Why does my AI use a TypeScript function that doesn't exist?

Because the model remembers APIs from other libraries, older versions, or nowhere at all. It writes a function, method or option that sounds right for the library, and the code looks fine until it's compiled or run.

Why it happens

Cursor's own documentation gives an example: import { debounce } from "react", a function React doesn't export. It's worse with less popular libraries and after version changes, when the model's memory of an API is out of date.

What you can do without Check

Keep TypeScript's errors visible to the agent, and ask it to fix them.
Point the agent at the library's real documentation.

How Check stops it

Check stops a TypeScript write that uses a function, method, export or option a library doesn't have. Your project's own TypeScript (version 5 or 6) decides, against the library's own type definitions, so the answer comes from the library itself, not from a model.

Try it.

100 free blocks, then A$0.10 for each action Check stops, from a prepaid balance. Allowed actions are always free. No subscription. Windows and Linux; macOS isn't supported yet. Get your key at the console, then run this in your own terminal:

npx @golproductions/check@latest --install

Or add Check as a plugin for Claude Code, Gemini CLI, Copilot CLI or Codex: the guide. Everything Check checks, and what it lets through: What Check does.

Your machine checks it before it runs.

100 free blocks. Get your GOL API Key at the console.

Start free Install guide