Type annotation systems

mypy is a static type checker for Python that analyzes source code to detect type errors and inconsistencies without executing the program. It functions as a static analysis tool and type inference engine, providing a gradual typing system that allows type hints to be added to a codebase incrementally while maintaining compatibility with dynamic typing. The project distinguishes itself through a combination of performance and precision features. It utilizes a daemon-based incremental checking system and multi-process parallel analysis to manage large codebases, supported by binary cache persi

This project is a high-performance static type checker and comprehensive development toolkit for Python. It functions as a core analysis engine that identifies type inconsistencies and enforces code correctness, while simultaneously providing a language server implementation to deliver real-time diagnostics and intelligence directly within development environments. The tool distinguishes itself through a parallelized execution engine that maximizes performance across large-scale codebases and monorepo structures. It supports gradual type adoption, allowing developers to integrate type checkin

Pyrefly is a static type checker for Python that operates as a language server, delivering real-time diagnostics, completions, and navigation in any editor supporting the Language Server Protocol. It also performs static tensor shape analysis, using symbolic dimension variables and arithmetic to verify shape consistency in deep learning models without runtime execution. Beyond core type checking, Pyrefly supports gradual adoption workflows: it can generate a baseline of known errors so only new issues are reported, migrate configuration from other type checkers, and automatically suppress exi

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.

Pyright is a static type checker for Python designed to validate type hints and identify potential errors within large codebases. It functions as a command-line utility that integrates into local development environments and continuous integration pipelines to ensure code quality and consistency. The tool distinguishes itself through a high-performance analysis engine that utilizes incremental dependency graph analysis and persistent state caching to re-evaluate only the affected portions of a project. By implementing the Language Server Protocol, it provides real-time feedback, including err

Phan is a static analyzer and type checker for PHP that identifies bugs and type incompatibilities without executing the code. It serves as a quality gate for continuous integration pipelines and a tool for verifying type safety, specifically checking union types, generics, and array shapes. The project is distinguished by its use of a background daemon and Language Server Protocol implementation, which provide real-time diagnostics and navigation within editors. It also features a baseline-based suppression system that allows developers to record existing errors in a snapshot file to focus e

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,

This project is a suite of specialized tools for the implementation of a language server, template parsing, and static type validation of single-file components. It provides a language server and a type checker to deliver consistent intelligence and validation for Vue components across different editors and command-line environments. The tooling utilizes a template parser to transform single-file component structures into virtual code, enabling static analysis and type checking on HTML-like structures. This process allows for the extraction of component metadata regarding props, events, and s

Sorbet is a static analysis tool and type checker designed for Ruby codebases. It identifies type inconsistencies, potential bugs, and logic errors by examining source code without execution, helping to improve software reliability and maintainability in large-scale projects. The system employs a constraint-based type inference engine that evaluates expressions against defined annotations to validate data structures. To support rapid development, it utilizes incremental analysis and caching to provide feedback by processing only modified files and their dependencies. Beyond static analysis,

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

Pyre is a high-performance static type checker and analysis tool for Python. It identifies type errors and ensures type safety without executing the program, utilizing a static type inference engine to maintain consistency across functions. The project is distinguished by an incremental type analysis engine that operates as a background daemon. This system monitors filesystem changes to re-validate only modified parts of a project, reducing the time required for repeated analysis. It also includes a static analysis security tool that uses taint analysis to track untrusted data flows and ident

ReScript is a statically typed programming language and compiler designed to transform type-safe source code into efficient, human-readable JavaScript. It functions as a transpiler that enforces data consistency and prevents runtime errors through static type analysis for both web and server applications. The project distinguishes itself as an incremental build system that analyzes dependency graphs to recompile only modified files and their dependents. It includes a JSX compatible compiler for building user interfaces and provides a framework for bridging type-safe code with existing JavaScr

lua-language-server is a static analysis tool and type checker for the Lua language that implements the Language Server Protocol. It provides a system for detecting type mismatches, unused code, and logic errors in source files. The project features an inference-based type system that deduces variable types and supports optional annotations and meta files to enforce type safety. It allows for the definition of custom types and function signatures, including support for overloads and member visibility controls. The server provides a broad set of IDE capabilities, including real-time code auto

This project is a JavaScript optimizer, minifier, module bundler, transpiler, and static analysis tool. It provides a compilation pipeline designed to shrink file sizes and improve runtime performance. The system utilizes a multi-pass compilation process to perform dead code elimination, global name mangling, and static type inference. It identifies unreachable functions and unused variables to reduce the final output size and detects potential runtime errors without executing the code. The tool manages assets through dependency resolution, code chunking, and bundle management. It ensures co

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

A CLI tool to automatically add type annotations into Python code.