# Writing validation messages

{% hint style="info" %}
Validation message expression must evaluate to String
{% endhint %}

Enter text surrounded by quotation marks to provide a static message:

{% code lineNumbers="true" %}

```javascript
"Issue must be assigned!"
```

{% endcode %}

You can add some dynamic content, simply by concatenating strings. Remember to use `?.` notation to prevent syntax errors when a property is null.

{% code lineNumbers="true" %}

```javascript
"Issue can't be assigned, but got: " 
  + issue.assignee?.displayName 
```

{% endcode %}

Use [template literals](https://developer.atlassian.com/cloud/jira/platform/jira-expressions-type-reference/#template-literals) for more complex use cases:

{% code lineNumbers="true" %}

```javascript
`Issue ${issue.key} must have at least 1 comment,
 but got: ${issue.comments.length}!`
```

{% endcode %}