# <small>nlohmann::basic_json::</small>is_boolean

```cpp
constexpr bool is_boolean() const noexcept;
```

This function returns `#!cpp true` if and only if the JSON value is `#!json true` or `#!json false`.
    
## Return value

`#!cpp true` if type is boolean, `#!cpp false` otherwise.

## Exception safety

No-throw guarantee: this member function never throws exceptions.

## Complexity

Constant.

## Examples

??? example

    The following code exemplifies `is_boolean()` for all JSON types.
    
    ```cpp
    --8<-- "examples/is_boolean.cpp"
    ```
    
    Output:
    
    ```json
    --8<-- "examples/is_boolean.output"
    ```

## See also

- [`boolean_t`](boolean_t.md) - the type used to store JSON booleans
- [`is_primitive`](is_primitive.md) - checks whether the JSON value is primitive
- [`basic_json_view::is_boolean`](../basic_json_view/is_boolean.md) - the same check on a zero-copy view
- [Types](../../features/types/index.md) - the JSON value types and how they are stored

## Version history

- Added in version 1.0.0.