[API reference](https://evolu.dev/docs/api-reference) › [@evolu/common](https://evolu.dev/docs/api-reference/common) › [Leancase](https://evolu.dev/docs/api-reference/common/Leancase) › leancased

```ts
const leancased: BrandFactory<"Leancased", string, LeancasedError>;
```

Defined in: [packages/common/src/Leancase.ts:85](https://github.com/evoluhq/evolu/blob/bc4578a260dd15d5bbf94b83765ca05984d194cb/packages/common/src/Leancase.ts#L85)

**`Experimental`**

Adds leancase validation to an existing string Type.

A string is valid when [leancase](https://evolu.dev/docs/api-reference/common/Leancase/functions/leancase) leaves it unchanged. Validation does
not modify the value.

### Example

```ts
import {
  assertErr,
  assertOk,
  leancased,
  maxLength,
  String,
} from "@evolu/common";

const Post = leancased(maxLength(280)(String));

assertOk(Post.fromUnknown("hello. world"), "hello. world");
assertErr(Post.fromUnknown("Hello. World."));
```