About ts-best-practices
A TypeScript policy skill for developers writing or reviewing TypeScript. It sets out rules for safer types, data validation, and exhaustive handling of variants.
Key features
- 01Avoid unsafe type assertions
- 02Prefer unknown to any
- 03Model variants with discriminated unions
- 04Use verified type guards and narrowing
- 05Check exhaustiveness in switches
Use cases
- 01Review TypeScript for unsafe casts
- 02Validate external data at boundaries
- 03Define types for variant-shaped data
Install
Copy the command and run it in a terminal.
$
npx skills add https:/After installing, type/ts-best-practicesin Claude Code to confirm it loaded.
Bundled filesreferences/patterns.md
Details
From the project READMEType Safety
This project's TypeScript policy. Apply when writing or reviewing TypeScript.
| Rule | Summary |
|---|---|
No as casts | Every as is a potential runtime crash. Validate at boundaries, then cast only if earned. Prefer Zod/Valibot over manual validation. |
unknown over any | any disables type checking for everything it touches. External data is always unknown. |
| Discriminated unions | Model variants with a shared literal discriminant. No optional-field bags. |
| Narrowing hierarchy | Prefer: discriminated union switch > in operator > typeof/instanceof > type guard > as |
| Type guards | Must actually verify the claim. Name them isX or hasX. Prefer discriminant narrowing when possible. |
| Exhaustiveness checks | Always add default: never arm to switches over discriminated unions. Use an absurd() helper to reduce boilerplate. |
satisfies over as | When verifying a value matches a type without widening, use satisfies to preserve literal types. |
| Impossible states | If a bug requires asking "can this combination happen?" the type is too loose. Tighten it. |
Read references/patterns.md for code examples of each rule.
Comments
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