/n8n-expression-syntax

name: n8n-expression-syntax
description: Validate n8n expression syntax and fix common errors. Use when writing n8n expressions, using {{}} syntax, accessing $json/$node variables, troubleshooting expression errors, mapping data between nodes, or referencing webhook data in workflows. Use this skill whenever configuring node fields that reference data from previous nodes — expressions are how n8n passes data between nodes, and getting the syntax wrong is the most common source of workflow errors. Also use when asked whether a complex expression hurts performance.

n8n Expression Syntax

Expert guide for writing correct n8n expressions in workflows.

---

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)

---

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

---

🚨 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": "john@example.com",
    "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.

---

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}}"
}

---

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

---

The transform gatekeeper

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

1. **The service's own node** does it in its own fields: a CRM node's field slots, the Slack node's Blocks field, a Data Table insert's per-column slots. HTTP Request only when no node covers the operation. 2. **A native node for the job.** Filter, IF / Switch, Summarize, Aggregate, Split Out, Merge, Compare Datasets, Remove Duplicates, Sort + Limit, Date & Time, XML / HTML / Extract From File, HTTP Request pagination, Crypto. The job-to-node table in `using-n8n-mcp-skills` maps jobs to nodes; their configs are in `n8n-node-configuration` → NATIVE_NODES.md. 3. **A short expression** (`{{ ... }}`) inside that node's field. Property access, method chains (`.map().filter().join()`), a ternary, string building, Luxon date math, the helper functions below — "take A, produce B" in one expression, without intermediate variables.

• **Querying nested JSON for one field** (pick, filter, sum inside an array) → `$jmespath()` in that same expression

(rules below). When downstream needs one item per element, use Split Out / Filter / Aggregate instead. 4. **Code node**, only for the closed list: loops or recursion no node expresses, state across runs, parsing no node handles, an allowlisted library, heavy all-items work (thousands of items, stated or measured), or one short Code node (~15 lines) replacing 4+ glue nodes. Give it a `Why Code:` note. See `n8n-code-javascript`.

**A function body is code.** When the logic needs `const`, `if`, `return` or several statements — an `(() => { ... })()` wrapped in `{{ }}` — it has outgrown an expression. Split i