Input Validation at the Gate

The Problem

A payment processing workflow expects:

{ "userId": "user-123", "amount": 99.99, "currency": "USD" }

Instead it receives:

{ "userId": null, "amount": "ninety-nine", "currency": "USD" }

Without input validation:

• The payment node attempts to parse "ninety-nine" as a number — throws an unhandled exception
• The exception surfaces as a generic 500 error with no helpful context
• The audit log shows an error but not why the input was wrong
• The bug may have gone through integration testing unnoticed

The Solution

InputValidationGuard validates input against a JSON schema in the Pre phase. If validation fails and strictMode=true, the node never runs — the caller receives a structured error listing exactly which fields are wrong.

{
  "guardRails": {
    "individual": [
      {
        "name": "InputValidationGuard",
        "enabled": true,
        "order": 1,
        "config": {
          "schema": {
            "type": "object",
            "required": ["userId", "amount", "currency"],
            "properties": {
              "userId":   { "type": "string" },
              "amount":   { "type": "number" },
              "currency": { "type": "string" }
            }
          },
          "strictMode": true
        }
      }
    ]
  }
}

What the caller receives

{
  "IsAllowed": false,
  "ErrorMessage": "Input validation failed",
  "Metadata": {
    "validation_errors": [
      "Required field 'userId' is missing or null",
      "Field 'amount': expected 'number', got 'string'"
    ]
  }
}

strictMode vs Warning Mode

JSON Type Mapping

The guard maps CLR types to JSON schema types:

Combining Validation with PII Detection

Input validation and PII detection are complementary guards. Run validation first to ensure the payload structure is correct, then check for PII in the validated input:

"individual": [
  // Step 1: Validate structure
  { "name": "InputValidationGuard", "order": 1,
    "config": { "schema": {...}, "strictMode": true } },

  // Step 2: Check for PII in validated input
  { "name": "PiiDetectionGuard", "order": 2,
    "config": { "sensitivityLevel": "medium" } }
]

This order ensures that if the structure is wrong, the PII scanner never runs on malformed data — avoiding false positives from unexpected field positions.