Agent skill · software engineering · cursor
typescript-best-practices
TypeScript best practices. Use when reading or editing any .ts or .tsx file.
Why this skill is useful
Codifies TypeScript conventions that the AI could infer but now doesn't have to guess.
What it needs
About 2k tokens when loaded. Last updated 2026-08-06. 2,555 stars on the source repository.
What this skill does
TypeScript best practices Apply the type-system-discipline principle skill first. Rule Summary ------ --------- Discriminated unions Model variants with a kind literal discriminant so impossible states can't be represented. No optional-field bags. Branded types Brand primitives with & { readonly brand: "X" } so they can't be mixed up. Validate once at the boundary. Constructive modeling Build the shape so the illegal value can't be constructed. [T, ...T[]] for non-empty, [T, T][] for even length, start plus duration for a range. Not a runtime guard, not a wish for refinement types. Simplest total type Keep T[] while every operation on it stays total. Strengthen to NonEmpty<T> only where the loose type forces !, a cast, or a "should never happen" throw. unknown over any External data is unknown. Schemas before guards Before hand-writing a property-by-property type guard, use the repository's runtime schema library and infer the type from the schema, such as z.infer. No as casts Every as is a runtime crash waiting. Cast only after validation. Narrowing hierarchy Discriminant switch > in operator > typeof/instanceof > user-defined type guard > as. Type guards Must verify the claim. A lying guard is worse than as because the bug hides behind a name that says it's safe. Name them isX or hasX. Exhaustiveness Inline const exhaustive: never = x; in default arms so the compiler errors when a new variant is added. satisfies over as Validates the value without widening literal types. Boundary validation Parse where data crosses in, into a named domain type. Record<string, unknown> (however spelled) stops at that parse. Trust types inside. See the boundary-discipline principle skill. Schema-derived types Reach for Pick/Omit/Parameters/ReturnType/Awaited/typeof before declaring a new interface. Object args Pass objects, not positional, so argument order is self-documenting. Skip on hot paths (per-frame render, tokenizers, parsers). Real tests Don't mock what you can run. …
How to use it
Reference it in AdaL, Claude Code, Cursor or any coding agent — nothing to install:
@skills cursor/typescript-best-practices