Data structure

In n8n, all data passed between nodes is an array of objects. It has the following structure:

[
	{
		// For most data:
		// Wrap each item in another object, with the key 'json'
		"json": {
			// Example data
			"jsonKeyName": "keyValue",
			"anotherJsonKey": {
				"lowerLevelJsonKey": 1
			}
		},
		// For binary data:
		// Wrap each item in another object, with the key 'binary'
		"binary": {
			// Example data
			"binaryKeyName": {
				"data": "....", // Base64 encoded binary data (required)
				"mimeType": "image/png", // Best practice to set if possible (optional)
				"fileExtension": "png", // Best practice to set if possible (optional)
				"fileName": "example.png", // Best practice to set if possible (optional)
			}
		}
	},
]

Skipping the 'json' key and array syntax

From 0.166.0 onwards, when using the function node, n8n automatically adds the json key if it's missing. It also automatically wraps your items in an array ([]) if needed. This is only when using the Function node. When building your own nodes, you must still make sure the node returns data with the json key.

Data flow

Nodes do not only process one "item", they process multiple ones. For example, if the Trello node is set to Create-Card and it has an expression set for Name to be set depending on name property, it will create a card for each item, always choosing the name-property-value of the current one.

This data would, for example, create two cards. One named test1 the other one named test2:

[
	{
		name: "test1"
	},
	{
		name: "test2"
	}
]