-

src/Chain/ToolBox/ToolBox.php

@@ -56,7 +56,7 @@ public function execute(ToolCall $toolCall): string
                         return json_encode($result, flags: JSON_THROW_ON_ERROR);
                     }
 
-                    if (is_integer($result) || is_float($result)) {
+                    if (is_integer($result) || is_float($result) || $result instanceof \Stringable) {
                         return (string) $result;
                     }
 

tests/Chain/ToolBox/ToolBoxTest.php

@@ -18,6 +18,7 @@
 use PhpLlm\LlmChain\Tests\Fixture\Tool\ToolReturningFloat;
 use PhpLlm\LlmChain\Tests\Fixture\Tool\ToolReturningInteger;
 use PhpLlm\LlmChain\Tests\Fixture\Tool\ToolReturningJsonSerializable;
+use PhpLlm\LlmChain\Tests\Fixture\Tool\ToolReturningStringable;
 use PHPUnit\Framework\Attributes\CoversClass;
 use PHPUnit\Framework\Attributes\Test;
 use PHPUnit\Framework\Attributes\UsesClass;
@@ -43,6 +44,7 @@ protected function setUp(): void
             new ToolReturningJsonSerializable(),
             new ToolReturningInteger(),
             new ToolReturningFloat(),
+            new ToolReturningStringable(),
         ]);
     }
 
@@ -133,6 +135,13 @@ public function toolsMap(): void
                     'description' => 'A tool returning a float',
                 ],
             ],
+            [
+                'type' => 'function',
+                'function' => [
+                    'name' => 'tool_returning_stringable',
+                    'description' => 'A tool returning an object which implements \Stringable',
+                ],
+            ],
         ];
 
         self::assertSame(json_encode($expected), json_encode($actual));
@@ -193,4 +202,13 @@ public function executeWithToolReturningFloat(): void
             $this->toolBox->execute(new ToolCall('call_1234', 'tool_returning_float'))
         );
     }
+
+    #[Test]
+    public function executeWithToolReturningStringable(): void
+    {
+        self::assertSame(
+            'Hi!',
+            $this->toolBox->execute(new ToolCall('call_1234', 'tool_returning_stringable'))
+        );
+    }
 }

tests/Fixture/Tool/ToolReturningStringable.php

@@ -0,0 +1,21 @@
+<?php
+
+declare(strict_types=1);
+
+namespace PhpLlm\LlmChain\Tests\Fixture\Tool;
+
+use PhpLlm\LlmChain\Chain\ToolBox\Attribute\AsTool;
+
+#[AsTool('tool_returning_stringable', 'A tool returning an object which implements \Stringable')]
+final class ToolReturningStringable
+{
+    public function __invoke(): \Stringable
+    {
+        return new class implements \Stringable {
+            public function __toString(): string
+            {
+                return 'Hi!';
+            }
+        };
+    }
+}