diff --git a/src/Middleware/ErrorFilter.php b/src/Middleware/ErrorFilter.php
index bf641d0b..dfcf2662 100644
--- a/src/Middleware/ErrorFilter.php
+++ b/src/Middleware/ErrorFilter.php
@@ -4,12 +4,16 @@
 
 namespace Horde\Core\Middleware;
 
+use Horde;
+use Horde\Http\ResponseFactory;
+use Horde\Http\StreamFactory;
+use Horde_ErrorHandler;
+use Horde_Registry;
 use Psr\Http\Message\ServerRequestInterface;
 use Psr\Http\Message\ResponseInterface;
 use Psr\Http\Server\MiddlewareInterface;
 use Psr\Http\Server\RequestHandlerInterface;
-use Horde_Registry;
-use Horde_Application;
+use Throwable;
 
 /**
  * ErrorFilter middleware
@@ -31,9 +35,58 @@
  */
 class ErrorFilter implements MiddlewareInterface
 {
+    protected Horde_Registry $registry;
+    protected ResponseFactory $responseFactory;
+    protected StreamFactory $streamFactory;
+
+    public function __construct(
+        Horde_Registry $registry,
+        ResponseFactory $responseFactory,
+        StreamFactory $streamFactory
+    ) {
+        $this->registry = $registry;
+        $this->responseFactory = $responseFactory;
+        $this->streamFactory = $streamFactory;
+    }
+
     public function process(ServerRequestInterface $request, RequestHandlerInterface $handler): ResponseInterface
     {
-        // TODO:
-        return $handler->handle($request);
+        try {
+            return $handler->handle($request);
+        } catch (Throwable $throwable) {
+            Horde::log($throwable, 'EMERG');
+            return $this->getErrorResponse($request, $throwable);
+        }
+    }
+
+    protected function getErrorResponse(ServerRequestInterface $request, Throwable $throwable): ResponseInterface
+    {
+        $isAdmin = $this->registry->isAdmin();
+        $acceptsJson = in_array('application/json', array_map(fn($val) => strtolower($val), $request->getHeader('Accept')));
+        if ($acceptsJson){
+            return $this->getJsonResponse($throwable, $isAdmin);
+        } else {
+            return $this->getHtmlResponse($throwable, $isAdmin);
+        }
+    }
+
+    protected function getJsonResponse(Throwable $throwable, bool $isAdmin = false): ResponseInterface
+    {
+        $json = json_encode([
+            'message' => $throwable->getMessage(),
+            'code' => $throwable->getCode(),
+            'trace' => $isAdmin ? $throwable->getTrace() : [],
+        ]);
+        $stream = $this->streamFactory->createStream($json);
+        return $this->responseFactory->createResponse(500, 'Internal Server Error')
+            ->withBody($stream)
+            ->withHeader('Content-Type', 'application/json');
+    }
+
+    protected function getHtmlResponse(Throwable $throwable, bool $isAdmin = false): ResponseInterface
+    {
+        $stream = $this->streamFactory->createStream(Horde_ErrorHandler::getHtmlForError($throwable, $isAdmin));
+        return $this->responseFactory->createResponse(500, 'Internal Server Error')
+            ->withBody($stream);
     }
 }
diff --git a/src/Middleware/HordeCore.php b/src/Middleware/HordeCore.php
index fc4ec53c..8ea22e6b 100644
--- a/src/Middleware/HordeCore.php
+++ b/src/Middleware/HordeCore.php
@@ -56,13 +56,15 @@ public function process(ServerRequestInterface $request, RequestHandlerInterface
             $injector->setInstance(ResponseFactoryInterface::class, new ResponseFactory());
         }
 
-
-        // Detect correct app
         $registry = $injector->getInstance('Horde_Registry');
-        $request = $request->withAttribute('registry', $registry);
+        // First middleware should be ErrorFilter to catch all errors
+        $handler->addMiddleware(new ErrorFilter($registry, new ResponseFactory(), new StreamFactory()));
+        // Detect correct app
         $handler->addMiddleware(new AppFinder($registry, new ResponseFactory(), new StreamFactory()));
         // Find route inside detected app
         $handler->addMiddleware(new AppRouter($registry, $injector->get('Horde_Routes_Mapper'), $injector));
+
+        $request = $request->withAttribute('registry', $registry);
         return $handler->handle($request);
     }
 }