n8n-expression-syntax

name	n8n-expression-syntax
description	Write correct n8n expressions in workflow fields. Use when writing expressions, accessing data from previous nodes, using $json, $input, $node references, JavaScript in expressions, date/time formatting, or debugging expression errors. Use when this capability is needed.
metadata	{"author":"fazer-ai"}

n8n Expression Syntax

Expert guide for writing correct n8n expressions in workflows.

Based on n8n-skills by Romuald Członkowski

Expression Basics

n8n expressions use {{ }} syntax and are evaluated at runtime:

// Access current item data
{{ $json.fieldName }}

// Access nested data
{{ $json.user.email }}

// Access array element
{{ $json.items[0].name }}

Data References

Current Node Data

// Most common - current item's JSON data
{{ $json.propertyName }}

// Binary data reference
{{ $binary.data.fileName }}

// Current item index (in loops)
{{ $itemIndex }}

Previous Node Data

// From specific node by name
{{ $node["Node Name"].json.field }}

// From input (previous node)
{{ $input.item.json.field }}

// First item from a node
{{ $node["HTTP Request"].first().json.data }}

// All items from a node
{{ $node["Webhook"].all() }}

Execution Context

// Workflow info
{{ $workflow.id }}
{{ $workflow.name }}

// Execution info
{{ $execution.id }}
{{ $execution.resumeUrl }}

// Current date/time
{{ $now }}
{{ $today }}

Common Patterns

Webhook Data Access

CRITICAL: Webhook data is nested under .body:

// ❌ Wrong - this won't work
{{ $json.message }}

// ✅ Correct - access webhook body
{{ $json.body.message }}

// Headers and query params
{{ $json.headers["content-type"] }}
{{ $json.query.paramName }}

Conditional Expressions

// Ternary operator
{{ $json.status === "active" ? "Yes" : "No" }}

// Nullish coalescing
{{ $json.name ?? "Unknown" }}

// Optional chaining
{{ $json.user?.profile?.avatar }}

String Operations

// Template literal
{{ `Hello ${$json.name}!` }}

// String methods
{{ $json.email.toLowerCase() }}
{{ $json.text.split(",")[0] }}
{{ $json.name.trim() }}

Date/Time Formatting

// Current date formatted
{{ $now.format("YYYY-MM-DD") }}

// Parse and format
{{ DateTime.fromISO($json.date).toFormat("dd/MM/yyyy") }}

// Add/subtract time
{{ $now.plus({ days: 7 }).toISO() }}
{{ $now.minus({ hours: 2 }).toFormat("HH:mm") }}

Number Operations

// Math operations
{{ $json.price * 1.1 }}
{{ Math.round($json.value * 100) / 100 }}

// Parse numbers
{{ parseInt($json.count) }}
{{ parseFloat($json.amount) }}

Array Operations

// Array length
{{ $json.items.length }}

// Map/filter
{{ $json.users.map(u => u.name).join(", ") }}
{{ $json.items.filter(i => i.active) }}

// Find
{{ $json.products.find(p => p.id === "abc") }}

Common Mistakes

1. Missing .body for Webhooks

// ❌ Wrong
{{ $json.data }}

// ✅ Correct (webhook puts data in body)
{{ $json.body.data }}

2. Wrong Node Reference Syntax

// ❌ Wrong - missing quotes
{{ $node[HTTP Request].json.data }}

// ✅ Correct
{{ $node["HTTP Request"].json.data }}

3. Accessing Non-Existent Properties

// ❌ Might error if user doesn't exist
{{ $json.user.name }}

// ✅ Safe with optional chaining
{{ $json.user?.name ?? "N/A" }}

4. Expression vs Code Node

// Expression fields ({{ }}) - single expressions only
{{ $json.name }}

// Code node - full JavaScript
const items = $input.all();
return items.map(item => ({
  json: { name: item.json.name.toUpperCase() }
}));

Special Variables

Variable	Description
$json	Current item's JSON data
$binary	Current item's binary data
$input	Input from previous node
$node["Name"]	Access specific node's output
$workflow	Workflow metadata
$execution	Execution metadata
$now	Current DateTime (Luxon)
$today	Today at midnight (Luxon)
$itemIndex	Current item's index
$runIndex	Current run index (loops)
$env	Environment variables
$vars	n8n variables

Luxon DateTime Reference

n8n uses Luxon for dates:

// Formatting
{{ $now.toFormat("yyyy-MM-dd HH:mm:ss") }}
{{ $now.toISO() }}
{{ $now.toLocaleString() }}

// Parsing
{{ DateTime.fromISO("2024-01-15") }}
{{ DateTime.fromFormat("15/01/2024", "dd/MM/yyyy") }}

// Manipulation
{{ $now.plus({ days: 30 }) }}
{{ $now.startOf("month") }}
{{ $now.endOf("week") }}

// Comparison
{{ $now > DateTime.fromISO($json.dueDate) }}
{{ $now.diff(DateTime.fromISO($json.created), "days").days }}

Expression Debugging

1. Use Set node to test expressions before complex nodes
2. Check data structure with {{ JSON.stringify($json) }}
3. Use optional chaining ?. to prevent null errors
4. Console isn't available - use Set node to inspect values

---

_{Based on n8n-skills by Romuald Członkowski • Adapted for Moltbot by fazer.ai}

---

Source: fazer-ai/moltbot-skill-n8n — distributed by TomeVault.