Ensure the property field exists in tool input schemas

composer.json

@@ -80,7 +80,7 @@
             "pint --test",
             "rector --dry-run"
         ],
-        "test:unit": "pest --ci --coverage --min=91.2",
+        "test:unit": "pest --ci --coverage --min=91.4",
         "test:types": "phpstan",
         "test": [
             "@test:lint",

src/Server/Tool.php

@@ -57,14 +57,17 @@ public function toMethodCall(): array
     public function toArray(): array
     {
         $annotations = $this->annotations();
+        $schema = JsonSchema::object(
+            $this->schema(...),
+        )->toArray();
+
+        $schema['properties'] ??= (object) [];
 
         return [
             'name' => $this->name(),
             'title' => $this->title(),
             'description' => $this->description(),
-            'inputSchema' => JsonSchema::object(
-                $this->schema(...),
-            )->toArray(),
+            'inputSchema' => $schema,
             'annotations' => $annotations === [] ? (object) [] : $annotations,
         ];
     }

tests/Unit/Tools/ToolTest.php

@@ -72,6 +72,28 @@
     ]);
 });
 
+it('includes an empty properties object when the schema has no properties', function (): void {
+    $tool = new TestTool;
+    $array = $tool->toArray();
+
+    expect($array['inputSchema'])
+        ->toHaveKey('type', 'object')
+        ->toHaveKey('properties')
+        ->and($array['inputSchema']['properties'])->toEqual((object) []);
+});
+
+it('includes schema properties when defined', function (): void {
+    $tool = new ToolWithSchema;
+    $array = $tool->toArray();
+
+    expect($array['inputSchema']['properties'])
+        ->toHaveKey('message')
+        ->and($array['inputSchema']['properties']['message'])
+        ->toHaveKey('type', 'string')
+        ->toHaveKey('description', 'The message to echo')
+        ->and($array['inputSchema']['required'])->toEqual(['message']);
+});
+
 class TestTool extends Tool
 {
     public function description(): string
@@ -123,3 +145,13 @@ class CustomToolName extends TestTool
 {
     protected string $name = 'my_custom_tool_name';
 }
+
+class ToolWithSchema extends TestTool
+{
+    public function schema(\Illuminate\JsonSchema\JsonSchema $schema): array
+    {
+        return [
+            'message' => $schema->string()->description('The message to echo')->required(),
+        ];
+    }
+}