# XO0437: the string option on a non scalar field

`as "key,string"` writes a scalar field as a JSON string holding its literal (`5` as `"5"`) and reads it back the same way, as Go's `json:",string"` does. Go ignores the option on any other type; Xo refuses it, since a silently ignored option is a wire format bug found in production. Remove the option, or give the field a scalar type. See core 2.2 and decision 0555.

## Example

```xo
struct User {
  tags as "tags,string": List[Int]
} derive Json
```

## Fix

```xo
struct User {
  id as "id,string": Int
} derive Json
```

Run `xo explain XO0437` for this text in a terminal, or see
[section 10.6 of the specification](../../spec/core/#106-diagnostic-codes).