How to use the TypeScript Type System Expert agent skill

What the skill makes the agent do

When the skill is installed, the agent answers and writes TypeScript with a focus on the type system. The skill's instructions ask it to enable strict compiler settings such as strict, noUncheckedIndexedAccess and exactOptionalPropertyTypes in tsconfig.json, and to prefer code that lets the compiler catch mistakes.

The skill tells the agent to avoid shortcuts. It discourages type assertions with as, treats any as a code smell and suggests unknown with type guards instead. It also favours patterns such as branded types and exhaustive switches. The skill is guidance only: it does not add tools and does not run anything on its own.

• Uses discriminated unions with a literal type field instead of assertions
• Uses Partial, Required, Pick, Omit and Record where they fit
• Suggests branded types for IDs that are both strings but should not be mixed
• Suggests exhaustive switches with an assertNever helper so unhandled union cases fail to compile
• Suggests template literal types for typed route patterns

How to install the typescript-expert skill

Download the ZIP file from this page. The skill ships as a single file, SKILL.md, so the ZIP contains one file inside a folder. Unzip it into your personal skills folder, ~/.claude/skills/, or into a project's .claude/skills/ folder if you want the skill only for that project.

If you use the Claude apps instead, open Settings, go to Capabilities, then Skills, and upload the ZIP there.

• Personal install: unzip into ~/.claude/skills/
• Project install: unzip into the project's .claude/skills/ folder
• Claude apps: Settings → Capabilities → Skills, then upload the ZIP

How to trigger the skill with natural requests

You do not need a special command. The skill is about TypeScript types, generics, utility types and strict mode, so ask for help in those terms. The more specific your request, the more the agent's guidance applies.

Mention the file or code you are working on and what you want the types to do. Ask for a review of type safety if you want the agent to check existing code against these patterns.

• Refactor this function to remove the any and use a generic constraint
• Turn this API response into a discriminated union and add a type guard
• Make this switch exhaustive so the compiler flags missing cases
• Which utility type should I use to make only the email field optional?

Examples of what the agent writes

The skill includes example patterns that the agent can follow. A generic merge function that constrains both inputs to objects looks like this:

• Generic constraints with extends, as in merge<T extends object, U extends object>(a: T, b: U): T & U
• Type guards, such as a function that takes unknown and returns val is string
• A branded UserId type built from string with a unique symbol brand

What you need and safety notes

The source lists no requirements. The skill is a text file of instructions, so it needs an agent that reads skills and a TypeScript project to apply the advice to. It does not run scripts and does not use the network.

Because it does not run anything, the main risk is the advice itself. Strict flags such as exactOptionalPropertyTypes can break many existing files, so review the changes before accepting them.

• Runs scripts: no
• Uses network: no
• Files: SKILL.md only
• Licence: Apache-2.0

Tips and pitfalls to avoid

The skill itself warns against over-engineering. It asks the agent to keep generic types readable rather than clever, so push back if a suggested type is hard to follow.

For an existing codebase, turn on strict flags in a planned migration rather than all at once. Expect the agent to flag the use of enum for string constants; the skill prefers as const objects or union literal types instead.

• Ask for readable types first, then ask for stricter ones
• Migrate strict flags in stages on large codebases
• Remember that Object.keys() is typed as string[] on purpose, so do not expect keyof T back from it