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, or working with webhook data in workflows.
risk: critical
source: community
date_added: "2026-03-06"
---

# n8n Expression Syntax

Expert guide for writing correct n8n expressions in workflows.

## Execution and data scope

EXAMPLES.md and COMMON_MISTAKES.md referenced below/in the guide are not bundled. `$json` in expression parameters represents the current input item, not a completed current node output; inspect actual execution data and item linking before referencing another node. Code-node APIs differ between per-item and all-items modes. Use credentials for secrets: the guide's `$env` examples can expose values and may be disabled. Avoid putting secrets/personal webhook data into messages or logs. Encode URL path/query components, guard missing arrays/objects and validate untrusted values before downstream actions. Test expressions with synthetic input; preview success is not authorization to send Slack/email messages.

## Detailed Guide

Read [the detailed guide](references/detailed-guide.md) before executing this skill. It retains the complete procedure and reference material. Treat its safety, prerequisites, and validation requirements as mandatory. For focused work, load the relevant sections; for end-to-end work, read the guide completely.

## 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.

---

## When NOT to Use Expressions

### ❌ Code Nodes

Code nodes use **direct JavaScript access**, NOT expressions!

```javascript
// ❌ 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

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

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

### ❌ Credential Fields

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

// ✅ CORRECT
Use n8n credential system, not expressions
```

---

## Working Examples

For real workflow examples, see EXAMPLES.md

### Example 1: Webhook to Slack

**Webhook receives**:
```json
{
  "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**:
```json
{
  "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

```javascript
// 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
```

---

## 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.