Argument Validator Generator

Generate comprehensive argument validation logic for CLI applications with type coercion and constraint checking.

Capabilities

• Generate type coercion functions for arguments
• Create custom validators with constraint checking
• Set up validation error messages
• Implement value normalization
• Configure mutually exclusive validation
• Generate validation schemas

Usage

Invoke this skill when you need to:

• Add type validation to CLI arguments
• Create custom argument validators
• Implement complex constraint checking
• Generate helpful validation error messages

Inputs

Parameter	Type	Required	Description
language	string	Yes	Target language (typescript, python, go, rust)
validators	array	Yes	List of validators to generate
outputPath	string	No	Output path for generated files

Validator Structure

{
  "validators": [
    {
      "name": "port",
      "type": "number",
      "constraints": {
        "min": 1,
        "max": 65535
      },
      "errorMessage": "Port must be between 1 and 65535"
    },
    {
      "name": "email",
      "type": "string",
      "pattern": "^[\\w.-]+@[\\w.-]+\\.\\w+$",
      "errorMessage": "Invalid email format"
    },
    {
      "name": "environment",
      "type": "enum",
      "values": ["development", "staging", "production"],
      "aliases": { "dev": "development", "prod": "production" }
    }
  ]
}

Generated Code Patterns

TypeScript Validators

import { z } from 'zod';

// Port validator
export const portSchema = z
  .number()
  .int()
  .min(1, 'Port must be at least 1')
  .max(65535, 'Port must be at most 65535');

export function validatePort(value: unknown): number {
  const parsed = typeof value === 'string' ? parseInt(value, 10) : value;
  return portSchema.parse(parsed);
}

// Email validator
export const emailSchema = z
  .string()
  .email('Invalid email format')
  .toLowerCase();

export function validateEmail(value: unknown): string {
  return emailSchema.parse(value);
}

// Environment enum with aliases
const envAliases: Record<string, string> = {
  dev: 'development',
  prod: 'production',
};

export const environmentSchema = z
  .string()
  .transform((val) => envAliases[val] || val)
  .pipe(z.enum(['development', 'staging', 'production']));

export function validateEnvironment(value: unknown): string {
  return environmentSchema.parse(value);
}

Python Validators

from typing import Any, List, Optional, Union
import re

class ValidationError(Exception):
    """Raised when validation fails."""
    pass

def validate_port(value: Any) -> int:
    """Validate port number."""
    try:
        port = int(value)
    except (TypeError, ValueError):
        raise ValidationError(f"Invalid port number: {value}")

    if not 1 <= port <= 65535:
        raise ValidationError("Port must be between 1 and 65535")

    return port

def validate_email(value: Any) -> str:
    """Validate email address."""
    if not isinstance(value, str):
        raise ValidationError(f"Email must be a string, got {type(value).__name__}")

    pattern = r'^[\w.-]+@[\w.-]+\.\w+$'
    if not re.match(pattern, value):
        raise ValidationError("Invalid email format")

    return value.lower()

ENV_ALIASES = {'dev': 'development', 'prod': 'production'}
VALID_ENVIRONMENTS = ['development', 'staging', 'production']

def validate_environment(value: Any) -> str:
    """Validate environment name."""
    if not isinstance(value, str):
        raise ValidationError(f"Environment must be a string")

    normalized = ENV_ALIASES.get(value, value)
    if normalized not in VALID_ENVIRONMENTS:
        raise ValidationError(
            f"Invalid environment: {value}. "
            f"Must be one of: {', '.join(VALID_ENVIRONMENTS)}"
        )

    return normalized

Go Validators

package validators

import (
    "fmt"
    "regexp"
    "strconv"
    "strings"
)

// ValidationError represents a validation failure
type ValidationError struct {
    Field   string
    Message string
}

func (e *ValidationError) Error() string {
    return fmt.Sprintf("%s: %s", e.Field, e.Message)
}

// ValidatePort validates a port number
func ValidatePort(value string) (int, error) {
    port, err := strconv.Atoi(value)
    if err != nil {
        return 0, &ValidationError{
            Field:   "port",
            Message: fmt.Sprintf("invalid port number: %s", value),
        }
    }

    if port < 1 || port > 65535 {
        return 0, &ValidationError{
            Field:   "port",
            Message: "port must be between 1 and 65535",
        }
    }

    return port, nil
}

// ValidateEmail validates an email address
func ValidateEmail(value string) (string, error) {
    pattern := `^[\w.-]+@[\w.-]+\.\w+$`
    matched, _ := regexp.MatchString(pattern, value)

    if !matched {
        return "", &ValidationError{
            Field:   "email",
            Message: "invalid email format",
        }
    }

    return strings.ToLower(value), nil
}

var envAliases = map[string]string{
    "dev":  "development",
    "prod": "production",
}

var validEnvironments = []string{"development", "staging", "production"}

// ValidateEnvironment validates environment name
func ValidateEnvironment(value string) (string, error) {
    if alias, ok := envAliases[value]; ok {
        value = alias
    }

    for _, env := range validEnvironments {
        if env == value {
            return value, nil
        }
    }

    return "", &ValidationError{
        Field:   "environment",
        Message: fmt.Sprintf("invalid environment: %s", value),
    }
}

Validation Patterns

Composite Validators

// URL with specific protocol
export const apiUrlSchema = z
  .string()
  .url()
  .refine(
    (url) => url.startsWith('https://'),
    'API URL must use HTTPS'
  );

// File path that must exist
export const existingFileSchema = z
  .string()
  .refine(
    (path) => fs.existsSync(path),
    (path) => ({ message: `File not found: ${path}` })
  );

Dependent Validation

// Validate that end date is after start date
export const dateRangeSchema = z.object({
  startDate: z.coerce.date(),
  endDate: z.coerce.date(),
}).refine(
  (data) => data.endDate > data.startDate,
  'End date must be after start date'
);

Workflow

1. Analyze requirements - Review validation needs
2. Generate base validators - Type coercion and basic checks
3. Add constraints - Min/max, patterns, enums
4. Create error messages - Helpful, actionable messages
5. Add aliases/transforms - Normalize input values
6. Generate tests - Validation test cases

Best Practices Applied

• Type coercion before validation
• Descriptive error messages
• Input normalization (lowercase, trim)
• Alias support for common values
• Composable validation schemas
• Consistent error types

Target Processes

• argument-parser-setup
• error-handling-user-feedback
• cli-command-structure-design