n8n-validation-expert

by czlonkowski

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SKILL.md About

---
name: n8n-validation-expert
description: Interpret validation errors and guide fixing them. Use when encountering validation errors, validation warnings, false positives, operator structure issues, or need help understanding validation results. Also use when asking about validation profiles, error types, the validation loop process, or auto-fix capabilities. Consult this skill whenever a validate_node or validate_workflow call returns errors or warnings — it knows which warnings are false positives and which errors need real fixes.
---

# n8n Validation Expert

Expert guide for interpreting and fixing n8n validation errors.

---

## Validation Philosophy

**Validate early, validate often**

Validation is typically iterative:
- Expect validation feedback loops
- Usually 2-3 validate → fix cycles
- Average: 23s thinking about errors, 58s fixing them

**Key insight**: Validation is an iterative process, not one-shot!

---

## Error Severity Levels

### 1. Errors (Must Fix)
**Blocks workflow execution** - Must be resolved before activation

**Types**:
- `missing_required` - Required field not provided
- `invalid_value` - Value doesn't match allowed options
- `type_mismatch` - Wrong data type (string instead of number)
- `invalid_reference` - Referenced node doesn't exist
- `invalid_expression` - Expression syntax error

**Example**:
```json
{
  "type": "missing_required",
  "property": "channel",
  "message": "Channel name is required",
  "fix": "Provide a channel name (lowercase, no spaces, 1-80 characters)"
}
```

### 2. Warnings (Should Fix)
**Doesn't block execution** - Workflow can be activated but may have issues

**Types**:
- `best_practice` - Recommended but not required
- `deprecated` - Using old API/feature
- `performance` - Potential performance issue

**Example**:
```json
{
  "type": "best_practice",
  "property": "errorHandling",
  "message": "Slack API can have rate limits",
  "suggestion": "Add onError: 'continueRegularOutput' with retryOnFail"
}
```

### 3. Suggestions (Optional)
**Nice to have** - Improvements that could enhance workflow

**Types**:
- `optimization` - Could be more efficient
- `alternative` - Better way to achieve same result

---

## The Validation Loop

### Pattern from Telemetry
**7,841 occurrences** of this pattern:

```
1. Configure node
   ↓
2. validate_node (23 seconds thinking about errors)
   ↓
3. Read error messages carefully
   ↓
4. Fix errors
   ↓
5. validate_node again (58 seconds fixing)
   ↓
6. Repeat until valid (usually 2-3 iterations)
```

### Example
```javascript
// Iteration 1
let config = {
  resource: "channel",
  operation: "create"
};

const result1 = validate_node({
  nodeType: "nodes-base.slack",
  config,
  profile: "runtime"
});
// → Error: Missing "name"

// ⏱️  23 seconds thinking...

// Iteration 2
config.name = "general";

const result2 = validate_node({
  nodeType: "nodes-base.slack",
  config,
  profile: "runtime"
});
// → Error: Missing "text"

// ⏱️  58 seconds fixing...

// Iteration 3
config.text = "Hello!";

const result3 = validate_node({
  nodeType: "nodes-base.slack",
  config,
  profile: "runtime"
});
// → Valid! ✅
```

**This is normal!** Don't be discouraged by multiple iterations.

---

## Validation Profiles

Choose the right profile for your stage:

### minimal
**Use when**: Quick checks during editing

**Validates**:
- Only required fields
- Basic structure

**Pros**: Fastest, most permissive
**Cons**: May miss issues

### runtime (RECOMMENDED)
**Use when**: Pre-deployment validation

**Validates**:
- Required fields
- Value types
- Allowed values
- Basic dependencies

**Pros**: Balanced, catches real errors
**Cons**: Some edge cases missed

**This is the recommended profile for most use cases**

### ai-friendly
**Use when**: AI-generated configurations

**Validates**:
- Same as runtime
- Reduces false positives
- More tolerant of minor issues

**Pros**: Less noisy for AI workflows
**Cons**: May allow some questionable configs

### strict
**Use when**: Production deployment, critical workflows

**Validates**:
- Everything
- Best practices
- Performance concerns
- Security issues

**Pros**: Maximum safety
**Cons**: Many warnings, some false positives

---

## Common Error Types

### 1. missing_required
**What it means**: A required field is not provided

**How to fix**:
1. Use `get_node` to see required fields
2. Add the missing field to your configuration
3. Provide an appropriate value

**Example**:
```javascript
// Error
{
  "type": "missing_required",
  "property": "channel",
  "message": "Channel name is required"
}

// Fix
config.channel = "#general";
```

### 2. invalid_value
**What it means**: Value doesn't match allowed options

**How to fix**:
1. Check error message for allowed values
2. Use `get_node` to see options
3. Update to a valid value

**Example**:
```javascript
// Error
{
  "type": "invalid_value",
  "property": "operation",
  "message": "Operation must be one of: post, update, delete",
  "current": "send"
}

// Fix
config.operation = "post";  // Use valid operation
```

### 3. type_mismatch
**What it means**: Wrong data type for field

**How to fix**:
1. Check expected type in error message
2. Convert value to correct type

**Example**:
```javascript
// Error
{
  "type": "type_mismatch",
  "property": "limit",
  "message": "Expected number, got string",
  "current": "100"
}

// Fix
config.limit = 100;  // Number, not string
```

### 4. invalid_expression
**What it means**: Expression syntax error

**How to fix**:
1. Use n8n Expression Syntax skill
2. Check for missing `{{}}` or typos
3. Verify node/field references

**Example**:
```javascript
// Error
{
  "type": "invalid_expression",
  "property": "text",
  "message": "Invalid expression: $json.name",
  "current": "$json.name"
}

// Fix
config.text = "={{$json.name}}";  // Add {{}}
```

### 5. invalid_reference
**What it means**: Referenced node doesn't exist

**How to fix**:
1. Check node name spelling
2. Verify node exists in workflow
3. Update reference to correct name

**Example**:
```javascript
// Error
{
  "type": "invalid_reference",
  "property": "expression",
  "message": "Node 'HTTP Requets' does not exist",
  "current": "={{$node['HTTP Requets'].json.data}}"
}

// Fix - correct typo
config.expression = "={{$node['HTTP Request'].json.data}}";
```

### 6. patchNodeField Errors
**What it means**: A `patchNodeField` operation failed during `n8n_update_partial_workflow`

The `patchNodeField` operation is strict by design — it errors instead of silently continuing when something is wrong. This catches mistakes early but means you need to handle these specific error cases.

**Error: Find string not found**
The patch's `find` value doesn't exist in the target field. This usually means the content was already changed, or the find string has a typo.

```
patchNodeField: find string not found in field "parameters.jsCode"
```

**How to fix**: Double-check the exact string. Use `n8n_get_workflow` to inspect the current field value. Whitespace and line endings matter — if unsure, use `regex: true` with `\s+` for flexible whitespace matching.

**Error: Ambiguous match (multiple occurrences)**
The find string appears more than once in the field. Without `replaceAll: true`, this is treated as ambiguous and rejected.

```
patchNodeField: find string matches 3 times in field "parameters.jsCode" — set replaceAll: true to replace all, or use a more specific find string
```

**How to fix**: Either set `replaceAll: true` if you want to replace all occurrences, or make your find string more specific to match only the intended location.

**Error: Invalid regex pattern**
When `regex: true`, the pattern is validated for correctness and safety.

```
patchNodeField: invalid or unsafe regex pattern
```

**How to fix**: Check regex syntax. Nested quantifiers like `(a+)+` and overlapping alternations like `(\w|\d)+` are rejected as ReDoS risks. Simplify the pattern.

---

## Auto-Sanitization System

### What It Does
**Automatically fixes common operator structure issues** on ANY workflow update

**Runs when**:
- `n8n_create_workflow`
- `n8n_update_partial_workflow`
- Any workflow save operation

### What It Fixes

#### 1. Binary Operators (Two Values)
**Operators**: equals, notEquals, contains, notContains, greaterThan, lessThan, startsWith, endsWith

**Fix**: Removes `singleValue` property (binary operators compare two values)

**Before**:
```javascript
{
  "type": "boolean",
  "operation": "equals",
  "singleValue": true  // ❌ Wrong!
}
```

**After** (automatic):
```javascript
{
  "type": "boolean",
  "operation": "equals"
  // singleValue removed ✅
}
```

#### 2. Unary Operators (One Value)
**Operators**: isEmpty, isNotEmpty, true, false

**Fix**: Adds `singleValue: true` (unary operators check single value)

**Before**:
```javascript
{
  "type": "boolean",
  "operation": "isEmpty"
  // Missing singleValue ❌
}
```

**After** (automatic):
```javascript
{
  "type": "boolean",
  "operation": "isEmpty",
  "singleValue": true  // ✅ Added
}
```

#### 3. IF/Switch Metadata
**Fix**: Adds complete `conditions.options` metadata for IF v2.2+ and Switch v3.2+

### What It CANNOT Fix

#### 1. Broken Connections
References to non-existent nodes

**Solution**: Use `cleanStaleConnections` operation in `n8n_update_partial_workflow`

#### 2. Branch Count Mismatches
3 Switch rules but only 2 output connections

**Solution**: Add missing connections or remove extra rules

#### 3. Paradoxical Corrupt States
API returns corrupt data but rejects updates

**Solution**: May require manual database intervention

---

## False Positives

### What Are They?
Validation warnings that are technically "wrong" but acceptable in your use case

### Common False Positives

#### 1. "Missing error handling"
**Warning**: No error handling configured

**When acceptable**:
- Simple workflows where failures are obvious
- Testing/development workflows
- Non-critical notifications

**When to fix**: Production workflows handling important data

#### 2. "No retry logic"
**Warning**: Node doesn't retry on failure

**When acceptable**:
- APIs with their own retry logic
- Idempotent operations
- Manual trigger workflows

**When to fix**: Flaky external services, production automation

#### 3. "Missing rate limiting"
**Warning**: No rate limiting for API calls

**When acceptable**:
- Internal APIs with no limits
- Low-volume workflows
- APIs with server-side rate limiting

**When to fix**: Public APIs, high-volume workflows

#### 4. "Unbounded query"
**Warning**: SELECT without LIMIT

**When acceptable**:
- Small known datasets
- Aggregation queries
- Development/testing

**When to fix**: Production queries on large tables

### Reducing False Positives

**Use `ai-friendly` profile**:
```javascript
validate_node({
  nodeType: "nodes-base.slack",
  config: {...},
  profile: "ai-friendly"  // Fewer false positives
})
```

---

## Validation Result Structure

### Complete Response
```javascript
{
  "valid": false,
  "errors": [
    {
      "type": "missing_required",
      "property": "channel",
      "message": "Channel name is required",
      "fix": "Provide a channel name (lowercase, no spaces)"
    }
  ],
  "warnings": [
    {
      "type": "best_practice",
      "property": "errorHandling",
      "message": "Slack API can have rate limits",
      "suggestion": "Add onError: 'continueRegularOutput'"
    }
  ],
  "suggestions": [
    {
      "type": "optimization",
      "message": "Consider using batch operations for multiple messages"
    }
  ],
  "summary": {
    "hasErrors": true,
    "errorCount": 1,
    "warningCount": 1,
    "suggestionCount": 1
  }
}
```

### How to Read It

#### 1. Check `valid` field
```javascript
if (result.valid) {
  // ✅ Configuration is valid
} else {
  // ❌ Has errors - must fix before deployment
}
```

#### 2. Fix errors first
```javascript
result.errors.forEach(error => {
  console.log(`Error in ${error.property}: ${error.message}`);
  console.log(`Fix: ${error.fix}`);
});
```

#### 3. Review warnings
```javascript
result.warnings.forEach(warning => {
  console.log(`Warning: ${warning.message}`);
  console.log(`Suggestion: ${warning.suggestion}`);
  // Decide if you need to address this
});
```

#### 4. Consider suggestions
```javascript
// Optional improvements
// Not required but may enhance workflow
```

---

## Workflow Validation

### validate_workflow (Structure)
**Validates entire workflow**, not just individual nodes

**Checks**:
1. **Node configurations** - Each node valid
2. **Connections** - No broken references
3. **Expressions** - Syntax and references valid
4. **Flow** - Logical workflow structure

**Example**:
```javascript
validate_workflow({
  workflow: {
    nodes: [...],
    connections: {...}
  },
  options: {
    validateNodes: true,
    validateConnections: true,
    validateExpressions: true,
    profile: "runtime"
  }
})
```

### Common Workflow Errors

#### 1. Broken Connections
```json
{
  "error": "Connection from 'Transform' to 'NonExistent' - target node not found"
}
```

**Fix**: Remove stale connection or create missing node

#### 2. Circular Dependencies
```json
{
  "error": "Circular dependency detected: Node A → Node B → Node A"
}
```

**Fix**: Restructure workflow to remove loop

#### 3. Multiple Start Nodes
```json
{
  "warning": "Multiple trigger nodes found - only one will execute"
}
```

**Fix**: Remove extra triggers or split into separate workflows

#### 4. Disconnected Nodes
```json
{
  "warning": "Node 'Transform' is not connected to workflow flow"
}
```

**Fix**: Connect node or remove if unused

---

## Recovery Strategies

### Strategy 1: Start Fresh
**When**: Configuration is severely broken

**Steps**:
1. Note required fields from `get_node`
2. Create minimal valid configuration
3. Add features incrementally
4. Validate after each addition

### Strategy 2: Binary Search
**When**: Workflow validates but executes incorrectly

**Steps**:
1. Remove half the nodes
2. Validate and test
3. If works: problem is in removed nodes
4. If fails: problem is in remaining nodes
5. Repeat until problem isolated

### Strategy 3: Clean Stale Connections
**When**: "Node not found" errors

**Steps**:
```javascript
n8n_update_partial_workflow({
  id: "workflow-id",
  operations: [{
    type: "cleanStaleConnections"
  }]
})
```

### Strategy 4: Use Auto-fix
**When**: Validation errors that can be automatically resolved

**Steps**:
```javascript
// Preview fixes (default - doesn't apply)
n8n_autofix_workflow({
  id: "workflow-id",
  applyFixes: false,
  confidenceThreshold: "medium"  // high, medium, low
})

// Review fixes, then apply
n8n_autofix_workflow({
  id: "workflow-id",
  applyFixes: true
})
```

---

## Auto-Fix Capabilities

The `n8n_autofix_workflow` tool can fix these issue types:

1. **expression-format** - Missing `=` prefix in expressions (e.g., `{{ $json.field }}` → `={{ $json.field }}`)
2. **typeversion-correction** - Downgrades nodes with unsupported typeVersions
3. **error-output-config** - Removes conflicting onError settings
4. **node-type-correction** - Fixes unknown node types using similarity matching (90%+ confidence)
5. **webhook-missing-path** - Generates UUIDs for webhook nodes missing path configuration
6. **typeversion-upgrade** - Smart upgrades to latest node versions with auto-migration
7. **version-migration** - Guidance for complex breaking changes requiring manual steps

**Confidence levels**: `high` (90%+, safe to auto-apply), `medium` (70-89%, review recommended), `low` (<70%, manual review required)

```javascript
// Preview all fixes
n8n_autofix_workflow({id: "workflow-id"})

// Only apply high-confidence fixes
n8n_autofix_workflow({
  id: "workflow-id",
  applyFixes: true,
  confidenceThreshold: "high"
})

// Target specific fix types
n8n_autofix_workflow({
  id: "workflow-id",
  fixTypes: ["expression-format", "typeversion-upgrade"],
  applyFixes: true
})
```

**Post-update guidance**: For version upgrades, check the `postUpdateGuidance` field in the response for step-by-step migration instructions.

---

## Best Practices

### ✅ Do

- Validate after every significant change
- Read error messages completely
- Fix errors iteratively (one at a time)
- Use `runtime` profile for pre-deployment
- Check `valid` field before assuming success
- Trust auto-sanitization for operator issues
- Use `get_node` when unclear about requirements
- Document false positives you accept

### ❌ Don't

- Skip validation before activation
- Try to fix all errors at once
- Ignore error messages
- Use `strict` profile during development (too noisy)
- Assume validation passed (always check result)
- Manually fix auto-sanitization issues
- Deploy with unresolved errors
- Ignore all warnings (some are important!)

---

## Detailed Guides

For comprehensive error catalogs and false positive examples:

- **[ERROR_CATALOG.md](ERROR_CATALOG.md)** - Complete list of error types with examples
- **[FALSE_POSITIVES.md](FALSE_POSITIVES.md)** - When warnings are acceptable

---

## Summary

**Key Points**:
1. **Validation is iterative** (avg 2-3 cycles, 23s + 58s)
2. **Errors must be fixed**, warnings are optional
3. **Auto-sanitization** fixes operator structures automatically
4. **Use runtime profile** for balanced validation
5. **False positives exist** - learn to recognize them
6. **Read error messages** - they contain fix guidance

**Validation Process**:
1. Validate → Read errors → Fix → Validate again
2. Repeat until valid (usually 2-3 iterations)
3. Review warnings and decide if acceptable
4. Deploy with confidence

**Related Skills & Tools**:
- n8n MCP Tools Expert - Use validation tools correctly
- n8n Expression Syntax - Fix expression errors
- n8n Node Configuration - Understand required fields
- `n8n_audit_instance` - Proactive security validation (hardcoded secrets, unauthenticated webhooks, missing error handling, data retention)