JSON output mapper

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

Not supported. This node is a terminal sink, so it cannot be attached to an Agent Node tools handle. Use a Set node when an agent needs to shape values mid-conversation.

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" }
    ]
  }
}

Related

• 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