# What is tsafe?

Powerful TypeScript features like [assertion functions](https://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-7.html#assertion-functions) or [user-defined type guards](https://www.typescriptlang.org/docs/handbook/advanced-types.html#user-defined-type-guards) are only useful if paired with utility functions.

TypeScript, however, only exports type helpers (e.g. `Record`, `ReturnType`, etc.).

This module provides *«the missing builtins»* such as [the assert function](https://docs.tsafe.dev/assert) and other utilities that cannot be just type helpers.

{% hint style="info" %}
`tsafe` is both an [NPM](https://www.npmjs.com/package/tsafe) and a [Deno](https://deno.land/x/tsafe) module. *(Achieved with* [*denoify*](https://denoify.land)*)*
{% endhint %}