Zod is a TypeScript-first schema validation library with static type inference, serving as one of the most widely-adopted validation frameworks in the TypeScript ecosystem. The repository implements a layered architecture: a zero-dependency core (`zod/v4/core`) providing foundational parsing primitives, a minimal tree-shakeable layer (`zod/mini`) for size-constrained environments, and a full-featured classic API (`zod/v4`) with chainable methods, JSON Schema conversion, and backward compatibility with Zod v3. The library supports synchronous and asynchronous parsing, bidirectional codecs (encode/decode), branded types, registries for metadata, and 50+ internationalized error locales. The codebase demonstrates exceptional craftsmanship in its type-level programming, achieving complete type inference from runtime schema definitions back to static TypeScript types. The v4 rewrite introduced a JIT compilation system for parsing (with a `jitless` fallback for CSP-restricted environments), a global singleton pattern for configuration and registries to prevent dual-package hazards in CJS/ESM environments, and a modular package structure enabling sub-path imports with aggressive tree-shaking. The monorepo includes dedicated packages for benchmarking (against Zod v3, Valibot, and ArkType), tree-shaking verification, TypeScript compiler performance testing, module resolution testing, and integration testing with ecosystem libraries like drizzle-zod and the Vercel AI SDK.
Valibot is a modular, type-safe schema validation library for TypeScript with zero external dependencies. It provides a comprehensive set of schemas (string, number, object, array, union, etc.), validation actions (email, minLength, regex, etc.), transformation actions (toNumber, toUpperCase, parseJson, etc.), and composition methods (pipe, fallback, forward, cache). The library is tree-shakeable, supports both sync and async validation, and achieves 100% test coverage. Its architecture follows a consistent action/schema object pattern with a `~run` method for runtime validation and extensive TypeScript generics for type inference (InferInput, InferOutput, InferIssue). The repository is a monorepo containing the core library, a documentation website built with Qwik, a codemod for migrating from Zod to Valibot, a JSON Schema conversion package, and an i18n package for localized error messages. The primary entry point is `library/src/index.ts`, which re-exports all schemas, actions, methods, and utilities. Data flows involve defining schemas, optionally piping actions, and then calling `parse` or `safeParse` to validate input against the schema. The library implements the Standard Schema specification for interoperability.