typescript-magician

What the source does

• FilesystemNone observedNo reads or writes in the source
• NetworkNone observedNo outbound calls in the source
• ShellNone observedNo commands run in the source
• DependenciesPinnedNothing floats
• SecretsNone foundNo keys in source

Five audit layers

Gates applied: no behavioural pass.

Audit 0.4.1 · source sha 3f067ed6a979 · 29 Oct 2026Report an issue or request a re-scan

• Publishermcollina GitHub userOwner of the repository this skill is read from
• Source foldermcollina/skills/skills/typescript-magicianThe exact folder we audited
• LicenceMITAs the repository states it
• Commit pinned for this verdict3f067ed6a979A new audit runs when the source changes
• Repository statusNot archivedLast push 1 day ago
• Sandboxed runNot runSkills are read, not executed; layer L4 is skipped

Its 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,…

---
name: typescript-magician
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`.
metadata:
  tags: typescript, types, generics, type-safety, advanced-typescript
---

## 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
  );
}

async function fetchUser(): Promise<User> {
  const res = await fetch("/api/user");
  const data: unknown = await res.json();
  if (!isUser(data)) throw new Error("Invalid user shape");
  return data;
}
```

## Reference

Read individual rule files for detailed explanations and code examples:

### Core Patterns
- [rules/as-const-typeof.md](rules/as-const-typeof.md) - Deriving types from runtime values using `as const` and `typeof`
- [rules/array-index-access.md](rules/array-index-access.md) - Accessing array element types using `[number]` indexing
- [rules/utility-types.md](rules/utility-types.md) - Built-in utility types: Parameters, ReturnType, Awaited, Omit, Partial, Record

### Advanced Generics
- [rules/generics-basics.md](rules/generics-basics.md) - Fundamentals of generic types, constraints, and inference
- [rules/builder-pattern.md](rules/builder-pattern.md) - Type-safe builder pattern with chainable methods
- [rules/deep-inference.md](rules/deep-inference.md) - Achieving deep type inference with F.Narrow and const type parameters

### Type-Level Programming
- [rules/conditional-types.md](rules/conditional-types.md) - Conditional types for type-level if/else logic
- [rules/infer-keyword.md](rules/infer-keyword.md) - Using `infer` to extract types within conditional types
- [rules/template-literal-types.md](rules/template-literal-types.md) - String manipulation at the type level
- [rules/mapped-types.md](rules/mapped-types.md) - Creating new types by transforming existing type properties

### Type Safety Patterns
- [rules/opaque-types.md](rules/opaque-types.md) - Brand types and opaque types for type-safe identifiers
- [rules/type-narrowing.md](rules/type-narrowing.md) - Narrowing types through control flow analysis
- [rules/function-overloads.md](rules/function-overloads.md) - Using function overloads for complex function signatures

### Debugging
- [rules/error-diagnosis.md](rules/error-diagnosis.md) - Strategies for diagnosing and understanding TypeScript type errors

Excerpt, first 4,509 characters of SKILL.md, verbatim from the audited commit. It is text from someone else’s repository, quoted so you can judge it before your agent reads it.

git clone https://github.com/mcollina/skills
git -C skills checkout 3f067ed6a979

Works in

1. 2026-10-29
   ✓SAFE B 89 / 100

   first audit · source 3f067ed6a979

Questions about typescript-magician

• github.com/mcollina/skills/tree/main/skills/typescript-magician — the audited source at commit 3f067ed6a979 and every finding aboveObserved · 29 Oct 2026

Spotted something wrong? Report a correction · Methodology