type▌

This skill guides you through improving type coverage in Python files using Pyrefly, Meta's type checker. Follow this systematic process to add proper type annotations to files.

Layer 1: Language Mechanics

Compile-time state validation through type encoding, eliminating invalid states at the type level. \n \n Covers six core patterns: newtype for type-safe primitives, type state for state machines, PhantomData for variance tracking, marker traits for capability flags, builders for gradual construction, and sealed traits for closed impl sets \n Emphasizes asking \"can the compiler catch this?\" before adding runtime validation, with decision guides mapping common needs to appropriate patterns \n In

End-to-end type-safe APIs for TypeScript with zero code generation. \n \n Shares TypeScript types between client and server automatically—no codegen required, with full type inference across queries, mutations, and subscriptions \n Integrates seamlessly with React Query for caching, optimistic updates, and infinite queries; supports Next.js App Router, Server Components, and WebSocket subscriptions \n Validates all inputs with Zod schemas; includes middleware for authentication, logging, and rat

Static type checking with annotations, generics, protocols, and strict mode enforcement. \n \n Covers type annotations, generics with TypeVars, structural protocols, and type narrowing patterns for catching errors at analysis time \n Includes modern syntax (Python 3.10+ union types), bounded type variables, and generic repository patterns for type-safe APIs \n Provides configuration guidance for mypy strict mode and incremental adoption strategies for existing codebases \n Demonstrates 10 fundam

Use this skill when: