Typescript Strict

What it does

When your agent uses it

• Fixing TypeScript where type safety matters — type errors
• Tightening compiler strictness

Example prompts

• “TypeScript”
• “type error”
• “strict”
• “/typescript-strict”

Requirements

• Node.js

Workflow steps

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

1. 1Respect the project's tsconfig. Write code that passes the flags it has.
2. 2Fix type errors, don't silence them. No as any, no as unknown as T, no
3. 3Validate at trust boundaries. JSON, network responses, environment, and user
4. 4Prefer narrowing to assertion. A non-null ! or an as cast is acceptable
5. 5Model finite states as discriminated unions, and end exhaustive switches with
6. 6Annotate the return types of exported functions; inference is fine inside.
7. 7Verify with the type checker (the typecheck tool, or the project's own

What it can do on your machine

Read from SKILL.md and the folder at commit 57f6018. 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

  No scripts in the folder and no shell commands in SKILL.md (its code samples are typescript).

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

• Network

  No URLs in SKILL.md.

  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 Strict loads about 1.4k tokens when it runs. Until then it costs about 98 tokens; SKILL.md has 515 words of instructions outside code blocks.

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

~98

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

~1.4k

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 WrongStack/WrongStack at commit 57f6018, republished under its MIT licence (© WrongStack). 515 words, ~1,362 tokens.

name

typescript-strict

description

Use this skill when writing, reviewing, or fixing TypeScript where type safety matters — type errors, narrowing, unsafe casts, or tightening compiler strictness. Triggers: user mentions "TypeScript", "type error", "tsc", "strict", "type safety", "narrowing", "any", "unknown", "discriminated union", "branded type", "noUncheckedIndexedAccess", "exactOptionalPropertyTypes".

version

2.0.0

required-capabilities

filesystem.read, filesystem.write

optional-capabilities

verification.run

// Exhaustive switch — adding a variant becomes a compile error here.
type Block =
  | { type: 'text'; text: string }
  | { type: 'image'; url: string }
  | { type: 'error'; message: string };

function assertNever(value: never): never {
  throw new Error(`Unhandled variant: ${JSON.stringify(value)}`);
}

function render(block: Block): string {
  switch (block.type) {
    case 'text':
      return block.text;
    case 'image':
      return `<img src="${block.url}">`;
    case 'error':
      return block.message;
    default:
      return assertNever(block);
  }
}

// Trust boundary — unknown in, narrowed out.
interface User {
  id: string;
  email: string;
}

function isUser(value: unknown): value is User {
  return (
    typeof value === 'object' &&
    value !== null &&
    typeof (value as Record<string, unknown>).id === 'string' &&
    typeof (value as Record<string, unknown>).email === 'string'
  );
}

const body: unknown = await response.json();
if (!isUser(body)) throw new Error('Unexpected user payload');

// Branded id — a SessionId can no longer be passed where a UserId is expected.
type UserId = string & { readonly __brand: 'UserId' };
const toUserId = (raw: string): UserId => raw as UserId; // the one sanctioned cast

© WrongStack, 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 1 other file in packages/core/skills/typescript-strict of WrongStack/WrongStack.

• SKILL.md
• SKILL.save.md

Open the folder on GitHubat commit 57f6018