Help us improve
Share bugs, ideas, or general feedback.
From aeo-n8n
Master n8n's double-curly-brace expression language for dynamic workflow data. Covers $json, $node, and $input variable access patterns, debugging syntax issues, and handling webhook payloads. Activate when crafting expressions, resolving evaluation failures, or mapping data between nodes.
npx claudepluginhub aeyeops/aeo-skill-marketplace --plugin aeo-n8nHow this skill is triggered — by the user, by Claude, or both
Slash command
/aeo-n8n:n8n-expression-syntaxThe summary Claude sees in its skill listing — used to decide when to auto-load this skill
Expert guide for writing correct n8n expressions in workflows.
Validates n8n expression syntax and fixes errors in {{}} expressions, $json/$node access, webhook data ($json.body), and common patterns for workflows.
Validates n8n expression syntax and fixes common errors like incorrect {{}} braces, $json/$node access, webhook body referencing, and data mapping between nodes.
Validates n8n expression syntax with {{}}, $json, $node variables, and fixes errors like incorrect webhook data access under .body. Use for writing dynamic values or debugging workflow expressions.
Share bugs, ideas, or general feedback.
Expert guide for writing correct n8n expressions in workflows.
All dynamic content in n8n uses double curly braces:
{{expression}}
Examples:
✅ {{$json.email}}
✅ {{$json.body.name}}
✅ {{$node["HTTP Request"].json.data}}
❌ $json.email (no braces - treated as literal text)
❌ {$json.email} (single braces - invalid)
Access data from the current node:
{{$json.fieldName}}
{{$json['field with spaces']}}
{{$json.nested.property}}
{{$json.items[0].name}}
Access data from any previous node:
{{$node["Node Name"].json.fieldName}}
{{$node["HTTP Request"].json.data}}
{{$node["Webhook"].json.body.email}}
Important:
Access current date/time:
{{$now}}
{{$now.toFormat('yyyy-MM-dd')}}
{{$now.toFormat('HH:mm:ss')}}
{{$now.plus({days: 7})}}
Access environment variables:
{{$env.API_KEY}}
{{$env.DATABASE_URL}}
Most Common Mistake: Webhook data is NOT at the root!
{
"headers": {...},
"params": {...},
"query": {...},
"body": { // ⚠️ USER DATA IS HERE!
"name": "John",
"email": "john@example.com",
"message": "Hello"
}
}
❌ WRONG: {{$json.name}}
❌ WRONG: {{$json.email}}
✅ CORRECT: {{$json.body.name}}
✅ CORRECT: {{$json.body.email}}
✅ CORRECT: {{$json.body.message}}
Why: Webhook node wraps incoming data under .body property to preserve headers, params, and query parameters.
// Simple nesting
{{$json.user.email}}
// Array access
{{$json.data[0].name}}
{{$json.items[0].id}}
// Bracket notation for spaces
{{$json['field name']}}
{{$json['user data']['first name']}}
// Node without spaces
{{$node["Set"].json.value}}
// Node with spaces (common!)
{{$node["HTTP Request"].json.data}}
{{$node["Respond to Webhook"].json.message}}
// Webhook node
{{$node["Webhook"].json.body.email}}
// Concatenation (automatic)
Hello {{$json.body.name}}!
// In URLs
https://api.example.com/users/{{$json.body.user_id}}
// In object properties
{
"name": "={{$json.body.name}}",
"email": "={{$json.body.email}}"
}
Code nodes use direct JavaScript access, NOT expressions!
// ❌ WRONG in Code node
const email = '={{$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 = $input.all();
// ❌ WRONG
path: "{{$json.user_id}}/webhook"
// ✅ CORRECT
path: "user-webhook" // Static paths only
// ❌ WRONG
apiKey: "={{$env.API_KEY}}"
// ✅ CORRECT
Use n8n credential system, not expressions
Expressions must be wrapped in double curly braces.
❌ $json.field
✅ {{$json.field}}
Field or node names with spaces require bracket notation:
❌ {{$json.field name}}
✅ {{$json['field name']}}
❌ {{$node.HTTP Request.json}}
✅ {{$node["HTTP Request"].json}}
Node references are case-sensitive:
❌ {{$node["http request"].json}} // lowercase
❌ {{$node["Http Request"].json}} // wrong case
✅ {{$node["HTTP Request"].json}} // exact match
Don't double-wrap expressions:
❌ {{{$json.field}}}
✅ {{$json.field}}
For complete error catalog with fixes, see COMMON_MISTAKES.md
| Mistake | Fix |
|---|---|
$json.field | {{$json.field}} |
{{$json.field name}} | {{$json['field name']}} |
{{$node.HTTP Request}} | {{$node["HTTP Request"]}} |
{{{$json.field}}} | {{$json.field}} |
{{$json.name}} (webhook) | {{$json.body.name}} |
'={{$json.email}}' (Code node) | $json.email |
For real workflow examples, see EXAMPLES.md
Webhook receives:
{
"body": {
"name": "John Doe",
"email": "john@example.com",
"message": "Hello!"
}
}
In Slack node text field:
New form submission!
Name: {{$json.body.name}}
Email: {{$json.body.email}}
Message: {{$json.body.message}}
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}}
// Current date
{{$now.toFormat('yyyy-MM-dd')}}
// Result: 2025-10-20
// Time
{{$now.toFormat('HH:mm:ss')}}
// Result: 14:30:45
// Full datetime
{{$now.toFormat('yyyy-MM-dd HH:mm')}}
// Result: 2025-10-20 14:30
// First item
{{$json.users[0].email}}
// Array length
{{$json.users.length}}
// Last item
{{$json.users[$json.users.length - 1].name}}
// Dot notation (no spaces)
{{$json.user.email}}
// Bracket notation (with spaces or dynamic)
{{$json['user data'].email}}
// Concatenation (automatic)
Hello {{$json.name}}!
// String methods
{{$json.email.toLowerCase()}}
{{$json.name.toUpperCase()}}
// Direct use
{{$json.price}}
// Math operations
{{$json.price * 1.1}} // Add 10%
{{$json.quantity + 5}}
// Ternary operator
{{$json.status === 'active' ? 'Active User' : 'Inactive User'}}
// Default values
{{$json.email || 'no-email@example.com'}}
// Add days
{{$now.plus({days: 7}).toFormat('yyyy-MM-dd')}}
// Subtract hours
{{$now.minus({hours: 24}).toISO()}}
// Set specific date
{{DateTime.fromISO('2025-12-25').toFormat('MMMM dd, yyyy')}}
// Substring
{{$json.email.substring(0, 5)}}
// Replace
{{$json.message.replace('old', 'new')}}
// Split and join
{{$json.tags.split(',').join(', ')}}
"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
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()+, -, *, /, %.bodyEssential Rules:
.bodyMost Common Mistakes:
{{$json.name}} in webhooks → Use {{$json.body.name}}{{$json.email}} in Code → Use $json.email{{$node.HTTP Request}} → Use {{$node["HTTP Request"]}}For more details, see:
Need Help? Reference the n8n expression documentation or use n8n-mcp validation tools to check your expressions.