What problem does it solve? TypeScript developers often face subtle or disputed questions about assignability, inference, narrowing, variance, generics, and conditional types where memory-based answers are unreliable. This Skill grounds those answers in the official TypeScript documentation snapshot and the project's actual pinned compiler, separating documented behavior from empirically observed results. ## Core Features & Use Cases - Topic-indexed reference lookup: A curated index maps each question type (variance, mapped types, ESM/CJS interop, compiler options) to the smallest relevant official documentation files. - Compiler-verified answers: When documentation does not settle an edge case, it guides creating minimal reproductions with positive assignability examples and @ts-expect-error negative cases run against the project's pinned compiler. - Precision guardrails: Distinguishes structural compatibility, excess-property checks, narrowing, inference, and declaration lookup as separate mechanisms, and flags version-sensitive behavior. - Use Case: A teammate claims a callback parameter assignment is safe. Use this Skill to check the variance rules under strictFunctionTypes, reproduce the case with the project's compiler, and report whether the accepted assignability is intentionally unsound. ## Quick Start Ask whether a specific TypeScript generic conditional type distributes over a union and request a verified answer with the project's compiler version.
