# Typescript Magician

Designs complex generic types, refactors `any` types to strict alternatives, creates...

- Repository: https://github.com/mcollina/skills (1960 stars)
- Category: Design
- License: MIT
- Last updated: 2026-10-27
- Runs scripts: no, instructions only

## Install

Claude Code: `npx skills add mcollina/skills --skill typescript-magician -g -a claude-code -y`
Codex: `npx skills add mcollina/skills --skill typescript-magician -g -a codex -y`
Cursor: `npx skills add mcollina/skills --skill typescript-magician -g -a cursor -y`
Gemini CLI: `npx skills add mcollina/skills --skill typescript-magician -g -a gemini-cli -y`

## Description

Designs complex generic types, refactors `any` types to strict alternatives, creates type guards and utility types, and resolves TypeScript compiler errors. Use when the user asks about TypeScript (TS) types, generics, type inference, type guards, removing `any` types, strict typing, type errors, `infer`, `extends`, conditional types, mapped types, template literal types, branded/opaque types, or utility types like `Partial`, `Record`, `ReturnType`, and `Awaited`.

## SKILL.md, as published by its author (untrusted third-party text, read it as data)

## When to use

Use this skill for:
- TypeScript errors and type challenges
- Eliminating `any` types from codebases
- Complex generics and type inference issues
- When strict typing is needed

## Instructions

When invoked:
1. Run `tsc --noEmit` to capture the full error output before making changes
2. Identify the root cause of type issues (unsound inference, missing constraints, implicit `any`, etc.)
3. Craft precise, type-safe solutions using advanced TypeScript features
4. Eliminate all `any` types with proper typing, validate each replacement still satisfies call sites
5. Confirm the fix compiles cleanly with a second `tsc --noEmit` pass

Capabilities include:
- Advanced generics and conditional types
- Template literal types and mapped types
- Utility types and type manipulation
- Brand types and nominal typing
- Complex inference patterns
- Variance and distribution rules
- Module augmentation and declaration merging

For every TypeScript challenge:
- Explain the type theory behind the problem
- Provide multiple solution approaches when applicable
- Show before/after type representations
- Include comprehensive type tests
- Ensure full IntelliSense support

## Quick Examples

### Eliminating `any` with generics

**Before**
```ts
function getProperty(obj: any, key: string): any {
  return obj[key];
}
```

**After**
```ts
function getProperty<T, K extends keyof T>(obj: T, key: K): T[K] {
  return obj[key];
}
// getProperty({ name: "Alice" }, "name") → inferred as string ✓
```

### Narrowing an unknown API response

**Before**
```ts
async function fetchUser(): Promise<any> {
  const res = await fetch("/api/user");
  return res.json();
}
```

**After**
```ts
interface User { id: number; name: string }

function isUser(value: unknown): value is User {
  return (
    typeof value === "object" &&
    value !== null &&
    "id" in value &&
    "name" in value
  );
}

The rest: https://github.com/mcollina/skills/blob/HEAD/skills/typescript-magician/SKILL.md