> For the complete documentation index, see [llms.txt](https://docs.forgappify.com/workflow-building-blocks-for-jira/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.forgappify.com/workflow-building-blocks-for-jira/writing-jira-expressions/writing-validation-messages.md).

# 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 %}