TypeScript Pro

What it does

When your agent uses it

• Modeling domain IDs with branded types
• Writing conditional or mapped types and custom utility types
• Replacing loose state objects with discriminated unions
• Tightening tsconfig strictness and build speed with project references
• Wiring tRPC for end-to-end type safety

Example prompts

• “Create branded UserId and OrderId types so the two can no longer be mixed up.”
• “Model the fetch state as a discriminated union and add a type guard for the error case.”
• “Write a DeepReadonly utility type and use it on the config object.”
• “Turn on strict mode in tsconfig.json and fix the new errors with tsc --noEmit.”

Requirements

• TypeScript with `tsc`

Workflow steps

5 steps, taken from the first numbered list in SKILL.md.

1. 1Analyze type architecture - Review tsconfig, type coverage, build performance
2. 2Design type-first APIs - Create branded types, generics, utility types
3. 3Implement with type safety - Write type guards, discriminated unions, conditional types; run tsc --noEmit to catch type errors before…
4. 4Optimize build - Configure project references, incremental compilation, tree shaking; re-run tsc --noEmit to confirm zero errors after…
5. 5Test types - Confirm type coverage with a tool like type-coverage; validate that all public APIs have explicit return types; iterate on…

What it can do on your machine

Read from SKILL.md and the folder at commit 1be15d8. It shows what the files ask for, not the result of running them.

• Tool permissions

  Pre-approves nothing: there is no allowed-tools line, so your agent's usual permission prompts apply.

  From allowed-tools in the SKILL.md frontmatter.

• Runs code

  Shell commands in SKILL.md call:

  • tsc

  From the folder's file list and the shell code blocks in SKILL.md.

• Network

  Links to these hosts (documentation or services it may open):

  • github.com
  • synergetic.solutions
  • jeffallan.github.io

  From URLs in SKILL.md, links to its own repository left out.

• Credentials

  Names no API keys, tokens, secrets or passwords.

  From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.

Context cost

TypeScript Pro loads about 1.4k tokens when it runs, and up to ~12k if it reads all its reference files. Until then it costs about 86 tokens; SKILL.md has 320 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it

~86

When it runs · the whole SKILL.md, loaded when a task matches

~1.4k

With references · SKILL.md plus every file in references/, read only if the agent opens them

~12k

Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.

Safety

Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.

SKILL.md

The full file from Jeffallan/claude-skills at commit 1be15d8, republished under its MIT licence (© Jeffallan). 320 words, ~1,405 tokens.

name

typescript-pro

description

Implements advanced TypeScript type systems, creates custom type guards, utility types, and branded types, and configures tRPC for end-to-end type safety. Use when building TypeScript applications requiring advanced generics, conditional or mapped types, discriminated unions, monorepo setup, or full-stack type safety with tRPC.

license

MIT

metadata.author

https://github.com/Jeffallan

metadata.company

https://synergetic.solutions

metadata.version

1.1.0

metadata.domain

language

metadata.triggers

TypeScript, generics, type safety, conditional types, mapped types, tRPC, tsconfig, type guards, discriminated unions

metadata.role

specialist

metadata.scope

implementation

metadata.output-format

code

metadata.related-skills

fullstack-guardian, api-designer

// Branded type for domain modeling
type Brand<T, B extends string> = T & { readonly __brand: B };
type UserId  = Brand<string, "UserId">;
type OrderId = Brand<number, "OrderId">;

const toUserId  = (id: string): UserId  => id as UserId;
const toOrderId = (id: number): OrderId => id as OrderId;

// Usage — prevents accidental id mix-ups at compile time
function getOrder(userId: UserId, orderId: OrderId) { /* ... */ }

type LoadingState = { status: "loading" };
type SuccessState = { status: "success"; data: string[] };
type ErrorState   = { status: "error";   error: Error };
type RequestState = LoadingState | SuccessState | ErrorState;

// Type predicate guard
function isSuccess(state: RequestState): state is SuccessState {
  return state.status === "success";
}

// Exhaustive switch with discriminated union
function renderState(state: RequestState): string {
  switch (state.status) {
    case "loading": return "Loading…";
    case "success": return state.data.join(", ");
    case "error":   return state.error.message;
    default: {
      const _exhaustive: never = state;
      throw new Error(`Unhandled state: ${_exhaustive}`);
    }
  }
}

// Deep readonly — immutable nested objects
type DeepReadonly<T> = {
  readonly [K in keyof T]: T[K] extends object ? DeepReadonly<T[K]> : T[K];
};

// Require exactly one of a set of keys
type RequireExactlyOne<T, Keys extends keyof T = keyof T> =
  Pick<T, Exclude<keyof T, Keys>> &
  { [K in Keys]-?: Required<Pick<T, K>> & Partial<Record<Exclude<Keys, K>, never>> }[Keys];

{
  "compilerOptions": {
    "target": "ES2022",
    "module": "NodeNext",
    "moduleResolution": "NodeNext",
    "strict": true,
    "noUncheckedIndexedAccess": true,
    "noImplicitOverride": true,
    "exactOptionalPropertyTypes": true,
    "isolatedModules": true,
    "declaration": true,
    "declarationMap": true,
    "incremental": true,
    "skipLibCheck": false
  }
}

© Jeffallan, MIT. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file

Files

SKILL.md and 5 other files (references) in skills/typescript-pro of Jeffallan/claude-skills.

• SKILL.md
• references/advanced-types.md
• references/configuration.md
• references/patterns.md
• references/type-guards.md
• references/utility-types.md

Open the folder on GitHubat commit 1be15d8

Used in 1 other repository

We found 1 copy of this SKILL.md (exact, near-identical or edited) in other folders, from 1 other GitHub owner. This page covers the copy in Jeffallan/claude-skills, which our catalogue first saw on October 7, 2026.

• aiskillstore/marketplaceskills/jeffallan/typescript-pro