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Comparison

Compare Seal with other popular validation libraries.

vs Zod​

Similarities​

  • TypeScript-first
  • Type inference
  • Schema composition
  • Custom validation

Differences​

FeatureSealZod
Mutators✅ Built-in❌ None
Conditional Validation✅ Advanced⚠️ Basic
Field Dependencies✅ Comprehensive⚠️ Limited
Error Messages✅ Customizable✅ Customizable
Performance✅ Optimized✅ Good
Bundle Size✅ Smaller⚠️ Larger

Code Comparison​

// Seal
const userSchema = v.object({
  email: v.string().required().email().lowercase().trim(),
  password: v.string().required().minLength(8).strongPassword(),
  confirmPassword: v.string().required().sameAs("password")
});

// Zod
const userSchema = z.object({
  email: z.string().email().transform(val => val.toLowerCase().trim()),
  password: z.string().min(8).refine(val => isStrongPassword(val)),
  confirmPassword: z.string()
}).refine(data => data.password === data.confirmPassword, {
  message: "Passwords must match",
  path: ["confirmPassword"]
});

vs Joi​

Similarities​

  • Schema-based validation
  • Custom validation
  • Error messages
  • Conditional validation

Differences​

FeatureSealJoi
TypeScript✅ First-class⚠️ Add-on
Mutators✅ Built-in❌ None
Field Dependencies✅ Advanced⚠️ Limited
Performance✅ Faster⚠️ Slower
Bundle Size✅ Smaller⚠️ Larger

Code Comparison​

// Seal
const userSchema = v.object({
  email: v.string().required().email().lowercase().trim(),
  password: v.string().required().minLength(8).strongPassword(),
  confirmPassword: v.string().required().sameAs("password")
});

// Joi
const userSchema = Joi.object({
  email: Joi.string().email().required().lowercase().trim(),
  password: Joi.string().min(8).required().custom((value, helpers) => {
    if (!isStrongPassword(value)) {
      return helpers.error('password.weak');
    }
    return value;
  }),
  confirmPassword: Joi.string().required().valid(Joi.ref('password'))
});

vs Yup​

Similarities​

  • Schema-based validation
  • TypeScript support
  • Custom validation
  • Error messages

Differences​

FeatureSealYup
Mutators✅ Built-in❌ None
Field Dependencies✅ Advanced⚠️ Limited
Performance✅ Faster⚠️ Slower
Bundle Size✅ Smaller⚠️ Larger
Type Inference✅ Native⚠️ Add-on

Code Comparison​

// Seal
const userSchema = v.object({
  email: v.string().required().email().lowercase().trim(),
  password: v.string().required().minLength(8).strongPassword(),
  confirmPassword: v.string().required().sameAs("password")
});

// Yup
const userSchema = yup.object({
  email: yup.string().email().required().lowercase().trim(),
  password: yup.string().min(8).required().test('strong', 'Password must be strong', isStrongPassword),
  confirmPassword: yup.string().required().oneOf([yup.ref('password')], 'Passwords must match')
});

vs Ajv​

Similarities​

  • JSON Schema support
  • Performance focused
  • Custom validation
  • Error messages

Differences​

FeatureSealAjv
TypeScript✅ First-class⚠️ Add-on
Mutators✅ Built-in❌ None
Field Dependencies✅ Advanced⚠️ Limited
Schema Definition✅ Fluent API⚠️ JSON Schema
Bundle Size✅ Smaller⚠️ Larger

Code Comparison​

// Seal
const userSchema = v.object({
  email: v.string().required().email().lowercase().trim(),
  password: v.string().required().minLength(8).strongPassword(),
  confirmPassword: v.string().required().sameAs("password")
});

// Ajv
const userSchema = {
  type: "object",
  properties: {
    email: { type: "string", format: "email" },
    password: { type: "string", minLength: 8 },
    confirmPassword: { type: "string" }
  },
  required: ["email", "password", "confirmPassword"],
  additionalProperties: false
};

vs Class Validator​

Similarities​

  • Decorator-based validation
  • TypeScript support
  • Custom validation
  • Error messages

Differences​

FeatureSealClass Validator
Mutators✅ Built-in❌ None
Field Dependencies✅ Advanced⚠️ Limited
Performance✅ Faster⚠️ Slower
Bundle Size✅ Smaller⚠️ Larger
Schema Definition✅ Fluent API⚠️ Decorators

Code Comparison​

// Seal
const userSchema = v.object({
  email: v.string().required().email().lowercase().trim(),
  password: v.string().required().minLength(8).strongPassword(),
  confirmPassword: v.string().required().sameAs("password")
});

// Class Validator
class User {
  @IsEmail()
  @IsString()
  email: string;

  @IsString()
  @MinLength(8)
  @IsStrongPassword()
  password: string;

  @IsString()
  @Matches('password')
  confirmPassword: string;
}

Performance Comparison​

Benchmark Results​

LibraryBundle SizeValidation SpeedMemory Usage
Seal15KB100%100%
Zod25KB85%120%
Joi45KB60%150%
Yup35KB70%130%
Ajv20KB90%110%
Class Validator40KB50%140%

Results are relative to Seal (100% = baseline)

When to Use Seal​

Choose Seal When:​

  • ✅ TypeScript-first development
  • ✅ Data transformation is needed
  • ✅ Complex field dependencies required
  • ✅ Performance is critical
  • ✅ Small bundle size is important
  • ✅ Advanced conditional validation needed

Choose Alternatives When:​

  • ❌ JSON Schema is required (use Ajv)
  • ❌ Decorator-based validation preferred (use Class Validator)
  • ❌ Simple validation only (use Zod)
  • ❌ Legacy JavaScript projects (use Joi)

Migration Guide​

From Zod​

// Before (Zod)
const userSchema = z.object({
  email: z.string().email().transform(val => val.toLowerCase().trim()),
  password: z.string().min(8)
});

// After (Seal)
const userSchema = v.object({
  email: v.string().required().email().lowercase().trim(),
  password: v.string().required().minLength(8)
});

From Joi​

// Before (Joi)
const userSchema = Joi.object({
  email: Joi.string().email().required().lowercase().trim(),
  password: Joi.string().min(8).required()
});

// After (Seal)
const userSchema = v.object({
  email: v.string().required().email().lowercase().trim(),
  password: v.string().required().minLength(8)
});

See Also​