Open-source alternatives to Mypy

Typeshed is a collection of static type definitions and stubs for the Python standard library and third-party packages. It serves as a standardized resource for static analyzers and integrated development environments to validate code correctness and provide type-based code completion without modifying the original source code of the libraries. The project focuses on the creation and maintenance of external type hint files that separate type annotations from runtime implementation. It utilizes a system for versioning and mapping these stubs to specific versions of runtime packages to maintain

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

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

This project is a comprehensive educational resource and programming course covering C++ language semantics and features from C++03 through C++26. It provides structured tutorials and technical guides focused on modern C++ development. The material offers specialized instruction on template metaprogramming, including the use of type traits and compile-time computations. It features detailed guides on concurrency and parallelism for multi-core execution, as well as a reference for software design applying SOLID principles and RAII. Additionally, it covers build performance optimization to redu

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

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.

Stylelint is a static code analysis tool and linter for CSS and style-like languages. It identifies errors, enforces coding conventions, and operates as a PostCSS plugin to validate stylesheets during build pipelines. The project distinguishes itself through support for non-standard syntaxes, including preprocessor parsing for SCSS and Less, and the ability to extract and lint embedded styles from JavaScript, HTML, and template literals. It features an automated fixing system that programmatically corrects repairable styling violations to ensure consistency. The system provides a plugin arch

Checkstyle is a Java static analysis tool and linter designed to identify and enforce coding standards and best practices. It functions as a code quality auditor and Javadoc validation tool, checking source code against configurable rulesets to ensure structural and stylistic consistency. The project allows for the creation of custom linting rules by extending a core API to inspect the abstract syntax tree. It further enables specialized validation through the use of XPath expressions to query the syntax tree for specific code patterns and violations. Capability areas include the enforcement

Dependency-cruiser is a JavaScript and TypeScript dependency analyzer and architectural linter. It serves as a static analysis tool for mapping, visualizing, and validating module relationships within a codebase without requiring code execution. The project is distinguished by its ability to enforce architectural boundaries through a rule-based system. It detects circular dependencies, identifies orphan modules and dead code, and validates dependency constraints using allowed and forbidden relationship rules. It also provides quantitative stability analysis by calculating afferent and efferen

MonkeyType is a runtime type inferencer and analysis tool for Python. It collects actual argument and return types from function calls during program execution to automate the production of static type annotations and compatible stub files. The system converts captured execution traces into static type hints, which can be inserted directly into source code function definitions or used to generate external type stubs. This process allows for the addition of type safety to existing codebases by analyzing real-world data types rather than through manual auditing. The tool's capabilities cover r

pytest is a testing framework for Python that provides a command-line runner for discovering and executing test suites. It is built on a modular architecture that uses standard language assertions to verify code correctness, automatically inspecting expressions to provide detailed failure reports without requiring specialized assertion methods. The framework distinguishes itself through a dependency injection system that manages setup and teardown logic by automatically resolving and injecting resources into test functions. It also features a hook-based plugin architecture that allows for dee

This project is an uncompromising, deterministic code formatter for Python. It functions by parsing source code into an abstract syntax tree and regenerating it according to a rigid, opinionated set of style rules. By automating the formatting process, it eliminates manual style debates and configuration overhead, ensuring that code remains consistent across entire projects regardless of the original input. The tool distinguishes itself through its focus on speed and seamless integration into development workflows. It utilizes content-based file caching and parallel processing to maintain hig

This tool is a command-line utility designed to automatically detect and correct coding standard violations in PHP source files. It functions as a static analysis and refactoring engine that ensures consistent project-wide formatting by applying predefined community conventions or custom organizational rules. The project distinguishes itself through a modular rule-based engine that supports both automated style correction and codebase modernization. It allows developers to update legacy syntax to align with newer language versions and testing framework requirements, facilitating the adoption

This project is a comprehensive guide and educational resource for the TypeScript language. It covers the fundamental principles of the language, including its structural type system, static type analysis, and the process of transpiling typed source files into JavaScript. The material details how to model complex data and reusable type logic using generics, conditional types, and mapped types. It also explains the use of declaration files to provide type safety for external JavaScript libraries and the integration of type checking into existing JavaScript projects via JSDoc annotations. The

Detekt is a static analysis tool, code quality linter, and complexity analyzer for Kotlin source code. It functions as a code smell detector and static scanner designed to identify potential bugs, design flaws, and violations of coding standards without executing the program. The tool differentiates itself through the use of issue baselining, which allows users to create a snapshot of existing legacy code issues to filter out old violations and focus on preventing new regressions. It further supports extensibility via a plugin-based system that allows for the integration of custom rule sets a

Luau is a high-performance programming language evolved from Lua 5.1. It consists of a bytecode virtual machine, an embeddable scripting engine, and a static code analyzer designed to provide a secure, sandboxed execution environment for host applications. The project is distinguished by its gradual typing system, which combines automatic type inference with optional manual annotations to detect bugs without requiring full static typing. It also features native vector mathematics for high-performance operations and a specialized debugging system that uses bytecode patching to minimize executi

The Concise TypeScript Book: A Concise Guide to Effective Development in TypeScript. Free and Open Source.

Monty is a sandboxed execution environment designed primarily for running Python code generated by AI models. It provides a secure, isolated runtime that blocks host access, enforces resource limits, and supports pre-execution type checking against built-in type hints to catch signature mismatches before code runs. The sandbox can persist its interpreter state at external function calls, allowing execution sessions to be serialized, stored, and later resumed from a file or database. What distinguishes Monty is its combination of stateful, resumable execution with multi-language native embeddi

SwiftLint is a static analysis tool and code formatter designed to enforce consistent coding styles and identify semantic issues within Swift source code. It functions as a command-line utility that evaluates code against established conventions to ensure uniform structure and architectural standards across a project. The tool distinguishes itself through a custom linting engine that leverages compiler-integrated syntax analysis to perform deep inspections of code structure. Beyond simple pattern matching, it supports automated source code transformation to correct formatting violations and r

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

This project is a comprehensive, curated directory of static analysis, linting, and security scanning utilities. It serves as a central resource for developers to discover, compare, and select tools based on specific programming languages, licensing models, and integration requirements. The directory distinguishes itself by providing deep metadata for each listed utility, including community-driven popularity rankings, maintenance status, and deployment methods. By aggregating these tools into a single searchable index, it enables teams to identify solutions for enforcing coding standards, ma

This project is a comprehensive collection of reference materials, including a language cheatsheet, a standard library reference, and a concurrency reference. It serves as a guide to modern C++ development, focusing on language syntax, standard library utilities, and template metaprogramming patterns. The repository provides specific guidance on template metaprogramming through a dedicated guide covering compile-time evaluation, type deduction, and variadic template execution. The materials cover a broad range of capabilities, including asynchronous programming, memory management, and system

Standard is a suite of static analysis tools for JavaScript, comprising a linter, formatter, and a predefined style guide. It functions as a static code analyzer that scans source code for style violations and potential errors without executing the program. The project provides an automatic code fixer that rewrites source code to resolve formatting issues and enforce syntax consistency. It implements a standardized set of rules for JavaScript formatting and syntax to ensure a uniform appearance across different projects. The system covers a wide range of static analysis capabilities, includi

p3c is a Java static analysis tool and code quality linter designed to enforce professional coding guidelines and quality standards. It utilizes a set of custom rules based on the PMD engine to scan source code for style violations, performance bottlenecks, and potential bugs. The project is distributed as an IDE linting plugin that provides real-time feedback and warnings during development. It also includes functionality for pre-commit code quality gates, allowing modified files to be scanned and blocked if they violate defined rules before being committed to version control. The analysis

This library provides a declarative approach to conditional logic in TypeScript, replacing imperative branching with structural pattern matching. It functions as a tool for decomposing complex data structures and mapping them to specific execution branches, ensuring that all possible states are accounted for during development. The library distinguishes itself by enforcing exhaustive logic, which requires developers to address every possible branch of a data structure to prevent runtime errors. By leveraging compile-time type narrowing and recursive evaluation, it allows for the validation an

Biome is a unified developer tooling suite that provides code formatting, linting, and static analysis for JavaScript and TypeScript projects. It functions as a command-line interface designed to automate the maintenance of code quality and style consistency throughout the development lifecycle. The tool distinguishes itself through a high-performance engine built in Rust, which utilizes a single-pass abstract syntax tree to perform formatting and linting simultaneously. By leveraging parallel multi-threaded execution and incremental file system caching, it minimizes latency during analysis t

Prettier is an opinionated code formatter that parses source code and reprints it from scratch to enforce a consistent, project-wide visual style. By transforming code into an abstract syntax tree and applying a recursive document printing process, it eliminates manual style debates and ensures that all source files adhere to a unified appearance. The project is distinguished by its extensible, plugin-based architecture, which decouples language-specific parsing logic from the core engine. This modular design allows for uniform style enforcement across diverse programming languages and comple