Expressions in n8n are JavaScript-based template strings enclosed in double curly braces {{ ... }}. Mastering how n8n pairs items and executes expressions enables robust, self-healing automation.
1. The Item-Pairing Protocol
When a node executes, it processes an array of items. By default, referencing {{ $json.field }} automatically resolves the value for the matching index of the upstream item. When bridging nodes that transform array lengths (like Split In Batches or Aggregate), always use explicit item selectors like {{ $('Trigger').item.json.field }} or {{ $('Trigger').first().json.field }}.