diff --git a/pkgs/dart_mcp_server/README.md b/pkgs/dart_mcp_server/README.md
index 8431c3e0..48223891 100644
--- a/pkgs/dart_mcp_server/README.md
+++ b/pkgs/dart_mcp_server/README.md
@@ -160,6 +160,6 @@ For more information, see the official VS Code documentation for
 | `run_tests` | Run tests | Run Dart or Flutter tests with an agent centric UX. ALWAYS use instead of `dart test` or `flutter test` shell commands. |
 | `set_widget_selection_mode` | Set Widget Selection Mode | Enables or disables widget selection mode in the active Flutter application. Requires "connect_dart_tooling_daemon" to be successfully called first. This is not necessary when using flutter driver, only use it when you want the user to select a widget. |
 | `signature_help` | Signature help | Get signature help for an API being used at a given cursor position in a file. |
-| `stop_app` |  | Kills a running Flutter process started by the launch_app tool. |
+| `stop_app` |  | Stops a running Flutter process started by the launch_app tool. |
 
 <!-- generated -->
diff --git a/pkgs/dart_mcp_server/lib/src/mixins/flutter_launcher.dart b/pkgs/dart_mcp_server/lib/src/mixins/flutter_launcher.dart
index 00cf5e2e..9def4d8f 100644
--- a/pkgs/dart_mcp_server/lib/src/mixins/flutter_launcher.dart
+++ b/pkgs/dart_mcp_server/lib/src/mixins/flutter_launcher.dart
@@ -243,11 +243,11 @@ base mixin FlutterLauncherSupport
   final stopAppTool = Tool(
     name: 'stop_app',
     description:
-        'Kills a running Flutter process started by the launch_app tool.',
+        'Stops a running Flutter process started by the launch_app tool.',
     inputSchema: Schema.object(
       properties: {
         'pid': Schema.int(
-          description: 'The process ID of the process to kill.',
+          description: 'The process ID of the process to stop.',
         ),
       },
       required: ['pid'],
@@ -255,7 +255,7 @@ base mixin FlutterLauncherSupport
     outputSchema: Schema.object(
       properties: {
         'success': Schema.bool(
-          description: 'Whether the process was killed successfully.',
+          description: 'Whether the process was stopped successfully.',
         ),
       },
       required: ['success'],
@@ -274,8 +274,33 @@ base mixin FlutterLauncherSupport
         content: [TextContent(text: 'Application with PID $pid not found.')],
       );
     }
-
-    final success = processManager.killPid(pid);
+    // On Unix, killing the flutter process doesn't kill the entire process
+    // group, so we have to look for the child processes.
+    if (Platform.isLinux) {
+      final ps = processManager.runSync([
+        'ps',
+        '--no-headers',
+        '--format',
+        '%p',
+        '--ppid',
+        '$pid',
+      ]);
+      if (ps.exitCode == 0) {
+        final children = (ps.stdout as String).trim().split('\n');
+        if (children.isNotEmpty) {
+          for (final child in children) {
+            int childPid;
+            try {
+              childPid = int.parse(child);
+            } on FormatException {
+              continue;
+            }
+            processManager.killPid(childPid, ProcessSignal.sigterm);
+          }
+        }
+      }
+    }
+    final success = processManager.killPid(app.process.pid);
     if (success) {
       log(
         LoggingLevel.info,
diff --git a/pkgs/dart_mcp_server/test/tools/flutter_launcher_test.dart b/pkgs/dart_mcp_server/test/tools/flutter_launcher_test.dart
index 09ae3656..7c25f0a5 100644
--- a/pkgs/dart_mcp_server/test/tools/flutter_launcher_test.dart
+++ b/pkgs/dart_mcp_server/test/tools/flutter_launcher_test.dart
@@ -318,7 +318,7 @@ void main() {
             'test-device',
           ],
           stderr: 'Something went wrong',
-          exitCode: Future.value(1),
+          exitCode: 1,
         ),
       );
       final serverAndClient = await createServerAndClient(
@@ -505,6 +505,15 @@ void main() {
           pid: processPid,
         ),
       );
+      if (Platform.isLinux) {
+        mockProcessManager.addCommand(
+          Command(
+            ['ps', '--no-headers', '--format', '%p', '--ppid', '$processPid'],
+            stdout: '11111\n22222\n',
+            pid: processPid,
+          ),
+        );
+      }
       final serverAndClient = await createServerAndClient(
         processManager: mockProcessManager,
         fileSystem: fileSystem,
@@ -533,9 +542,12 @@ void main() {
         CallToolRequest(name: 'stop_app', arguments: {'pid': processPid}),
       );
 
-      test.expect(result.isError, test.isNot(true));
       test.expect(result.structuredContent, {'success': true});
-      test.expect(mockProcessManager.killedPids, [processPid]);
+      test.expect(mockProcessManager.killedPids, [
+        if (Platform.isLinux) ...[11111, 22222],
+        processPid,
+      ]);
+      test.expect(result.isError, test.isNot(true));
       await server.shutdown();
       await client.shutdown();
     });
@@ -688,7 +700,7 @@ class Command {
   final List<String> command;
   final String? stdout;
   final String? stderr;
-  final Future<int>? exitCode;
+  final int? exitCode;
   final int pid;
 
   Command(
@@ -720,7 +732,9 @@ class MockProcessManager implements ProcessManager {
       }
     }
     throw Exception(
-      'Command not mocked: $command. Mocked commands:\n${_commands.join('\n')}',
+      'Command not mocked: "${command.join(' ')}".\n'
+      'Mocked commands:\n'
+      '${_commands.map<String>((e) => e.command.join(' ')).join('\n')}',
     );
   }
 
@@ -743,7 +757,9 @@ class MockProcessManager implements ProcessManager {
       stdout: Stream.value(utf8.encode(mockCommand.stdout ?? '')),
       stderr: Stream.value(utf8.encode(mockCommand.stderr ?? '')),
       pid: pid,
-      exitCodeFuture: mockCommand.exitCode,
+      exitCodeFuture: mockCommand.exitCode != null
+          ? Future(() => mockCommand.exitCode!)
+          : null,
     );
     runningProcesses[pid] = process;
     return process;
@@ -770,7 +786,7 @@ class MockProcessManager implements ProcessManager {
     final mockCommand = _findCommand(command);
     return ProcessResult(
       mockCommand.pid,
-      await (mockCommand.exitCode ?? Future.value(0)),
+      mockCommand.exitCode ?? 0,
       mockCommand.stdout ?? '',
       mockCommand.stderr ?? '',
     );
@@ -789,7 +805,14 @@ class MockProcessManager implements ProcessManager {
     Encoding? stdoutEncoding = systemEncoding,
     Encoding? stderrEncoding = systemEncoding,
   }) {
-    throw UnimplementedError();
+    commands.add(command);
+    final mockCommand = _findCommand(command);
+    return ProcessResult(
+      mockCommand.pid,
+      mockCommand.exitCode ?? 0,
+      mockCommand.stdout ?? '',
+      mockCommand.stderr ?? '',
+    );
   }
 }