typescript-dev_skill

Overview

This skill focuses on production-grade TypeScript development with strict type safety, modern TS 5.2+ features, and runtime validation using Zod. It provides patterns for eliminating any, building Result types, discriminated unions, branded types, and leveraging new language features like using, satisfies, const type parameters, and inferred predicates. Use it to enforce compile-time guarantees and safe runtime boundaries across APIs, services, and libraries.

How this skill works

The skill inspects code and offers concrete replacements for unsafe patterns (any, non-exhaustive unions, non-validated inputs) and recommends strict tsconfig settings. It suggests Zod schemas and safeParse usage at boundaries, Result-based error handling, branded types for domain safety, and modern TypeScript idioms to preserve literal types and enable automatic cleanup. It also enforces documentation practices via TSDoc for all exports to improve maintainability and AI consumption.

When to use it

• Writing new TypeScript code or migrating existing code toward strict safety
• Eliminating any and replacing it with unknown + guards or validated types
• Validating API inputs/outputs, environment variables, and forms with Zod
• Implementing explicit error handling with Result/Either types
• Modeling finite states with discriminated unions to prevent illegal combinations

Best practices

• Enable strict tsconfig options including noUncheckedIndexedAccess and exactOptionalPropertyTypes
• Prefer unknown + type guards over any; use safeParse instead of parse for Zod
• Use discriminated unions for state, branded types for domain primitives, and Result for errors
• Use satisfies, const type parameters, and inferred predicates (TS 5.5+) to retain literal types and safer generics
• Use using for resource cleanup and add TSDoc for every exported function/type

Example use cases

• Validate HTTP JSON payloads server-side with Zod schemas and safeParse before mapping to domain types
• Replace thrown-only APIs with Result-returning functions and handle errors explicitly in callers
• Model UI request state with discriminated unions to avoid impossible states and simplify rendering logic
• Create branded types (UserId, SanitizedHtml) to prevent accidental mixing of primitives
• Use using for database connections and file handles to guarantee deterministic disposal