n8n Expressions and JSON Explained for Beginners

Most n8n questions are data questions: “Why is this field empty?” “How do I use the value from an earlier node?” Understanding items and expressions answers most of them.

Items and JSON

n8n passes data as a list of items. Each item is a JSON object, a set of named fields, for example a name, an email and a city. A node usually runs once per item.

What is an expression?

An expression is a small piece of code inside double curly braces that reads data. It lets a field be dynamic instead of fixed. For example, you can set an email subject to include the name from the incoming item.

Reading data

Use the current item’s fields from the previous node.
Refer to an earlier node by its name when you need data from further back.
Use built-in helpers for dates and text, such as the current time.

The easiest way to write one is to drag a field from the input panel into a parameter; n8n writes the expression for you.

Reshaping data

The Edit Fields node lets you rename, keep or add fields. Use it to produce clean data before sending it elsewhere.

Common mistakes

Misspelling a field name (they are case sensitive).
Expecting one item when there are many.
Forgetting that an empty value from an earlier step breaks a later one.

Practise

Build a small workflow that reads rows from a sheet and creates a sentence for each, as in the Google Sheets guide. For harder shaping, see the Code node.

Quick answers

What is an n8n expression?

A small piece of code in double curly braces that reads or builds a value from your data.

Why is my field empty?

Often the field name is misspelled, the earlier node returned nothing or the data is in a different item.

Do I need to know JavaScript?

Not much. Dragging fields from the input panel writes most expressions for you.