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Type Narrowing

Checked
marius-townhouse·vlatest·backend

Type Narrowing refines search queries by suggesting more specific types of content, boosting relevance and saving you time finding exactly what you need.

Repository

Install on your platform

Showing Claude Code. One command installs this skill into any of the agents below.

  1. 1

    Run this in your project

    terminal
    $ npx skills add marius-townhouse/effective-typescript-skills --skill type-narrowing -a claude-code

  2. Uses the open-source skills CLI and needs Node.js. Add -g to install it for your user instead of this project.

What we know about this skill

Publisher

marius-townhouse

Taken from the source listing. We haven't verified who controls this account.

Install target

Live repository

Not pinned. Installing fetches whatever the repository holds at the time you run the command.

No human has reviewed this code. The checks below are a static scan of the files at one commit — nobody has run this skill or judged whether it works. A skill runs with whatever access you give your agent, so read the source before you install it.

Automated safety checks

scanned

This skill passed all 6 checks. We read its files at one commit and looked for the things that make a skill dangerous to run — not for whether it works.

  • Declares what it does: passed

    SKILL.md parses and declares a name and a description.

    SKILL.md exists, its frontmatter parses, and it declares a name and a description.

  • No undeclared network calls: passed

    Makes no network calls.

    Every host the skill dials — from its scripts, its config endpoints or the commands it tells the agent to run — is either well-known package and API infrastructure or declared in its own frontmatter. Links in documentation are not counted.

  • No obfuscated payloads: passed

    No encoded or obfuscated payloads.

    No base64, hex or compressed blob is decoded and then executed, and no encoded shell commands.

  • No credential access: passed

    Reads no keys, tokens, keychains or credential files.

    Neither the code nor the SKILL.md instructions read SSH keys, cloud credentials, keychains, token stores, browser cookie databases or dotfiles that hold secrets.

  • No pipe-to-shell installers: passed

    No pipe-to-shell or download-and-run installers.

    No `curl … | sh` pattern, in the code or in the instructions, that runs code fetched at run time.

  • Pinned to a commit: passed

    Scanned marius-townhouse/effective-typescript-skills at d754db2077.

    The exact upstream commit SHA that was scanned is recorded, so the result refers to specific bytes.

Commit
d754db2077
Manifest
skills/type-narrowing/SKILL.md
Scanned
1 file, 273 lines
This is a static scan, not a review. It reads the skill's files; it does not run them, and it cannot tell you whether the skill is any good or whether the code does what its description says. A skill runs with whatever access you give your agent.
What each check looks for →

About this skill

What it does

The type-narrowing skill allows an AI agent to refine the type of a variable within TypeScript code. This process involves using techniques like conditional checks, discriminated unions, and type predicates to ensure that variables are treated as more specific types than initially declared. The goal is to improve code safety and enable more precise operations on data.

When to use it

  • Handling union types: When a variable can be one of several types (a union), this skill helps determine the exact type at runtime for targeted processing.
  • Working with discriminated unions: To safely access properties unique to specific members within a discriminated union.
  • Refining any types: To gradually eliminate any and improve type safety in legacy codebases.
  • Implementing complex conditional logic: When TypeScript's type system needs assistance to correctly infer the type of a variable based on runtime conditions.

Key capabilities

  • Conditional Type Narrowing
  • Discriminated Union Handling
  • Type Predicates
  • Runtime Type Checks

Example prompts

  • "How can I narrow the type of data which is declared as string | number to a number if it's greater than 10?"
  • "I have a discriminated union with a 'kind' property. How do I access properties specific to each kind safely?"
  • “Explain how to use a type predicate in TypeScript.”

Tips & gotchas

This skill requires a basic understanding of TypeScript’s type system and the concepts of unions, intersections, and generics. Incorrect usage can lead to runtime errors if the narrowing logic is flawed.