Title: PromptBuilder::validateMessages
Published: May 20, 2026

---

# PromptBuilder::validateMessages(): void

## In this article

 * [Description](https://developer.wordpress.org/reference/classes/wordpress-aiclient-builders-promptbuilder/validatemessages/?output_format=md#description)
 * [Return](https://developer.wordpress.org/reference/classes/wordpress-aiclient-builders-promptbuilder/validatemessages/?output_format=md#return)
 * [Source](https://developer.wordpress.org/reference/classes/wordpress-aiclient-builders-promptbuilder/validatemessages/?output_format=md#source)
 * [Related](https://developer.wordpress.org/reference/classes/wordpress-aiclient-builders-promptbuilder/validatemessages/?output_format=md#related)
 * [Changelog](https://developer.wordpress.org/reference/classes/wordpress-aiclient-builders-promptbuilder/validatemessages/?output_format=md#changelog)

[ Back to top](https://developer.wordpress.org/reference/classes/wordpress-aiclient-builders-promptbuilder/validatemessages/?output_format=md#wp--skip-link--target)

This function’s access is marked private. This means it is not intended for use 
by plugin or theme developers, only by core. It is listed here for completeness.

Validates the messages array for prompt generation.

## 󠀁[Description](https://developer.wordpress.org/reference/classes/wordpress-aiclient-builders-promptbuilder/validatemessages/?output_format=md#description)󠁿

Ensures that:

 * The first message is a user message
 * The last message is a user message
 * The last message has parts

## 󠀁[Return](https://developer.wordpress.org/reference/classes/wordpress-aiclient-builders-promptbuilder/validatemessages/?output_format=md#return)󠁿

 void

## 󠀁[Source](https://developer.wordpress.org/reference/classes/wordpress-aiclient-builders-promptbuilder/validatemessages/?output_format=md#source)󠁿

    ```php
    private function validateMessages(): void
    {
        if (empty($this->messages)) {
            throw new InvalidArgumentException('Cannot generate from an empty prompt. Add content using withText() or similar methods.');
        }
        $firstMessage = reset($this->messages);
        if (!$firstMessage->getRole()->isUser()) {
            throw new InvalidArgumentException('The first message must be from a user role, not from ' . $firstMessage->getRole()->value);
        }
        $lastMessage = end($this->messages);
        if (!$lastMessage->getRole()->isUser()) {
            throw new InvalidArgumentException('The last message must be from a user role, not from ' . $lastMessage->getRole()->value);
        }
        if (empty($lastMessage->getParts())) {
            throw new InvalidArgumentException('The last message must have content parts. Add content using withText() or similar methods.');
        }
    }
    ```

[View all references](https://developer.wordpress.org/reference/files/wp-includes/php-ai-client/src/builders/promptbuilder.php/)
[View on Trac](https://core.trac.wordpress.org/browser/tags/7.0/src/wp-includes/php-ai-client/src/Builders/PromptBuilder.php#L1375)
[View on GitHub](https://github.com/WordPress/wordpress-develop/blob/7.0/src/wp-includes/php-ai-client/src/Builders/PromptBuilder.php#L1375-L1391)

## 󠀁[Related](https://developer.wordpress.org/reference/classes/wordpress-aiclient-builders-promptbuilder/validatemessages/?output_format=md#related)󠁿

| Used by | Description | 
| [PromptBuilder::generateResult()](https://developer.wordpress.org/reference/classes/wordpress-aiclient-builders-promptbuilder/generateresult/)`wp-includes/php-ai-client/src/Builders/PromptBuilder.php` |

Generates a result from the prompt.

  |

## 󠀁[Changelog](https://developer.wordpress.org/reference/classes/wordpress-aiclient-builders-promptbuilder/validatemessages/?output_format=md#changelog)󠁿

| Version | Description | 
| [0.1.0](https://developer.wordpress.org/reference/since/0.1.0/) | Introduced. |

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