[API reference](https://evolu.dev/docs/api-reference) › [@evolu/common](https://evolu.dev/docs/api-reference/common) › [Type](https://evolu.dev/docs/api-reference/common/Type) › UInt64

```ts
const UInt64:  brand(
  "UInt64",
  BigInt,
  (value) =>
    globalThis.BigInt.asUintN(64, value) === value
      ? ok()
      : err<UInt64Error>({ type: "UInt64", value }),
  (error) =>
    The value ${safelyStringifyUnknownValue(error.value)} is not a valid unsigned 64-bit integer (UInt64).,
) ;
```

Defined in: [packages/common/src/Type.ts:5102](https://github.com/evoluhq/evolu/blob/f0109fb501a593010e858e39248dde1200eeb2d7/packages/common/src/Type.ts#L5102)

Unsigned 64-bit [BigInt](https://evolu.dev/docs/api-reference/common/Type/variables/BigInt).