Type constraints

Pydantic is a data validation library and parsing framework for Python. It functions as a type-based schema validator that uses standard Python type annotations to ensure input data conforms to predefined structural schemas. The project provides capabilities for parsing raw data into typed objects through automatic type conversion and validation. This includes the serialization of data and the validation of data structures to enforce correctness. The framework covers several application areas, including the verification of API requests and the management of application configurations. It all

ow is a type-safe schema validation library for TypeScript that verifies data integrity at runtime. It functions as a runtime validation framework and type guard utility, ensuring that JavaScript values match expected types and schemas before they are processed. The library synchronizes runtime data checks with static TypeScript type definitions, allowing users to extract type definitions directly from validation predicates. This integration enables type narrowing, where a successful validation result refines the variable type for safer usage in the code. The framework uses a chainable API t

Hotscript is a comprehensive suite of composable utilities designed for performing structural transformations and mathematical operations within the TypeScript type system. It serves as a type-level manipulation library that provides a set of higher-order functions to map, filter, and reduce the structure of type definitions. The project focuses on type-level programming by implementing reusable logic and calculations directly within types. This includes the ability to create custom type functions, implement type-level pattern matching, and compose sequences of transformations where each oper

Zod is a TypeScript-first schema declaration and validation library designed to ensure end-to-end data integrity. It functions as a runtime type guard, allowing developers to define complex data structures through a declarative, chainable syntax. By using these schema definitions, the library automatically derives static TypeScript types, eliminating the need for manual type duplication and ensuring that runtime data matches expected application contracts. The library distinguishes itself through functional schema composition, which enables the creation of hierarchical structures by nesting a

prop-types is a JavaScript object validator and runtime type checker. It serves as a development tool for verifying that object properties match predefined specifications, primarily used to ensure that data passed into React components aligns with expected types. The utility detects data inconsistencies by logging warnings to the console when mismatches occur, rather than throwing exceptions. It employs a stateful warning cache to prevent duplicate logs and restricts validation logic to non-production environments to avoid performance overhead in released builds. The project covers data vali

Meta-typing is a TypeScript metaprogramming toolkit that executes complex algorithms, mathematical operations, and data structure traversals entirely within compile-time type definitions. It functions as a type-level computation engine that evaluates numeric expressions, basic arithmetic, and aggregate calculations through recursive type evaluation and tuple-based data representations during the compilation phase. The library implements a comprehensive collection of advanced algorithms and data structures, including collection manipulation utilities for array slicing, filtering, merging, and

TypeScript is a language that extends standard syntax by adding a static type system. It identifies potential runtime errors by analyzing the behaviors and capabilities of values during the compilation process. The language supports object-oriented structures, including classes with inheritance and member visibility control, as well as flexible function definitions that utilize generics, overloads, and parameter destructuring. The project provides a compiler that manages the build lifecycle through a command-line interface, offering configurable options for module resolution, code generation,

Superstruct is a JavaScript and TypeScript data validation library used to verify that data structures match defined shapes and types. It functions as a composable schema builder and a TypeScript schema validator, ensuring that runtime data checks remain synchronized with static type definitions. The library features a data coercion engine that transforms input values or injects default values before the validation process is executed. It enables the creation of complex validation rules by nesting, merging, or omitting properties from existing structures. Its capabilities cover the validatio

ts-essentials is a comprehensive toolkit of utility types and libraries for TypeScript, providing advanced primitives for recursive structural transformations, runtime assertions, and type guards. It serves as a utility library for performing complex type-level programming to ensure stronger type safety and reduce boilerplate. The project distinguishes itself through a specialized set of tools for deep object manipulation, such as recursively applying read-only or optional modifiers across nested hierarchies. It also provides a dedicated set of strict type constraints to ensure data structure

type-fest is a library of reusable utility types for performing complex transformations and validations on objects, arrays, strings, and numeric ranges in TypeScript. It provides a collection of type definitions designed to handle advanced structural changes and constraints. The project distinguishes itself by offering specialized logic for string literal processing, such as casing transformations and pattern-based modifications, and type-level arithmetic for calculating numeric ranges and absolute values. It also includes utilities for enforcing deep immutability, ensuring union mutual exclu

Valibot is a modular, type-safe schema library for validating and parsing structural data in TypeScript environments.

ts-toolbelt is a collection of specialized utilities for manipulating and validating TypeScript types. It provides a toolkit for performing complex transformations on objects, unions, and functions to enforce strict data consistency at compile time. The library features dedicated transformers for function types, including utilities for currying, composition, and signature extraction. It also includes an object type manipulator for deep merging, patching, and reshaping complex structures. The capability surface extends to literal string processing, type-level arithmetic, and tuple operations.

io-ts is a TypeScript runtime validation library that provides a composable codec system for decoding and encoding data at the boundaries of an application. It defines data schemas using structural types, where the shape of data determines its validity rather than nominal names, and produces runtime type guards from those definitions for efficient validation checks. The library is built around bidirectional codec mappings that combine decoding, encoding, and type checking into single reusable units. It supports a composable decoder pipeline where small validation steps can be chained together

Arktype is a TypeScript runtime validation library and schema orchestrator. It synchronizes TypeScript types with runtime data validation, allowing users to define type-safe schemas that ensure unknown data adheres to specific structures during application execution. The project distinguishes itself by using set-theory type analysis to determine intersections and subtype compatibility, alongside JIT-compiled validation functions for optimized performance. It supports advanced type modeling through branded type constraints, recursive alias resolution, and the ability to generate runtime valida

fp-ts is a TypeScript library that brings pure functional programming patterns to the language through algebraic data types, type class abstractions, and composable combinators. It provides foundational data types like Option for optional values, Either for typed error handling, and Task for lazy asynchronous computations, all designed to make invalid states unrepresentable and side effects explicit. The library is built on category theory concepts, offering type classes such as Functor, Applicative, Monad, Semigroup, and Monoid with lawful instances for common data structures. The library di

This library is a collection of zero-overhead C++ abstractions designed to replace primitive types with strict wrappers. By leveraging template metaprogramming, it enforces compile-time type safety and validates data integrity, ensuring that logic errors are caught during the build process rather than at runtime. The project distinguishes itself by providing a zero-cost abstraction layer that maps high-level type safety wrappers directly to machine instructions. It utilizes static type identity enforcement to treat logically distinct data as incompatible types, even when they share the same u

Pydantic is a data validation and serialization library that enforces schema constraints and performs type conversion on complex data structures. It utilizes standard Python type annotations to define data models, allowing developers to establish structured schemas that automatically enforce business rules and constraints without the need for custom domain-specific languages. The library distinguishes itself by transforming high-level model definitions into optimized code during initialization to minimize runtime overhead. It supports recursive validation for nested data structures and employ

Pytype is a static code analysis tool and type inference engine for Python. It functions as a static type analyzer that detects type mismatches and verifies type annotations without requiring full manual hinting, while also serving as a type stub generator for producing standalone definition files. The project distinguishes itself by automatically determining variable and function types through an analysis of code patterns and assignments. This inference engine allows for structural code verification and the generation of type stubs that describe the interfaces of modules and functions. The

Flow is a JavaScript static type checker and AST parser that identifies type errors and prevents runtime failures through static annotations. It functions as a code intelligence engine and a static analysis linter to identify unsafe coding patterns and enforce consistency across a codebase. The project includes a type annotation stripper that removes static type signatures from source code, ensuring the resulting JavaScript is compatible with any runtime environment. It also provides a parser that converts typed JavaScript into an abstract syntax tree conforming to the ESTree specification.

This library provides a type system for Ruby applications, offering a framework for defining, validating, and coercing data structures. It serves as a foundation for maintaining data integrity by ensuring that input values conform to established schemas and constraints before they are processed by application logic. The system distinguishes itself through a functional approach to data transformation and validation. It utilizes an immutable registry for type definitions and employs algebraic operators to compose complex, nested schemas from smaller, reusable components. By wrapping validation

This is a TypeScript utility type library providing advanced type aliases and mapped types for complex object and union transformations. It implements specialized tools for creating branded nominal types, extracting type metadata, and performing set operations on union types. The project distinguishes itself through a toolkit for recursive object transformations, allowing for the application of property constraints like read-only or optional status across deeply nested structures. It also provides a system for computing intersections, differences, and complements between union types to simula

Python static typing home. Hosts the documentation and a user help forum.

Phantom types for Python.

This project is a static analysis engine and type checker designed for PHP codebases. It evaluates source code structure and type annotations to identify potential bugs, type mismatches, and logic errors without executing the application. By parsing code into an abstract syntax tree and applying a rule-based validation framework, it enforces code quality and safety standards across a project. What distinguishes this tool is its sophisticated type inference engine, which models dynamic language features, magic methods, and conditional types to maintain accuracy even in unconventional code. It

An optional type system for Clojure