# assertStringMatches

Source: https://smartassertions.dev/assertions/assertStringMatches/
Index of every page: https://smartassertions.dev/llms.txt

Assert that a string matches a regular expression, with type narrowing.

A regular expression carries no type-level shape, so this narrows an unknown value to a string and stops there.

## Usage

```ts
import { assertStringMatches } from "@kensio/smartass";

const key: unknown = "2026/08/23/14/orders-1-2026-08-23-14-30-00-000";

assertStringMatches(key, /^\d{4}\/\d{2}\/\d{2}\/\d{2}\//);

// key is now narrowed to a string
```

## Source

Source file: [`src/assert/string-matches/string-matches.assert.ts`](https://github.com/KensioSoftware/smartass/blob/main/src/assert/string-matches/string-matches.assert.ts)