# Unserializable result

Resolve unserializable result errors.

The expression evaluated successfully, but its result cannot be serialized to JSON.

This typically happens when the expression returns an abstract type such as a raw `weekday`, `user`, or `session` object instead of a concrete scalar or collection. Refine the expression to return a serializable type, or convert the value with the appropriate [CQL](/reference/cql/introduction) modifier.

## Response

All error responses follow the [Problem Details (RFC 9457)](/reference/api/overview#errors) format. The `type`, `title`, `status`, and `detail` fields are always present, while `instance` may be omitted depending on the API.

Here is an example of the response returned for this error:

```json
{
  "type": "https://croct.help/api/evaluation/unserializable-result",
  "title": "The result cannot be serialized.",
  "status": 422,
  "detail": "Check if the query can be more specific or try to convert the result to a serializable type."
}
```