n8n-expression-syntax

n8n Expression Syntax

Expert guide for writing correct n8n expressions in workflows.

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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)

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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}}

Warning: Some n8n instances have N8N_BLOCK_ENV_ACCESS_IN_NODE enabled, which blocks $env access entirely. If $env returns errors, use alternative approaches:

• Store values in credentials instead
• Use a Set node with manually entered values
• Pass values through webhook query parameters

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🚨 CRITICAL: Webhook Data Structure

Most Common Mistake: Webhook data is NOT at the root!

Webhook Node Output Structure

{
  "headers": {...},
  "params": {...},
  "query": {...},
  "body": {           // ⚠️ USER DATA IS HERE!
    "name": "John",
    "email": "[email protected]",
    "message": "Hello"
  }
}

Correct Webhook Data Access

❌ 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.

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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']}}

Reference Other Nodes

// 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}}

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}}"
}

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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

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The transform gatekeeper

Before you add any node — or write any code — to transform data, walk this order and stop at the first that fits:

1. Expression ({{ ... }}) in the consuming field. Property access, method chains (.map().filter().join()), ternaries, string building, Luxon date math — if it's "take A, produce B" without intermediate variables, it's an expression. This covers most "just transform this" cases.

2. Arrow-function IIFE inside an Edit Fields field. When the logic needs intermediate variables, branching, or comments but still operates on one item, wrap it in an immediately-invoked arrow function right in the field value:

   ={{ (() => {
       const items = $json.line_items;
       const subtotal = items.reduce((sum, it) => sum + it.price * it.qty, 0);
       const tax = subtotal * 0.08;
       return (subtotal + tax).toFixed(2);
   })() }}
   

   The outer (...) brackets the function; the trailing () invokes it. Drop either and n8n refuses to run. Inside you get the full expression scope ($json, $('Node'), $now, Luxon) plus const/let, if/switch, try/catch, and regex. No require, no await.

3. Code node — last resort. Only when you need multi-item aggregation across the whole dataset ($input.all()), an allowlisted library, or async work.

Why the order matters. It's not style — it's readability and performance. The Code node runs in a sandboxed VM with per-invocation setup and value marshaling — a cold-start cost that can reach 500–1000ms before your logic runs. (It amortizes on warm, high-item-count runs, so treat this as the common-case cost, not a universal constant.) The same logic in an expression or Edit Fields IIFE runs in-process in single-digit milliseconds and skips the sandbox entirely. For pure single-item shaping that's a large gap with no functional difference, and it compounds on hot paths like per-request webhooks. The expression also stays visible in the field that uses it, instead of hiding in an upstream node someone has to open to understand. Reach past a stage only when the input or scope genuinely demands it.

The Set-node antipattern and branch convergence

Delete Set nodes that feed one consumer

A Set / Edit Fields node whose only job is to extract a value and hand it to one downstream node is dead weight. Inline its expression at the consumer instead.

❌  Webhook → Set { customer_id: {{ $json.body.customer_id }} } → Postgres: WHERE id = {{ $json.customer_id }}

✅  Webhook → Postgres: WHERE id = {{ $('Webhook').item.json.body.customer_id }}

The Set node adds a hop, more canvas clutter, and a refactor hazard, while doing nothing the consumer couldn't do itself. To remove it cleanly with n8n_update_partial_workflow: rewire the connection (removeConnection from the Set's source-and-target, addConnection straight from source to consumer), patchNodeField the consumer's expression to reference the original source by node name, then removeNode the Set.

Quick test: count how many downstream nodes reference each field the Set produces.

• 0 or 1 → delete, inline at the consumer.
• 2+ → it may earn its place.

Legitimate exceptions — keep the Set when:

• 2+ consumers read the same derived value and the derivation is non-trivial (a name aids readability and you compute it once).
• It's a sub-workflow's final Return node, shaping the output contract. Here the "single consumer" is every caller, so the Set is the API boundary — and with Include Other Fields: false it whitelists the output shape so internal scratch fields don't leak.
• You're renaming or whitelisting fields and want that visible in one place rather than spread across consumer expressions.

Branch convergence: anchor with a NoOp

When branches converge (after IF/Switch/Merge), $json becomes "whichever branch fired last" — non-deterministic, and a silent source of wrong data. Insert a NoOp node at the convergence, name it descriptively (Combine Inputs), and have downstream nodes reference it by name:

Branch A ──┐
           ├─→ [NoOp: Combine Inputs] ──→ downstream uses $('Combine Inputs').item.json.x
Branch B ──┘

The NoOp survives refactors: inserting a transform later between it and the consumer doesn't break the $('Combine Inputs') reference. (If the branches produce different shapes, use a Set node instead of a NoOp to normalize both into one shape — see the exceptions above.)

More broadly in branchy flows, prefer $('Node').item.json.x over deep $json.x. $json breaks the moment an intermediate node is inserted or a node clears item context (Aggregate, Code with Run for All, branching merges); the failure is silent and downstream gets the wrong data with no error. A node-name reference is unambiguous regardless of what sits between source and consumer.

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Validation Rules

1. Always Use {{}}

Expressions must be wrapped in double curly braces.

❌ $json.field
✅ {{$json.field}}

2. Use Quotes for Spaces and Special Characters

Field or node names with spaces, diacritics, or special characters require bracket notation:

❌ {{$json.field name}}
✅ {{$json['field name']}}

❌ {{$node.HTTP Request.json}}
✅ {{$node["HTTP Request"].json}}

// Bracket notation is mandatory for keys with special characters
✅ {{$json['Gross Price w/o shipment']}}
✅ {{$json['Cena brutto zł']}}

3. Match Exact Node Names

Node references are case-sensitive:

❌ {{$node["http request"].json}}  // lowercase
❌ {{$node["Http Request"].json}}  // wrong case
✅ {{$node["HTTP Request"].json}}  // exact match

4. No Nested {{}}

Don't double-wrap expressions:

❌ {{{$json.field}}}
✅ {{$json.field}}

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Common Mistakes

For complete error catalog with fixes, see COMMON_MISTAKES.md

Quick Fixes

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

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Working Exampl

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