diff --git a/composer.json b/composer.json
index 5d1c5297..46ea2d77 100644
--- a/composer.json
+++ b/composer.json
@@ -32,9 +32,11 @@
     "psr/http-server-handler": "^1.0",
     "psr/http-server-middleware": "^1.0",
     "psr/log": "^1.0 || ^2.0 || ^3.0",
-    "symfony/finder": "^5.4 || ^6.4 || ^7.3 || ^8.0",
     "symfony/uid": "^5.4 || ^6.4 || ^7.3 || ^8.0"
   },
+  "suggest": {
+    "symfony/finder": "Required for file-based discovery."
+  },
   "require-dev": {
     "ext-openssl": "*",
     "composer/semver": "^3.0",
@@ -50,6 +52,7 @@
     "psr/simple-cache": "^2.0 || ^3.0",
     "symfony/cache": "^5.4 || ^6.4 || ^7.3 || ^8.0",
     "symfony/console": "^5.4 || ^6.4 || ^7.3 || ^8.0",
+    "symfony/finder": "^5.4 || ^6.4 || ^7.3 || ^8.0",
     "symfony/http-client": "^5.4 || ^6.4 || ^7.3 || ^8.0",
     "symfony/process": "^5.4 || ^6.4 || ^7.3 || ^8.0"
   },
diff --git a/src/Capability/Discovery/Discoverer.php b/src/Capability/Discovery/Discoverer.php
index 3b9ed3a9..b71d9c7c 100644
--- a/src/Capability/Discovery/Discoverer.php
+++ b/src/Capability/Discovery/Discoverer.php
@@ -66,6 +66,10 @@ public function __construct(
      */
     public function discover(string $basePath, array $directories, array $excludeDirs = []): DiscoveryState
     {
+        if (!class_exists(Finder::class)) {
+            throw new \RuntimeException('File-based discovery requires symfony/finder. Run: composer require symfony/finder');
+        }
+
         $startTime = microtime(true);
         $discoveredCount = [
             'tools' => 0,