Processing input and output in Step Functions

When a Step Functions execution receives JSON input, it passes that data to the first state in the workflow as input.

With JSONata, you can retrieve state input from $states.input. Your state machine executions also provide that initial input data in the Context object. You can retrieve the original state machine input at any point in your workflow from $states.context.Execution.Input.

When states exit, their output is available to the very next state in your state machine. Your state inputs will pass through as state output by default, unless you modify the state output. For data that you might need in later steps, consider storing it in variables. For more info, see Passing data between states with variables.

Processing input and output with JSONata

With JSONata expressions, you can select and transform data. In the Arguments field, you can customize the data sent to the action. The result can be transformed into custom state output in the Output field. You can also store data in variables in the Assign field. For more info, see Transforming data with JSONata.

The following diagram shows how JSON information moves through a JSONata task state.

Processing input and output with JSONPath

For state machines that use JSONPath, the following fields control the flow of data from state to state: InputPath, Parameters, ResultSelector, ResultPath, and OutputPath. Each JSONPath field can manipulate JSON as it moves through each state in your workflow.

JSONPath fields can use paths to select portions of the JSON from the input or the result. A path is a string, beginning with $, that identifies nodes within JSON text. Step Functions paths use JsonPath syntax.

The following diagram shows how JSON information moves through a JSONPath task state. The InputPath selects the parts of the JSON input to pass to the task of the Task state (for example, an AWS Lambda function). You can adjust the data that is sent to your action in the Parameters field. Then, with ResultSelector, you can select portions of the action result to carry forward. ResultPath then selects the combination of state input and task results to pass to the output. OutputPath can filter the JSON output to further limit the information that's passed to the output.