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<AgentInstructions>

## Submitting Feedback

If you encounter incorrect, outdated, or confusing documentation on this page, submit feedback:

POST https://docs.firebolt.io/feedback

```json
{
  "path": "/reference-sql/functions-reference/json/check-json",
  "feedback": "Description of the issue"
}
```

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</AgentInstructions>

> Reference material for CHECK_JSON function

# CHECK_JSON

Returns `NULL` if the input string is a valid JSON document or `NULL`.
Otherwise, returns an error message.

## Syntax

```sql theme={"theme":{"light":"github-light","dark":"github-dark"}}
CHECK_JSON(<json_string>)
```

## Parameters

| Parameter       | Description                     | Supported input types |
| :-------------- | :------------------------------ | :-------------------- |
| `<json_string>` | The string to validate as JSON. | `TEXT`                |

## Return Type

The `CHECK_JSON` function returns a result of type `TEXT`.

## Remarks

If you don't care about the error message, you can also use the [`JSON_IS_VALID`](/reference-sql/functions-reference/json/json-is-valid) function.

## Examples

**Example**

The following code example validates a simple JSON string:

```sql theme={"theme":{"light":"github-light","dark":"github-dark"}}
SELECT CHECK_JSON('{"name": "John"}');
```

**Returns**: `NULL`

The previous code example returns `NULL` because the input string is valid JSON.

**Example**

The following code example validates a simple JSON string:

```sql theme={"theme":{"light":"github-light","dark":"github-dark"}}
SELECT CHECK_JSON('{"name": "John"}{"name": "John"}');
```

**Returns**: `TAPE_ERROR: The JSON document has an improper structure: missing or superfluous commas, braces, missing keys, etc.`

The previous code example returns an error message because the input string is invalid JSON as it contains two JSON objects next to each other.