n8n Expression Syntax
Expert guide for writing correct n8n expressions in workflows.
Purpose
Teaches correct n8n expression syntax ({{ }} patterns) and fixes common mistakes, especially the critical webhook data structure gotcha.
Activates On
- expression
- {{}} syntax
- $json, $node, $now, $env
- webhook data
- troubleshoot expression error
- undefined in workflow
File Count
4 files
Dependencies
n8n-mcp tools:
- None directly (syntax knowledge skill)
- Works with n8n-mcp validation tools
Related skills:
- n8n Workflow Patterns (uses expressions in examples)
- n8n MCP Tools Expert (validates expressions)
- n8n Node Configuration (when expressions are needed)
Coverage
Core Topics
- Expression format ({{ }})
- Core variables ($json, $node, $now, $env)
- Webhook data structure ($json.body.*)
- When NOT to use expressions (Code nodes)
Common Patterns
- Accessing nested fields
- Referencing other nodes
- Array and object access
- Date/time formatting
- String manipulation
Error Prevention
- 15 common mistakes with fixes
- Quick reference table
- Debugging process
Evaluations
4 scenarios (100% coverage expected):
- eval-001: Missing curly braces
- eval-002: Webhook body data access (critical!)
- eval-003: Code node vs expression confusion
- eval-004: Node reference syntax
Key Features
✅ Critical Gotcha Highlighted: Webhook data under .body
✅ Real Examples: From MCP testing and real templates
✅ Quick Fixes Table: Fast reference for common errors
✅ Code vs Expression: Clear distinction
✅ Comprehensive: Covers 95% of expression use cases
Files
- SKILL.md - Main content with all essential knowledge
- COMMON_MISTAKES.md - Complete error catalog with 15 common mistakes
- EXAMPLES.md - 10 real working examples
- README.md (this file) - Skill metadata
Success Metrics
Expected outcomes:
- Users correctly wrap expressions in {{ }}
- Zero webhook
.bodyaccess errors - No expressions used in Code nodes
- Correct $node reference syntax
Last Updated
2025-10-20
Part of: n8n-skills repository Conceived by: Romuald Członkowski - www.aiadvisors.pl/en