How do I return the original input items for each output item in my n8n workflow?

Below is a concise explanation that should help you resolve the issue:

The Issue

When you see:

JSCopied
To make sure expressions after this node work, return the input items that produced each output item.

it means that any node using the output of the current node expects to have a reference back to the original input items. In other words, if you modify the data (for example, by using code to parse JSON), you must make sure that the output items still include the properties and structure of the original input items.

How to Fix It

There are two common approaches:

1. Include the Original Data:
   When using nodes such as the Edit Fields node, ensure that your output includes the incoming (original) data. In the Edit Fields node you have an Include in Output option. Set this option to include All Input Fields (or at least the fields that subsequent nodes expect). This makes sure that each output item holds the data that produced it.

2. Return the Input Items in Code Nodes:
   If you’re using a Function (or Code) node to manipulate data, make sure that you return an array where each item is built from the original input. For example, if you’re adding or modifying fields, a common pattern is:

   JSCopied
   // For each incoming item, merge the new data while preserving the original input values.
   return items.map(item => {
     return {
       json: {
         ...item.json,
         // Add or update fields as needed
         newField: 'new value'
       }
     };
   });

   This way, every output item contains the original JSON data (i.e. the input that produced it), ensuring that any expressions further down the workflow (that reference $input.item) can access the expected data.

Why It Works

n8n depends on linking each output item to its originating input, so that expressions in subsequent nodes (which might reference properties like {{$input.item.json...}}) can correctly evaluate. If you omit these original input items during transformations, the node will show the warning you've encountered.

Summary

• For JSON Output Mode (e.g., in Edit Fields):
  Make sure you have Include in Output set to include the original input data. This is why when using synthetic data from the Edit Fields node the issue does not occur—the node is already set up to output that information.

• For Code/Function Nodes:
  Always return the full items (or merge new data with the original item) rather than creating completely new objects that lack the internal structure n8n needs.

By ensuring that every node outputs the input items along with any modifications, you'll prevent these alerts and guarantee that expressions further in your workflow have access to the expected data.