[AI Bundle][Agent] Add support for prompt as file

demo/config/packages/ai.yaml

@@ -13,11 +13,8 @@ ai:
                   method: 'now'
         stream:
             model: 'gpt-4o-mini'
-            prompt: |
-                You are an example chat application where messages from the LLM are streamed to the user using
-                Server-Sent Events via `symfony/ux-turbo` / Turbo Streams. This example does not use any custom
-                javascript and solely relies on the built-in `live` & `turbo_stream` Stimulus controllers.
-                Whatever the user asks, tell them about the application & used technologies.
+            prompt:
+                file: '%kernel.project_dir%/prompts/stream-chat.txt'
             tools: false
         youtube:
             model: 'gpt-4o-mini'

demo/prompts/stream-chat.txt

@@ -0,0 +1,4 @@
+You are an example chat application where messages from the LLM are streamed to the user using
+Server-Sent Events via `symfony/ux-turbo` / Turbo Streams. This example does not use any custom
+javascript and solely relies on the built-in `live` & `turbo_stream` Stimulus controllers.
+Whatever the user asks, tell them about the application & used technologies.

examples/misc/prompt-json-file.php

@@ -0,0 +1,31 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+use Symfony\AI\Agent\Agent;
+use Symfony\AI\Agent\InputProcessor\SystemPromptInputProcessor;
+use Symfony\AI\Platform\Bridge\OpenAi\PlatformFactory;
+use Symfony\AI\Platform\Message\Content\File;
+use Symfony\AI\Platform\Message\Message;
+use Symfony\AI\Platform\Message\MessageBag;
+
+require_once dirname(__DIR__).'/bootstrap.php';
+
+$platform = PlatformFactory::create($_ENV['OPENAI_API_KEY'], http_client());
+
+// Load system prompt from a JSON file
+$promptFile = File::fromFile(dirname(__DIR__, 2).'/fixtures/prompts/code-reviewer.json');
+$systemPromptProcessor = new SystemPromptInputProcessor($promptFile);
+
+$agent = new Agent($platform, 'gpt-4o-mini', [$systemPromptProcessor], logger: logger());
+$messages = new MessageBag(Message::ofUser('Review this code: function add($a, $b) { return $a + $b; }'));
+$result = $agent->call($messages);
+
+echo $result->getContent().\PHP_EOL;

examples/misc/prompt-text-file.php

@@ -0,0 +1,31 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+use Symfony\AI\Agent\Agent;
+use Symfony\AI\Agent\InputProcessor\SystemPromptInputProcessor;
+use Symfony\AI\Platform\Bridge\OpenAi\PlatformFactory;
+use Symfony\AI\Platform\Message\Content\File;
+use Symfony\AI\Platform\Message\Message;
+use Symfony\AI\Platform\Message\MessageBag;
+
+require_once dirname(__DIR__).'/bootstrap.php';
+
+$platform = PlatformFactory::create($_ENV['OPENAI_API_KEY'], http_client());
+
+// Load system prompt from a plain text file (.txt)
+$promptFile = File::fromFile(dirname(__DIR__, 2).'/fixtures/prompts/helpful-assistant.txt');
+$systemPromptProcessor = new SystemPromptInputProcessor($promptFile);
+
+$agent = new Agent($platform, 'gpt-4o-mini', [$systemPromptProcessor], logger: logger());
+$messages = new MessageBag(Message::ofUser('Can you explain what dependency injection is?'));
+$result = $agent->call($messages);
+
+echo $result->getContent().\PHP_EOL;

fixtures/prompts/code-reviewer.json

@@ -0,0 +1,12 @@
+{
+  "role": "You are an expert code reviewer with deep knowledge of software engineering best practices, design patterns, and code quality.",
+  "responsibilities": [
+    "Review code for bugs and potential issues",
+    "Suggest improvements for code quality and maintainability",
+    "Identify security vulnerabilities",
+    "Recommend better design patterns when appropriate",
+    "Ensure code follows language-specific best practices"
+  ],
+  "tone": "constructive and educational",
+  "approach": "Provide thorough but concise feedback with specific suggestions and examples when helpful"
+}

fixtures/prompts/helpful-assistant.txt

@@ -0,0 +1,8 @@
+You are a helpful and knowledgeable assistant. Your goal is to provide accurate, concise, and useful responses to user queries.
+
+Guidelines:
+- Be clear and direct in your responses
+- Provide examples when appropriate
+- If you're unsure about something, say so
+- Be respectful and professional at all times
+- Break down complex topics into understandable explanations

src/agent/src/InputProcessor/SystemPromptInputProcessor.php

@@ -17,6 +17,7 @@
 use Symfony\AI\Agent\Input;
 use Symfony\AI\Agent\InputProcessorInterface;
 use Symfony\AI\Agent\Toolbox\ToolboxInterface;
+use Symfony\AI\Platform\Message\Content\File;
 use Symfony\AI\Platform\Message\Message;
 use Symfony\AI\Platform\Tool\Tool;
 use Symfony\Contracts\Translation\TranslatableInterface;
@@ -28,11 +29,11 @@
 final readonly class SystemPromptInputProcessor implements InputProcessorInterface
 {
     /**
-     * @param \Stringable|TranslatableInterface|string $systemPrompt the system prompt to prepend to the input messages
-     * @param ToolboxInterface|null                    $toolbox      the tool box to be used to append the tool definitions to the system prompt
+     * @param \Stringable|TranslatableInterface|string|File $systemPrompt the system prompt to prepend to the input messages, or a File object to read from
+     * @param ToolboxInterface|null                         $toolbox      the tool box to be used to append the tool definitions to the system prompt
      */
     public function __construct(
-        private \Stringable|TranslatableInterface|string $systemPrompt,
+        private \Stringable|TranslatableInterface|string|File $systemPrompt,
         private ?ToolboxInterface $toolbox = null,
         private ?TranslatorInterface $translator = null,
         private LoggerInterface $logger = new NullLogger(),
@@ -52,9 +53,13 @@ public function processInput(Input $input): void
             return;
         }
 
-        $message = $this->systemPrompt instanceof TranslatableInterface
-            ? $this->systemPrompt->trans($this->translator)
-            : (string) $this->systemPrompt;
+        if ($this->systemPrompt instanceof File) {
+            $message = $this->systemPrompt->asBinary();
+        } elseif ($this->systemPrompt instanceof TranslatableInterface) {
+            $message = $this->systemPrompt->trans($this->translator);
+        } else {
+            $message = (string) $this->systemPrompt;
+        }
 
         if ($this->toolbox instanceof ToolboxInterface
             && [] !== $this->toolbox->getTools()

src/agent/tests/InputProcessor/SystemPromptInputProcessorTest.php

@@ -18,6 +18,7 @@
 use Symfony\AI\Fixtures\Tool\ToolNoParams;
 use Symfony\AI\Fixtures\Tool\ToolRequiredParams;
 use Symfony\AI\Platform\Bridge\OpenAi\Gpt;
+use Symfony\AI\Platform\Message\Content\File;
 use Symfony\AI\Platform\Message\Message;
 use Symfony\AI\Platform\Message\MessageBag;
 use Symfony\AI\Platform\Message\SystemMessage;
@@ -221,6 +222,49 @@ public function testWithMissingTranslator()
         );
     }
 
+    public function testProcessInputWithFile()
+    {
+        $tempFile = tempnam(sys_get_temp_dir(), 'prompt_');
+        file_put_contents($tempFile, 'This is a system prompt from a file');
+
+        try {
+            $file = File::fromFile($tempFile);
+            $processor = new SystemPromptInputProcessor($file);
+
+            $input = new Input(new Gpt('gpt-4o'), new MessageBag(Message::ofUser('This is a user message')));
+            $processor->processInput($input);
+
+            $messages = $input->messages->getMessages();
+            $this->assertCount(2, $messages);
+            $this->assertInstanceOf(SystemMessage::class, $messages[0]);
+            $this->assertInstanceOf(UserMessage::class, $messages[1]);
+            $this->assertSame('This is a system prompt from a file', $messages[0]->content);
+        } finally {
+            unlink($tempFile);
+        }
+    }
+
+    public function testProcessInputWithMultilineFile()
+    {
+        $tempFile = tempnam(sys_get_temp_dir(), 'prompt_');
+        file_put_contents($tempFile, "Line 1\nLine 2\nLine 3");
+
+        try {
+            $file = File::fromFile($tempFile);
+            $processor = new SystemPromptInputProcessor($file);
+
+            $input = new Input(new Gpt('gpt-4o'), new MessageBag(Message::ofUser('This is a user message')));
+            $processor->processInput($input);
+
+            $messages = $input->messages->getMessages();
+            $this->assertCount(2, $messages);
+            $this->assertInstanceOf(SystemMessage::class, $messages[0]);
+            $this->assertSame("Line 1\nLine 2\nLine 3", $messages[0]->content);
+        } finally {
+            unlink($tempFile);
+        }
+    }
+
     private function getTranslator(): TranslatorInterface
     {
         return new class implements TranslatorInterface {

src/ai-bundle/config/options.php

@@ -306,22 +306,35 @@
                                     return ['text' => $v];
                                 })
                             ->end()
-                            ->beforeNormalization()
-                                ->ifArray()
-                                ->then(function (array $v) {
-                                    if (!isset($v['text']) && !isset($v['include_tools'])) {
-                                        throw new \InvalidArgumentException('Either "text" or "include_tools" must be configured for prompt.');
+                            ->validate()
+                                ->ifTrue(function ($v) {
+                                    if (!\is_array($v)) {
+                                        return false;
                                     }
+                                    $hasTextOrFile = isset($v['text']) || isset($v['file']);
 
-                                    return $v;
+                                    return !$hasTextOrFile;
+                                })
+                                ->thenInvalid('Either "text" or "file" must be configured for prompt.')
+                            ->end()
+                            ->validate()
+                                ->ifTrue(function ($v) {
+                                    return \is_array($v) && isset($v['text']) && isset($v['file']);
                                 })
+                                ->thenInvalid('Cannot use both "text" and "file" for prompt. Choose one.')
                             ->end()
                             ->validate()
                                 ->ifTrue(function ($v) {
-                                    return \is_array($v) && '' === trim($v['text'] ?? '');
+                                    return \is_array($v) && isset($v['text']) && '' === trim($v['text']);
                                 })
                                 ->thenInvalid('The "text" cannot be empty.')
                             ->end()
+                            ->validate()
+                                ->ifTrue(function ($v) {
+                                    return \is_array($v) && isset($v['file']) && '' === trim($v['file']);
+                                })
+                                ->thenInvalid('The "file" cannot be empty.')
+                            ->end()
                             ->validate()
                                 ->ifTrue(function ($v) {
                                     return \is_array($v) && ($v['enabled'] ?? false) && !interface_exists(TranslatorInterface::class);
@@ -332,6 +345,9 @@
                                 ->stringNode('text')
                                     ->info('The system prompt text')
                                 ->end()
+                                ->stringNode('file')
+                                    ->info('Path to file containing the system prompt')
+                                ->end()
                                 ->booleanNode('include_tools')
                                     ->info('Include tool definitions at the end of the system prompt')
                                     ->defaultFalse()

src/ai-bundle/doc/index.rst

@@ -275,11 +275,62 @@ For more control, such as including tool definitions in the system prompt, use t
 
 The array format supports these options:
 
-* ``text`` (string, required): The system prompt text that will be sent to the AI model
+* ``text`` (string): The system prompt text that will be sent to the AI model (either ``text`` or ``file`` is required)
+* ``file`` (string): Path to a file containing the system prompt (either ``text`` or ``file`` is required)
 * ``include_tools`` (boolean, optional): When set to ``true``, tool definitions will be appended to the system prompt
 * ``enable_translation`` (boolean, optional): When set to ``true``, enables translation for the system prompt text (requires symfony/translation)
 * ``translation_domain`` (string, optional): The translation domain to use for the system prompt translation
 
+.. note::
+
+    You cannot use both ``text`` and ``file`` simultaneously. Choose one option based on your needs.
+
+**File-Based Prompts**
+
+For better organization and reusability, you can store system prompts in external files. This is particularly useful for:
+
+* Long, complex prompts with multiple sections
+* Prompts shared across multiple agents or projects
+* Version-controlled prompt templates
+* JSON-structured prompts with specific formatting
+
+Configure the prompt with a file path:
+
+.. code-block:: yaml
+
+    ai:
+        agent:
+            my_agent:
+                model: 'gpt-4o-mini'
+                prompt:
+                    file: '%kernel.project_dir%/prompts/assistant.txt'
+
+The file can be in any text format (.txt, .json, .md, etc.). The entire content of the file will be used as the system prompt text.
+
+**Example Text File** (``prompts/assistant.txt``):
+
+.. code-block:: text
+
+    You are a helpful and knowledgeable assistant.
+
+    Guidelines:
+    - Be clear and direct in your responses
+    - Provide examples when appropriate
+    - Be respectful and professional at all times
+
+**Example JSON File** (``prompts/code-reviewer.json``):
+
+.. code-block:: json
+
+    {
+      "role": "You are an expert code reviewer",
+      "responsibilities": [
+        "Review code for bugs and potential issues",
+        "Suggest improvements for code quality"
+      ],
+      "tone": "constructive and educational"
+    }
+
 **Translation Support**
 
 To use translated system prompts, you need to have the Symfony Translation component installed:

src/ai-bundle/src/AiBundle.php

@@ -50,6 +50,7 @@
 use Symfony\AI\Platform\Bridge\VertexAi\PlatformFactory as VertexAiPlatformFactory;
 use Symfony\AI\Platform\Bridge\Voyage\PlatformFactory as VoyagePlatformFactory;
 use Symfony\AI\Platform\Exception\RuntimeException;
+use Symfony\AI\Platform\Message\Content\File;
 use Symfony\AI\Platform\ModelClientInterface;
 use Symfony\AI\Platform\Platform;
 use Symfony\AI\Platform\PlatformInterface;
@@ -652,14 +653,28 @@ private function processAgentConfig(string $name, array $config, ContainerBuilde
         if (isset($config['prompt'])) {
             $includeTools = isset($config['prompt']['include_tools']) && $config['prompt']['include_tools'];
 
-            if ($config['prompt']['enable_translation']) {
-                if (!class_exists(TranslatableMessage::class)) {
-                    throw new RuntimeException('For using prompt translataion, symfony/translation package is required. Try running "composer require symfony/translation".');
-                }
+            // Create prompt from file if configured, otherwise use text
+            if (isset($config['prompt']['file'])) {
+                $filePath = $config['prompt']['file'];
+                // File::fromFile() handles validation, so no need to check here
+                // Use Definition with factory method because File objects cannot be serialized during container compilation
+                $prompt = (new Definition(File::class))
+                    ->setFactory([File::class, 'fromFile'])
+                    ->setArguments([$filePath]);
+            } elseif (isset($config['prompt']['text'])) {
+                $promptText = $config['prompt']['text'];
+
+                if ($config['prompt']['enable_translation']) {
+                    if (!class_exists(TranslatableMessage::class)) {
+                        throw new RuntimeException('For using prompt translataion, symfony/translation package is required. Try running "composer require symfony/translation".');
+                    }
 
-                $prompt = new TranslatableMessage($config['prompt']['text'], domain: $config['prompt']['translation_domain']);
+                    $prompt = new TranslatableMessage($promptText, domain: $config['prompt']['translation_domain']);
+                } else {
+                    $prompt = $promptText;
+                }
             } else {
-                $prompt = $config['prompt']['text'];
+                $prompt = '';
             }
 
             $systemPromptInputProcessorDefinition = (new Definition(SystemPromptInputProcessor::class))

src/ai-bundle/tests/DependencyInjection/AiBundleTest.php

@@ -835,11 +835,29 @@ public function testEmptyTextInArrayThrowsException()
         ]);
     }
 
-    #[TestDox('System prompt array without text key throws configuration exception')]
+    #[TestDox('System prompt array without text or file throws configuration exception')]
     public function testSystemPromptArrayWithoutTextKeyThrowsException()
     {
         $this->expectException(InvalidConfigurationException::class);
-        $this->expectExceptionMessage('The "text" cannot be empty.');
+        $this->expectExceptionMessage('Either "text" or "file" must be configured for prompt.');
+
+        $this->buildContainer([
+            'ai' => [
+                'agent' => [
+                    'test_agent' => [
+                        'model' => 'gpt-4',
+                        'prompt' => [],
+                    ],
+                ],
+            ],
+        ]);
+    }
+
+    #[TestDox('System prompt with only include_tools throws configuration exception')]
+    public function testSystemPromptWithOnlyIncludeToolsThrowsException()
+    {
+        $this->expectException(InvalidConfigurationException::class);
+        $this->expectExceptionMessage('Either "text" or "file" must be configured for prompt.');
 
         $this->buildContainer([
             'ai' => [