About typescript-best-practices
A TypeScript type-system discipline skill for coding agents. It emphasizes validated boundaries, precise modeling, and exhaustiveness checks to reduce unsafe type operations.
Key features
- 01Model variants with discriminated unions
- 02Separate primitives with branded types
- 03Prefer unknown over any
- 04Validate data before assertions
- 05Check exhaustiveness in branches
- 06Derive types from schemas
Use cases
- 01Design validation for external inputs
- 02Model variants without invalid states
- 03Review type guards and assertions
- 04Choose object-shaped function arguments
Install
Copy the command and run it in a terminal.
$
npx skills add https:/After installing, type/typescript-best-practicesin Claude Code to confirm it loaded.
Bundled filesreferences/patterns.md
Details
From the project READMETypeScript best practices
Apply the type-system-discipline principle skill first; this skill grounds it in TypeScript syntax.
| 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 creation. |
unknown over any | External data is unknown. any disables type checking everywhere it touches. |
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 | Validate where data crosses in; 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). |
Examples: references/patterns.md.
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