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skills/n8n-validation-expert/ERROR_CATALOG.md

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+# Error Catalog
+
+Comprehensive catalog of n8n validation errors with real examples and fixes.
+
+---
+
+## Error Types Overview
+
+Common validation errors by priority:
+
+| Error Type | Priority | Severity | Auto-Fix |
+|---|---|---|---|
+| missing_required | Highest | Error | ❌ |
+| invalid_value | High | Error | ❌ |
+| type_mismatch | Medium | Error | ❌ |
+| invalid_expression | Medium | Error | ❌ |
+| invalid_reference | Low | Error | ❌ |
+| operator_structure | Lowest | Warning | ✅ |
+
+---
+
+## Errors (Must Fix)
+
+### 1. missing_required
+
+**What it means**: Required field is not provided in node configuration
+
+**When it occurs**:
+- Creating new nodes without all required fields
+- Copying configurations between different operations
+- Switching operations that have different requirements
+
+**Most common validation error**
+
+#### Example 1: Slack Channel Missing
+
+**Error**:
+```json
+{
+  "type": "missing_required",
+  "property": "channel",
+  "message": "Channel name is required",
+  "node": "Slack",
+  "path": "parameters.channel"
+}
+```
+
+**Broken Configuration**:
+```javascript
+{
+  "resource": "message",
+  "operation": "post"
+  // Missing: channel
+}
+```
+
+**Fix**:
+```javascript
+{
+  "resource": "message",
+  "operation": "post",
+  "channel": "#general"  // ✅ Added required field
+}
+```
+
+**How to identify required fields**:
+```javascript
+// Use get_node_essentials to see what's required
+const info = get_node_essentials({
+  nodeType: "nodes-base.slack"
+});
+// Check properties marked as "required": true
+```
+
+#### Example 2: HTTP Request Missing URL
+
+**Error**:
+```json
+{
+  "type": "missing_required",
+  "property": "url",
+  "message": "URL is required for HTTP Request",
+  "node": "HTTP Request",
+  "path": "parameters.url"
+}
+```
+
+**Broken Configuration**:
+```javascript
+{
+  "method": "GET",
+  "authentication": "none"
+  // Missing: url
+}
+```
+
+**Fix**:
+```javascript
+{
+  "method": "GET",
+  "authentication": "none",
+  "url": "https://api.example.com/data"  // ✅ Added
+}
+```
+
+#### Example 3: Database Query Missing Connection
+
+**Error**:
+```json
+{
+  "type": "missing_required",
+  "property": "query",
+  "message": "SQL query is required",
+  "node": "Postgres",
+  "path": "parameters.query"
+}
+```
+
+**Broken Configuration**:
+```javascript
+{
+  "operation": "executeQuery"
+  // Missing: query
+}
+```
+
+**Fix**:
+```javascript
+{
+  "operation": "executeQuery",
+  "query": "SELECT * FROM users WHERE active = true"  // ✅ Added
+}
+```
+
+#### Example 4: Conditional Fields
+
+**Error**:
+```json
+{
+  "type": "missing_required",
+  "property": "body",
+  "message": "Request body is required when sendBody is true",
+  "node": "HTTP Request",
+  "path": "parameters.body"
+}
+```
+
+**Broken Configuration**:
+```javascript
+{
+  "method": "POST",
+  "url": "https://api.example.com/create",
+  "sendBody": true
+  // Missing: body (required when sendBody=true)
+}
+```
+
+**Fix**:
+```javascript
+{
+  "method": "POST",
+  "url": "https://api.example.com/create",
+  "sendBody": true,
+  "body": {
+    "contentType": "json",
+    "content": {
+      "name": "John",
+      "email": "john@example.com"
+    }
+  }  // ✅ Added conditional required field
+}
+```
+
+---
+
+### 2. invalid_value
+
+**What it means**: Provided value doesn't match allowed options or format
+
+**When it occurs**:
+- Using wrong enum value
+- Typos in operation names
+- Invalid format for specialized fields (emails, URLs, channels)
+
+**Second most common error**
+
+#### Example 1: Invalid Operation
+
+**Error**:
+```json
+{
+  "type": "invalid_value",
+  "property": "operation",
+  "message": "Operation must be one of: post, update, delete, get",
+  "current": "send",
+  "allowed": ["post", "update", "delete", "get"]
+}
+```
+
+**Broken Configuration**:
+```javascript
+{
+  "resource": "message",
+  "operation": "send"  // ❌ Invalid - should be "post"
+}
+```
+
+**Fix**:
+```javascript
+{
+  "resource": "message",
+  "operation": "post"  // ✅ Use valid operation
+}
+```
+
+#### Example 2: Invalid HTTP Method
+
+**Error**:
+```json
+{
+  "type": "invalid_value",
+  "property": "method",
+  "message": "Method must be one of: GET, POST, PUT, PATCH, DELETE, HEAD, OPTIONS",
+  "current": "FETCH",
+  "allowed": ["GET", "POST", "PUT", "PATCH", "DELETE", "HEAD", "OPTIONS"]
+}
+```
+
+**Broken Configuration**:
+```javascript
+{
+  "method": "FETCH",  // ❌ Invalid
+  "url": "https://api.example.com"
+}
+```
+
+**Fix**:
+```javascript
+{
+  "method": "GET",  // ✅ Use valid HTTP method
+  "url": "https://api.example.com"
+}
+```
+
+#### Example 3: Invalid Channel Format
+
+**Error**:
+```json
+{
+  "type": "invalid_value",
+  "property": "channel",
+  "message": "Channel name must start with # and be lowercase (e.g., #general)",
+  "current": "General"
+}
+```
+
+**Broken Configuration**:
+```javascript
+{
+  "resource": "message",
+  "operation": "post",
+  "channel": "General"  // ❌ Wrong format
+}
+```
+
+**Fix**:
+```javascript
+{
+  "resource": "message",
+  "operation": "post",
+  "channel": "#general"  // ✅ Correct format
+}
+```
+
+#### Example 4: Invalid Enum with Case Sensitivity
+
+**Error**:
+```json
+{
+  "type": "invalid_value",
+  "property": "resource",
+  "message": "Resource must be one of: channel, message, user, file",
+  "current": "Message",
+  "allowed": ["channel", "message", "user", "file"]
+}
+```
+
+**Note**: Enums are case-sensitive!
+
+**Broken Configuration**:
+```javascript
+{
+  "resource": "Message",  // ❌ Capital M
+  "operation": "post"
+}
+```
+
+**Fix**:
+```javascript
+{
+  "resource": "message",  // ✅ Lowercase
+  "operation": "post"
+}
+```
+
+---
+
+### 3. type_mismatch
+
+**What it means**: Value is wrong data type (string instead of number, etc.)
+
+**When it occurs**:
+- Hardcoding values that should be numbers
+- Using expressions where literals are expected
+- JSON serialization issues
+
+**Common error**
+
+#### Example 1: String Instead of Number
+
+**Error**:
+```json
+{
+  "type": "type_mismatch",
+  "property": "limit",
+  "message": "Expected number, got string",
+  "expected": "number",
+  "current": "100"
+}
+```
+
+**Broken Configuration**:
+```javascript
+{
+  "operation": "executeQuery",
+  "query": "SELECT * FROM users",
+  "limit": "100"  // ❌ String
+}
+```
+
+**Fix**:
+```javascript
+{
+  "operation": "executeQuery",
+  "query": "SELECT * FROM users",
+  "limit": 100  // ✅ Number
+}
+```
+
+#### Example 2: Number Instead of String
+
+**Error**:
+```json
+{
+  "type": "type_mismatch",
+  "property": "channel",
+  "message": "Expected string, got number",
+  "expected": "string",
+  "current": 12345
+}
+```
+
+**Broken Configuration**:
+```javascript
+{
+  "resource": "message",
+  "operation": "post",
+  "channel": 12345  // ❌ Number (even if channel ID)
+}
+```
+
+**Fix**:
+```javascript
+{
+  "resource": "message",
+  "operation": "post",
+  "channel": "#general"  // ✅ String (channel name, not ID)
+}
+```
+
+#### Example 3: Boolean as String
+
+**Error**:
+```json
+{
+  "type": "type_mismatch",
+  "property": "sendHeaders",
+  "message": "Expected boolean, got string",
+  "expected": "boolean",
+  "current": "true"
+}
+```
+
+**Broken Configuration**:
+```javascript
+{
+  "method": "GET",
+  "url": "https://api.example.com",
+  "sendHeaders": "true"  // ❌ String "true"
+}
+```
+
+**Fix**:
+```javascript
+{
+  "method": "GET",
+  "url": "https://api.example.com",
+  "sendHeaders": true  // ✅ Boolean true
+}
+```
+
+#### Example 4: Object Instead of Array
+
+**Error**:
+```json
+{
+  "type": "type_mismatch",
+  "property": "tags",
+  "message": "Expected array, got object",
+  "expected": "array",
+  "current": {"tag": "important"}
+}
+```
+
+**Broken Configuration**:
+```javascript
+{
+  "name": "New Channel",
+  "tags": {"tag": "important"}  // ❌ Object
+}
+```
+
+**Fix**:
+```javascript
+{
+  "name": "New Channel",
+  "tags": ["important", "alerts"]  // ✅ Array
+}
+```
+
+---
+
+### 4. invalid_expression
+
+**What it means**: n8n expression has syntax errors or invalid references
+
+**When it occurs**:
+- Missing `{{}}` around expressions
+- Typos in variable names
+- Referencing non-existent nodes or fields
+- Invalid JavaScript syntax in expressions
+
+**Moderately common**
+
+**Related**: See **n8n Expression Syntax** skill for comprehensive expression guidance
+
+#### Example 1: Missing Curly Braces
+
+**Error**:
+```json
+{
+  "type": "invalid_expression",
+  "property": "text",
+  "message": "Expressions must be wrapped in {{}}",
+  "current": "$json.name"
+}
+```
+
+**Broken Configuration**:
+```javascript
+{
+  "resource": "message",
+  "operation": "post",
+  "channel": "#general",
+  "text": "$json.name"  // ❌ Missing {{}}
+}
+```
+
+**Fix**:
+```javascript
+{
+  "resource": "message",
+  "operation": "post",
+  "channel": "#general",
+  "text": "={{$json.name}}"  // ✅ Wrapped in {{}}
+}
+```
+
+#### Example 2: Invalid Node Reference
+
+**Error**:
+```json
+{
+  "type": "invalid_expression",
+  "property": "value",
+  "message": "Referenced node 'HTTP Requets' does not exist",
+  "current": "={{$node['HTTP Requets'].json.data}}"
+}
+```
+
+**Broken Configuration**:
+```javascript
+{
+  "field": "data",
+  "value": "={{$node['HTTP Requets'].json.data}}"  // ❌ Typo in node name
+}
+```
+
+**Fix**:
+```javascript
+{
+  "field": "data",
+  "value": "={{$node['HTTP Request'].json.data}}"  // ✅ Correct node name
+}
+```
+
+#### Example 3: Invalid Property Access
+
+**Error**:
+```json
+{
+  "type": "invalid_expression",
+  "property": "text",
+  "message": "Cannot access property 'user' of undefined",
+  "current": "={{$json.data.user.name}}"
+}
+```
+
+**Broken Configuration**:
+```javascript
+{
+  "text": "={{$json.data.user.name}}"  // ❌ Structure doesn't exist
+}
+```
+
+**Fix** (with safe navigation):
+```javascript
+{
+  "text": "={{$json.data?.user?.name || 'Unknown'}}"  // ✅ Safe navigation + fallback
+}
+```
+
+#### Example 4: Webhook Data Access Error
+
+**Error**:
+```json
+{
+  "type": "invalid_expression",
+  "property": "value",
+  "message": "Property 'email' not found in $json",
+  "current": "={{$json.email}}"
+}
+```
+
+**Common Gotcha**: Webhook data is under `.body`!
+
+**Broken Configuration**:
+```javascript
+{
+  "field": "email",
+  "value": "={{$json.email}}"  // ❌ Missing .body
+}
+```
+
+**Fix**:
+```javascript
+{
+  "field": "email",
+  "value": "={{$json.body.email}}"  // ✅ Webhook data under .body
+}
+```
+
+---
+
+### 5. invalid_reference
+
+**What it means**: Configuration references a node that doesn't exist in the workflow
+
+**When it occurs**:
+- Node was renamed or deleted
+- Typo in node name
+- Copy-pasting from another workflow
+
+**Less common error**
+
+#### Example 1: Deleted Node Reference
+
+**Error**:
+```json
+{
+  "type": "invalid_reference",
+  "property": "expression",
+  "message": "Node 'Transform Data' does not exist in workflow",
+  "referenced_node": "Transform Data"
+}
+```
+
+**Broken Configuration**:
+```javascript
+{
+  "value": "={{$node['Transform Data'].json.result}}"  // ❌ Node deleted
+}
+```
+
+**Fix**:
+```javascript
+// Option 1: Update to existing node
+{
+  "value": "={{$node['Set'].json.result}}"
+}
+
+// Option 2: Remove expression if not needed
+{
+  "value": "default_value"
+}
+```
+
+#### Example 2: Connection to Non-Existent Node
+
+**Error**:
+```json
+{
+  "type": "invalid_reference",
+  "message": "Connection references node 'Slack1' which does not exist",
+  "source": "HTTP Request",
+  "target": "Slack1"
+}
+```
+
+**Fix**: Use `cleanStaleConnections` operation:
+```javascript
+n8n_update_partial_workflow({
+  id: "workflow-id",
+  operations: [{
+    type: "cleanStaleConnections"
+  }]
+})
+```
+
+#### Example 3: Renamed Node Not Updated
+
+**Error**:
+```json
+{
+  "type": "invalid_reference",
+  "property": "expression",
+  "message": "Node 'Get Weather' does not exist (did you mean 'Weather API'?)",
+  "referenced_node": "Get Weather",
+  "suggestions": ["Weather API"]
+}
+```
+
+**Broken Configuration**:
+```javascript
+{
+  "value": "={{$node['Get Weather'].json.temperature}}"  // ❌ Old name
+}
+```
+
+**Fix**:
+```javascript
+{
+  "value": "={{$node['Weather API'].json.temperature}}"  // ✅ Current name
+}
+```
+
+---
+
+## Warnings (Should Fix)
+
+### 6. best_practice
+
+**What it means**: Configuration works but doesn't follow best practices
+
+**Severity**: Warning (doesn't block execution)
+
+**When acceptable**: Development, testing, simple workflows
+
+**When to fix**: Production workflows, critical operations
+
+#### Example 1: Missing Error Handling
+
+**Warning**:
+```json
+{
+  "type": "best_practice",
+  "property": "onError",
+  "message": "Slack API can have rate limits and connection issues",
+  "suggestion": "Add error handling: onError: 'continueRegularOutput'"
+}
+```
+
+**Current Configuration**:
+```javascript
+{
+  "resource": "message",
+  "operation": "post",
+  "channel": "#alerts"
+  // No error handling ⚠️
+}
+```
+
+**Recommended Fix**:
+```javascript
+{
+  "resource": "message",
+  "operation": "post",
+  "channel": "#alerts",
+  "continueOnFail": true,
+  "retryOnFail": true,
+  "maxTries": 3
+}
+```
+
+#### Example 2: No Retry Logic
+
+**Warning**:
+```json
+{
+  "type": "best_practice",
+  "property": "retryOnFail",
+  "message": "External API calls should retry on failure",
+  "suggestion": "Add retryOnFail: true, maxTries: 3, waitBetweenTries: 1000"
+}
+```
+
+**When to ignore**: Idempotent operations, APIs with their own retry logic
+
+**When to fix**: Flaky external services, production automation
+
+---
+
+### 7. deprecated
+
+**What it means**: Using old API version or deprecated feature
+
+**Severity**: Warning (still works but may stop working in future)
+
+**When to fix**: Always (eventually)
+
+#### Example 1: Old typeVersion
+
+**Warning**:
+```json
+{
+  "type": "deprecated",
+  "property": "typeVersion",
+  "message": "typeVersion 1 is deprecated for Slack node, use version 2",
+  "current": 1,
+  "recommended": 2
+}
+```
+
+**Fix**:
+```javascript
+{
+  "type": "n8n-nodes-base.slack",
+  "typeVersion": 2,  // ✅ Updated
+  // May need to update configuration for new version
+}
+```
+
+---
+
+### 8. performance
+
+**What it means**: Configuration may cause performance issues
+
+**Severity**: Warning
+
+**When to fix**: High-volume workflows, large datasets
+
+#### Example 1: Unbounded Query
+
+**Warning**:
+```json
+{
+  "type": "performance",
+  "property": "query",
+  "message": "SELECT without LIMIT can return massive datasets",
+  "suggestion": "Add LIMIT clause or use pagination"
+}
+```
+
+**Current**:
+```sql
+SELECT * FROM users WHERE active = true
+```
+
+**Fix**:
+```sql
+SELECT * FROM users WHERE active = true LIMIT 1000
+```
+
+---
+
+## Auto-Sanitization Fixes
+
+### 9. operator_structure
+
+**What it means**: IF/Switch operator structure issues
+
+**Severity**: Warning
+
+**Auto-Fix**: ✅ YES - Fixed automatically on workflow save
+
+**Rare** (mostly auto-fixed)
+
+#### Fixed Automatically: Binary Operators
+
+**Before** (you create this):
+```javascript
+{
+  "type": "boolean",
+  "operation": "equals",
+  "singleValue": true  // ❌ Wrong for binary operator
+}
+```
+
+**After** (auto-sanitization fixes it):
+```javascript
+{
+  "type": "boolean",
+  "operation": "equals"
+  // singleValue removed ✅
+}
+```
+
+**You don't need to do anything** - this is fixed on save!
+
+#### Fixed Automatically: Unary Operators
+
+**Before**:
+```javascript
+{
+  "type": "boolean",
+  "operation": "isEmpty"
+  // Missing singleValue ❌
+}
+```
+
+**After**:
+```javascript
+{
+  "type": "boolean",
+  "operation": "isEmpty",
+  "singleValue": true  // ✅ Added automatically
+}
+```
+
+**What you should do**: Trust auto-sanitization, don't manually fix these!
+
+---
+
+## Recovery Patterns
+
+### Pattern 1: Progressive Validation
+
+**Problem**: Too many errors at once
+
+**Solution**:
+```javascript
+// Step 1: Minimal valid config
+let config = {
+  resource: "message",
+  operation: "post",
+  channel: "#general",
+  text: "Hello"
+};
+
+validate_node_operation({nodeType: "nodes-base.slack", config});
+// ✅ Valid
+
+// Step 2: Add features one by one
+config.attachments = [...];
+validate_node_operation({nodeType: "nodes-base.slack", config});
+
+config.blocks = [...];
+validate_node_operation({nodeType: "nodes-base.slack", config});
+```
+
+### Pattern 2: Error Triage
+
+**Problem**: Multiple errors
+
+**Solution**:
+```javascript
+const result = validate_node_operation({...});
+
+// 1. Fix errors (must fix)
+result.errors.forEach(error => {
+  console.log(`MUST FIX: ${error.property} - ${error.message}`);
+});
+
+// 2. Review warnings (should fix)
+result.warnings.forEach(warning => {
+  console.log(`SHOULD FIX: ${warning.property} - ${warning.message}`);
+});
+
+// 3. Consider suggestions (optional)
+result.suggestions.forEach(sug => {
+  console.log(`OPTIONAL: ${sug.message}`);
+});
+```
+
+### Pattern 3: Use get_node_essentials
+
+**Problem**: Don't know what's required
+
+**Solution**:
+```javascript
+// Before configuring, check requirements
+const info = get_node_essentials({
+  nodeType: "nodes-base.slack"
+});
+
+// Look for required fields
+info.properties.forEach(prop => {
+  if (prop.required) {
+    console.log(`Required: ${prop.name} (${prop.type})`);
+  }
+});
+```
+
+---
+
+## Summary
+
+**Most Common Errors**:
+1. `missing_required` (45%) - Always check get_node_essentials
+2. `invalid_value` (28%) - Check allowed values
+3. `type_mismatch` (12%) - Use correct data types
+4. `invalid_expression` (8%) - Use Expression Syntax skill
+5. `invalid_reference` (5%) - Clean stale connections
+
+**Auto-Fixed**:
+- `operator_structure` - Trust auto-sanitization!
+
+**Related Skills**:
+- **[SKILL.md](SKILL.md)** - Main validation guide
+- **[FALSE_POSITIVES.md](FALSE_POSITIVES.md)** - When to ignore warnings
+- **n8n Expression Syntax** - Fix expression errors
+- **n8n MCP Tools Expert** - Use validation tools correctly