How data moves between nodes (items)

Everything n8n passes between nodes is a list of items, and each item keeps its data under "json".

Read on 14 November 2026. Products change quickly: check the sources.

The documented shape

The documentation states: all data passed between nodes is an array of objects. For most data, each item is wrapped in another object with the key json. For binary data (files), the wrapper has the key binary, and each binary entry needs data (Base64 encoded binary data). The documentation marks mimeType, fileExtension and fileName as optional but best practice.

[
  {
    "json": {
      "apple": "beets",
      "carrot": {
        "dill": 1
      }
    }
  }
]

What the Code node does for you

The page says that from n8n 0.166.0, the Function node and the Code node add the json key automatically if it is missing, and wrap your items in an array if needed. This applies only to those two nodes. If you build your own nodes, you must return data with the json key yourself.

One item at a time

When you connect nodes, data passes on automatically. A node that receives several items processes each one in turn. The documentation's example is a Trello node set to Create Card, with the name taken from a field of the incoming data: with two items, it creates two cards, each named from its own item.

Dragging a field from the input into a parameter creates an expression such as {{ $json.fruit }}. For each item the node processes, $json.fruit is that item's value.

Check your own data

The checker on the home page applies exactly these documented rules. It does not run n8n: it only tells you whether your JSON has the shape the documentation describes, and can wrap it for you.

This is an independent guide. It is not connected with n8n. Products change quickly: statements were read on 14 November 2026 from the n8n documentation pages named under Sources, and limits, defaults and version numbers may have changed since. We do not give prices or compare products.