# <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

## Version history

- Added in version 1.0.0.