N8n Expression Syntax

Overview

Expert guide for writing correct n8n expressions in workflows. All dynamic content in n8n uses double curly braces: {{expression}}.

When to Use

• You need to write or debug n8n expressions using {{ ... }} syntax.
• The task involves $json, $node, webhook payloads, or expression-related workflow errors.
• You want syntax-correct dynamic values inside n8n nodes and parameters.

Prerequisites

• Access to an n8n instance or workflow JSON file.
• (Optional) n8n MCP tools for validation.

Procedure

1. Expression Format

All dynamic content in n8n uses double curly braces:

{{expression}}

Examples:

✅ {{$json.email}}
✅ {{$json.body.name}}
✅ {{$node["HTTP Request"].json.data}}
❌ $json.email  (no braces - treated as literal text)
❌ {$json.email}  (single braces - invalid)

2. Core Variables

$json - Current Node Output

Access data from the current node:

{{$json.fieldName}}
{{$json['field with spaces']}}
{{$json.nested.property}}
{{$json.items[0].name}}

$node - Reference Other Nodes

Access data from any previous node:

{{$node["Node Name"].json.fieldName}}
{{$node["HTTP Request"].json.data}}
{{$node["Webhook"].json.body.email}}

Important:

• Node names must be in quotes
• Node names are case-sensitive
• Must match exact node name from workflow

$now - Current Timestamp

Access current date/time:

{{$now}}
{{$now.toFormat('yyyy-MM-dd')}}
{{$now.toFormat('HH:mm:ss')}}
{{$now.plus({days: 7})}}

$env - Environment Variables

Access environment variables:

{{$env.API_KEY}}
{{$env.DATABASE_URL}}

3. Common Patterns

Access Nested Fields

// Simple nesting
{{$json.user.email}}

// Array access
{{$json.data[0].name}}
{{$json.items[0].id}}

// Bracket notation for spaces
{{$json['field name']}}
{{$json['user data']['first name']}}

Combine Variables

// Concatenation (automatic)
Hello {{$json.body.name}}!

// In URLs
https://api.example.com/users/{{$json.body.user_id}}

// In object properties
{
  "name": "={{$json.body.name}}",
  "email": "={{$json.body.email}}"
}

4. Advanced Patterns

Conditional Content

// Ternary operator
{{$json.status === 'active' ? 'Active User' : 'Inactive User'}}

// Default values
{{$json.email || 'no-email@example.com'}}

Date Manipulation

// Add days
{{$now.plus({days: 7}).toFormat('yyyy-MM-dd')}}

// Subtract hours
{{$now.minus({hours: 24}).toISO()}}

// Set specific date
{{DateTime.fromISO('2025-12-25').toFormat('MMMM dd, yyyy')}}

String Manipulation

// Substring
{{$json.email.substring(0, 5)}}

// Replace
{{$json.message.replace('old', 'new')}}

// Split and join
{{$json.tags.split(',').join(', ')}}

5. Expression Helpers

String:

• .toLowerCase(), .toUpperCase()
• .trim(), .replace(), .substring()
• .split(), .includes()

Array:

• .length, .map(), .filter()
• .find(), .join(), .slice()

DateTime (Luxon):

• .toFormat(), .toISO(), .toLocal()
• .plus(), .minus(), .set()

Number:

• .toFixed(), .toString()
• Math operations: +, -, *, /, %

Examples

Webhook, HTTP-to-email, and timestamp examples follow.

Example 1: Webhook to Slack

Webhook receives:

{
  "body": {
    "name": "John Doe",
    "email": "john@example.com",
    "message": "Hello!"
  }
}

In Slack node text field:

New form submission!

Name: {{$json.body.name}}
Email: {{$json.body.email}}
Message: {{$json.body.message}}

Example 2: HTTP Request to Email

HTTP Request returns:

{
  "data": {
    "items": [
      {"name": "Product 1", "price": 29.99}
    ]
  }
}

In Email node (reference HTTP Request):

Product: {{$node["HTTP Request"].json.data.items[0].name}}
Price: ${{$node["HTTP Request"].json.data.items[0].price}}

Example 3: Format Timestamp

// Current date
{{$now.toFormat('yyyy-MM-dd')}}
// Result: 2025-10-20

// Time
{{$now.toFormat('HH:mm:ss')}}
// Result: 14:30:45

// Full datetime
{{$now.toFormat('yyyy-MM-dd HH:mm')}}
// Result: 2025-10-20 14:30

Pitfalls

Use this section when troubleshooting expression errors.

🚨 CRITICAL: Webhook Data Structure

Most Common Mistake: Webhook data is NOT at the root! Webhook node wraps incoming data under .body property to preserve headers, params, and query parameters.

❌ WRONG: {{$json.name}}
❌ WRONG: {{$json.email}}

✅ CORRECT: {{$json.body.name}}
✅ CORRECT: {{$json.body.email}}
✅ CORRECT: {{$json.body.message}}

When NOT to Use Expressions

Code Nodes

Code nodes use direct JavaScript access, NOT expressions!

// ❌ WRONG in Code node
const email = '={{$json.email}}';
const name = '{{$json.body.name}}';

// ✅ CORRECT in Code node
const email = $json.email;
const name = $json.body.name;

// Or using Code node API
const email = $input.item.json.email;
const allItems = $input.all();

Webhook Paths

// ❌ WRONG
path: "{{$json.user_id}}/webhook"

// ✅ CORRECT
path: "user-webhook"  // Static paths only

Credential Fields

// ❌ WRONG
apiKey: "={{$env.API_KEY}}"

// ✅ CORRECT
Use n8n credential system, not expressions

Validation Rules

1. Always Use {{}}: Expressions must be wrapped in double curly braces.
2. Use Quotes for Spaces: Field or node names with spaces require bracket notation.
3. Match Exact Node Names: Node references are case-sensitive.
4. No Nested {{}}: Don't double-wrap expressions.

Quick Fixes

Verification

Test in Expression Editor

1. Click field with expression
2. Open expression editor (click "fx" icon)
3. See live preview of result
4. Check for errors highlighted in red

Common Error Messages

"Cannot read property 'X' of undefined" → Parent object doesn't exist → Check your data path

"X is not a function" → Trying to call method on non-function → Check variable type

Expression shows as literal text → Missing {{ }} → Add curly braces

Related Skills

• n8n MCP Tools Expert: Learn how to validate expressions using MCP tools
• n8n Workflow Patterns: See expressions in real workflow examples
• n8n Node Configuration: Understand when expressions are needed

Limitations

• Use this skill only when the task clearly matches the scope described above.
• Do not treat the output as a substitute for environment-specific validation, testing, or expert review.
• Stop and ask for clarification if required inputs, permissions, safety boundaries, or success criteria are missing.