[Server] Use compact JSON in result formatters

CHANGELOG.md

@@ -16,6 +16,7 @@ All notable changes to `mcp/sdk` will be documented in this file.
 * Fix `Session::save()` wiping the other keys of a session that the store failed to read, e.g. when `Psr16SessionStore` hits a cache error: it now returns `false` instead of writing the changed keys alone.
 * Fix `EnumCompletionProvider` and `ListCompletionProvider` offering all values for the prefix `"0"` instead of only the values that start with it.
 * Fix tools, prompts and resources sending `content`, `messages` and `contents` as a JSON object instead of an array when the handler returned a non-list array, e.g. the result of `array_filter()`. Named keys in nested results of mixed arrays no longer overwrite each other.
+* Tool, prompt and resource results and `TextContent` encode arrays and objects as compact JSON instead of pretty-printed JSON.
 * Add `Psr6SessionStore` and `Psr6NotificationBus`, which work like `Psr16SessionStore` and `Psr16NotificationBus` over a PSR-6 cache pool. `Builder::setDiscovery()` also accepts a PSR-6 pool as `$cache`.
 
 ### Client

src/Capability/Formatter/PromptResultFormatter.php

@@ -173,7 +173,7 @@ private function formatContent(mixed $content, ?int $index = null): TextContent|
             return new TextContent($stringContent);
         }
 
-        $jsonContent = json_encode($content, \JSON_PRETTY_PRINT | \JSON_UNESCAPED_SLASHES | \JSON_UNESCAPED_UNICODE | \JSON_THROW_ON_ERROR);
+        $jsonContent = json_encode($content, \JSON_UNESCAPED_SLASHES | \JSON_UNESCAPED_UNICODE | \JSON_THROW_ON_ERROR);
 
         return new TextContent($jsonContent);
     }

src/Capability/Formatter/ResourceResultFormatter.php

@@ -155,7 +155,7 @@ public function format(mixed $readResult, string $uri, ?string $mimeType = null,
             if ($mimeType && (str_contains(strtolower($mimeType), 'json')
                 || 'application/json' === $mimeType)) {
                 try {
-                    $jsonString = json_encode($readResult, \JSON_THROW_ON_ERROR | \JSON_PRETTY_PRINT);
+                    $jsonString = json_encode($readResult, \JSON_THROW_ON_ERROR);
 
                     return [new TextResourceContents($uri, $mimeType, $jsonString, $meta)];
                 } catch (\JsonException $e) {
@@ -164,7 +164,7 @@ public function format(mixed $readResult, string $uri, ?string $mimeType = null,
             }
 
             try {
-                $jsonString = json_encode($readResult, \JSON_THROW_ON_ERROR | \JSON_PRETTY_PRINT);
+                $jsonString = json_encode($readResult, \JSON_THROW_ON_ERROR);
                 $mimeType = $mimeType ?? 'application/json';
 
                 return [new TextResourceContents($uri, $mimeType, $jsonString, $meta)];

src/Capability/Formatter/ToolResultFormatter.php

@@ -97,7 +97,7 @@ public function format(mixed $toolExecutionResult): array
 
         $jsonResult = json_encode(
             $toolExecutionResult,
-            \JSON_PRETTY_PRINT | \JSON_UNESCAPED_SLASHES | \JSON_UNESCAPED_UNICODE | \JSON_THROW_ON_ERROR | \JSON_INVALID_UTF8_SUBSTITUTE
+            \JSON_UNESCAPED_SLASHES | \JSON_UNESCAPED_UNICODE | \JSON_THROW_ON_ERROR | \JSON_INVALID_UTF8_SUBSTITUTE
         );
 
         return [new TextContent($jsonResult)];

src/Schema/Content/TextContent.php

@@ -40,7 +40,7 @@ public function __construct(
         public readonly ?Annotations $annotations = null,
     ) {
         $this->text = (\is_array($text) || \is_object($text))
-            ? json_encode($text, \JSON_PRETTY_PRINT) : (string) $text;
+            ? json_encode($text) : (string) $text;
 
         parent::__construct('text');
     }

tests/Integration/ClientExamples/ClientExampleTestCase.php

@@ -11,6 +11,7 @@
 
 namespace Mcp\Tests\Integration\ClientExamples;
 
+use Mcp\Tests\Support\PrettyJson;
 use PHPUnit\Framework\Attributes\DataProvider;
 use PHPUnit\Framework\TestCase;
 use Symfony\Component\Process\Process;
@@ -66,7 +67,7 @@ public function testOutputMatchesSnapshot(string $input): void
             $process->getErrorOutput(),
         ));
 
-        $this->assertMatchesSnapshot($this->normalizeOutput($process->getOutput()));
+        $this->assertMatchesSnapshot($this->normalizeOutput($this->prettyPrintJson($process->getOutput())));
     }
 
     /**
@@ -82,6 +83,15 @@ protected function normalizeOutput(string $output): string
         return $output;
     }
 
+    private function prettyPrintJson(string $output): string
+    {
+        return preg_replace_callback(
+            '/^(\s*(?:Content: )?)(\{.*\})$/m',
+            static fn (array $match): string => $match[1].PrettyJson::format($match[2]),
+            $output,
+        ) ?? $output;
+    }
+
     private function assertMatchesSnapshot(string $output): void
     {
         $className = substr(static::class, strrpos(static::class, '\\') + 1);

tests/Interop/Server/InspectorSnapshotTestCase.php

@@ -13,6 +13,7 @@
 
 use Mcp\Schema\Enum\LoggingLevel;
 use Mcp\Tests\Interop\NodeTool;
+use Mcp\Tests\Support\PrettyJson;
 use PHPUnit\Framework\Attributes\DataProvider;
 use PHPUnit\Framework\TestCase;
 use Symfony\Component\Process\Process;
@@ -97,7 +98,7 @@ public function testOutputMatchesSnapshot(
 
         $snapshotFile = $this->getSnapshotFilePath($method, $testName);
 
-        $normalizedOutput = $this->normalizeTestOutput($output, $testName);
+        $normalizedOutput = $this->normalizeTestOutput($this->prettyPrintTextFields($output), $testName);
 
         if (!file_exists($snapshotFile)) {
             file_put_contents($snapshotFile, $normalizedOutput.\PHP_EOL);
@@ -116,6 +117,19 @@ protected function normalizeTestOutput(string $output, ?string $testName = null)
         return $output;
     }
 
+    private function prettyPrintTextFields(string $output): string
+    {
+        $result = json_decode($output);
+
+        foreach ([...$result->content ?? [], ...$result->contents ?? []] as $item) {
+            if (isset($item->text)) {
+                $item->text = PrettyJson::format($item->text);
+            }
+        }
+
+        return json_encode($result, \JSON_THROW_ON_ERROR);
+    }
+
     public static function provideMethods(): array
     {
         return [

tests/Support/PrettyJson.php

@@ -0,0 +1,27 @@
+<?php
+
+/*
+ * This file is part of the official PHP MCP SDK.
+ *
+ * A collaboration between Symfony and the PHP Foundation.
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Mcp\Tests\Support;
+
+/**
+ * Keeps JSON readable in snapshots; formatter tests pin the compact wire format.
+ */
+final class PrettyJson
+{
+    public static function format(string $text): string
+    {
+        $decoded = json_decode($text);
+
+        return \is_array($decoded) || \is_object($decoded)
+            ? json_encode($decoded, \JSON_PRETTY_PRINT | \JSON_UNESCAPED_SLASHES | \JSON_UNESCAPED_UNICODE | \JSON_THROW_ON_ERROR)
+            : $text;
+    }
+}

tests/Unit/Capability/Formatter/PromptResultFormatterTest.php

@@ -123,6 +123,13 @@ public function testFormatRoleContentArray(): void
         $this->assertSame(Role::User, $result[0]->role);
     }
 
+    public function testFormatArrayContentAsCompactJson(): void
+    {
+        $result = (new PromptResultFormatter())->format(['role' => 'user', 'content' => ['key' => ['nested' => 1]]]);
+        $this->assertInstanceOf(TextContent::class, $result[0]->content);
+        $this->assertSame('{"key":{"nested":1}}', $result[0]->content->text);
+    }
+
     public function testFormatTypedTextContentPreservesAnnotations(): void
     {
         $result = (new PromptResultFormatter())->format([

tests/Unit/Capability/Formatter/ResourceResultFormatterTest.php

@@ -46,6 +46,17 @@ public function testFormatResourceContents(): void
         $this->assertSame([$contents], $result);
     }
 
+    public function testFormatArrayResultAsCompactJson(): void
+    {
+        $result = (new ResourceResultFormatter())->format(['key' => ['nested' => 1]], 'test://uri', 'application/json');
+        $this->assertInstanceOf(TextResourceContents::class, $result[0]);
+        $this->assertSame('{"key":{"nested":1}}', $result[0]->text);
+
+        $result = (new ResourceResultFormatter())->format(['key' => ['nested' => 1]], 'test://uri');
+        $this->assertInstanceOf(TextResourceContents::class, $result[0]);
+        $this->assertSame('{"key":{"nested":1}}', $result[0]->text);
+    }
+
     public function testFormatWithMimeType(): void
     {
         $result = (new ResourceResultFormatter())->format('content', 'file://test', 'text/html');

tests/Unit/Capability/Formatter/ToolResultFormatterTest.php

@@ -52,7 +52,7 @@ public function testFormatArrayResult(): void
         $result = (new ToolResultFormatter())->format(['key' => 'value']);
         $this->assertCount(1, $result);
         $this->assertInstanceOf(TextContent::class, $result[0]);
-        $this->assertStringContainsString('value', $result[0]->text);
+        $this->assertSame('{"key":"value"}', $result[0]->text);
     }
 
     public function testFormatNullResult(): void

tests/Unit/Schema/Content/TextContentTest.php

@@ -0,0 +1,28 @@
+<?php
+
+/*
+ * This file is part of the official PHP MCP SDK.
+ *
+ * A collaboration between Symfony and the PHP Foundation.
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Mcp\Tests\Unit\Schema\Content;
+
+use Mcp\Schema\Content\TextContent;
+use PHPUnit\Framework\TestCase;
+
+final class TextContentTest extends TestCase
+{
+    public function testArrayIsEncodedAsCompactJson(): void
+    {
+        $this->assertSame('{"key":{"nested":1}}', (new TextContent(['key' => ['nested' => 1]]))->text);
+    }
+
+    public function testObjectIsEncodedAsCompactJson(): void
+    {
+        $this->assertSame('{"key":"value"}', (new TextContent((object) ['key' => 'value']))->text);
+    }
+}