are selectable to cause an operation from a predetermined set of operations to be added to the workflow. Data indicating user selection of an option of the interface corresponding to a first operation in the predetermined set of operations is received. Code that specifies one or more custom operations is received. The workflow is defined to include (i) the first operation based on the data indicating the user selection and (ii) a second operation specified by the code.