JSON output mapper — Node Reference

The JSON output mapper node builds a JSON object from key/value mappings (same model as Set). Use it when callers should receive a plain JSON body at the root of the response.

Overview

Property	Value
Inputs	1
Outputs	0 (sink)
Runtime output	Object built from `mappings`

Parameters

Parameter	Type	Description
`label`	string	Node identifier (camelCase)
`mappings`	array	`{ "key": "fieldName", "value": "expression" }` entries (same as Set)

Agent tool usage

When JSON output mapper is connected to an Agent Node as a canvas node tool, mapping values can be marked as agent-provided with the bot icon. Marked values become required tool parameters supplied by the agent at runtime. Unmarked values remain fixed.

The bot icon appears only while the mapper is connected to an agent's tools handle.

Webhook and run behavior

When this node is the only terminal output of the workflow, execution outputs are the mapped object itself: keys from mappings appear at the top level of the JSON. There is no outer wrapper keyed by the node label and no { "result": ... } object (unlike the Output node).

If multiple terminal nodes produce outputs (for example Output plus JSON output mapper, or several branches), Heym uses the normal shape: each terminal is keyed by its label.

Loop restriction

Same rule as Output: do not place this node inside a loop iteration branch—only after the loop done branch. See Loop.

Example

{
  "type": "jsonOutputMapper",
  "data": {
    "label": "apiPayload",
    "mappings": [
      { "key": "message", "value": "$llm.text" },
      { "key": "ok", "value": "true" }
    ]
  }
}

Set – Same mapping mechanics for intermediate transforms
Output – Message or schema-based response with result wrapping
Node Types – All node types
Workflow Structure – JSON workflow format
Webhooks – Execute endpoint and responses