# Typescript Rules

> TypeScript coding conventions Use when this capability is needed.

- Skill: `tomevault-io/typescript-rules-4` (Agent Skill, multi-file: 2 files)
- Install (CLI): `npx skillmds@latest add tomevault-io/typescript-rules-4`
- Raw SKILL.md: https://api.skillmd.com/api/skills/tomevault-io/typescript-rules-4/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: tomevault-io (https://skillmd.com/u/tomevault-io)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/tomevault-io/typescript-rules-4

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# TypeScript Rules

## Types
- Never use `any` — use `unknown` with type guards or explicit types
- Prefer `interface` for object shapes, `type` for unions/intersections
- Export types alongside their functions, not from barrel files
- Use `satisfies` for type-safe object literals: `const x = { ... } satisfies Config`

## Imports
- Use `@/` path alias for imports from `apps/web/src/`
- Group imports: external libs → `@/lib/` → relative slice imports
- Use `type` imports for type-only: `import type { Foo } from './types'`

## Architecture Boundaries

### Vertical slice structure (`src/features/<slice>/`)
- Each slice owns its own server functions, queries, components, and types
- No cross-slice imports — shared code goes in `src/lib/`
- `src/lib/` modules must NOT import from `src/features/`

### File naming
- Server function files: `*.server.ts`
- Query/hooks files: `*.queries.ts`
- Component files: PascalCase (e.g., `SessionCard.tsx`)
- Test files: `*.test.ts(x)` co-located with source

## Error Handling
- Throw typed errors, not strings: `throw new Error('message')`
- Use discriminated unions for result types: `{ ok: true; data: T } | { ok: false; error: string }`
- Catch `unknown`, narrow with `instanceof`

## Functions
- Prefer named function declarations over arrow functions for top-level exports
- Use explicit return types on exported functions
- Keep functions small — max ~50 lines

## Zod
- Validate all external input (API responses, form data, URL params) with Zod
- Co-locate schemas with server functions, not in separate schema files
- Use `z.infer<typeof schema>` for derived types

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> Source: [dlupiak/claude-session-dashboard](https://github.com/dlupiak/claude-session-dashboard) — distributed by [TomeVault](https://tomevault.io).
<!-- tomevault:4.0:skill_md:2026-06-23 -->