class-validator

Zod

colinhacks/zod

Popular

TypeScript-first schema validation with static type inference; the most used validator.

Pydantic

pydantic/pydantic

Popular

Rust-cored data validation using Python type hints; the backbone of FastAPI and many AI SDKs.

Ajv

ajv-validator/ajv

Popular

The fastest JSON Schema validator for JavaScript, compiling schemas to optimized code.

Valibot

open-circle/valibot

Rising

Modular, tree-shakable schema library with a tiny bundle footprint; Zod-like DX.

ArkType

arktypeio/arktype

Trending (detected automatically)

Runtime validator using TypeScript-like syntax with very fast, optimized checks.

Standard Schema

standard-schema/standard-schema

New

Common interface implemented by Zod, Valibot and ArkType so libraries accept any validator.

TypeBox

sinclairzx81/typebox

Builds JSON Schema with matching static TypeScript types; native to Fastify.

Joi

hapijs/joi

Legacy

Expressive object schema validation from the hapi ecosystem; superseded by TS-first libraries.

FluentValidation

FluentValidation/FluentValidation

Strongly typed, fluent validation rules for .NET models.