How to create a JSON API endpoint in Symfony

A small JSON endpoint gives a Symfony application a lightweight HTTP surface for health checks, frontend data, or simple integration callbacks without installing a full API framework. Returning JSON directly from a controller keeps the route, response status, and payload shape close to the application code that owns them.

Symfony routes incoming requests to controller actions. In a current Symfony Flex application, route attributes in controller classes are imported automatically, and AbstractController provides a json() helper that creates a JsonResponse with the JSON content type.

A GET /api/status route with an associative array root keeps the response as a JSON object for browser and API-client checks. Route inspection plus a local HTTP request confirm the URL, method, status, content type, and body before the endpoint is used by another service.

1. Create the controller file in the project.

   $ vi src/Controller/ApiStatusController.php

2. Add a GET route that returns a JSON response.

   ApiStatusController.php

   <?php
    
   namespace App\Controller;
    
   use Symfony\Bundle\FrameworkBundle\Controller\AbstractController;
   use Symfony\Component\HttpFoundation\JsonResponse;
   use Symfony\Component\HttpFoundation\Response;
   use Symfony\Component\Routing\Attribute\Route;
    
   final class ApiStatusController extends AbstractController
   {
       #[Route('/api/status', name: 'api_status', methods: ['GET'])]
       public function __invoke(): JsonResponse
       {
           return $this->json([
               'service' => 'catalog',
               'status' => 'ok',
           ], Response::HTTP_OK);
       }
   }

   The outer payload is an associative array, so the JSON root is an object rather than an indexed array.

3. Confirm that Symfony registered the route.

   $ php bin/console debug:router api_status
   +--------------+---------------------------------------------------------+
   | Property     | Value                                                   |
   +--------------+---------------------------------------------------------+
   | Route Name   | api_status                                              |
   | Path         | /api/status                                             |
   | Path Regex   | {^/api/status$}sDu                                      |
   | Host         | ANY                                                     |
   | Host Regex   |                                                         |
   | Scheme       | ANY                                                     |
   | Method       | GET                                                     |
   | Requirements | NO CUSTOM                                               |
   | Class        | Symfony\Component\Routing\Route                         |
   | Defaults     | _controller: App\Controller\ApiStatusController()       |
   | Options      | compiler_class: Symfony\Component\Routing\RouteCompiler |
   |              | utf8: true                                              |
   +--------------+---------------------------------------------------------+

   Symfony Flex imports route attributes from controller classes by default. If a prewarmed development cache does not show a newly added controller, clear the cache once with php bin/console cache:clear and rerun the route check.
   Related: How to create a Symfony route

4. Start the local Symfony web server.

   $ symfony server:start --no-tls --port=8000 -d
   [OK] Web server listening
        http://127.0.0.1:8000

   Use another free port when 8000 already belongs to another local project.
   Related: How to run a Symfony project locally

5. Request the endpoint and inspect the response.

   $ curl -i -sS http://127.0.0.1:8000/api/status
   HTTP/1.1 200 OK
   Content-Type: application/json
   ##### snipped #####
   
   {"service":"catalog","status":"ok"}

   The status line, Content-Type header, and response body confirm that Symfony returned the JSON endpoint. Copy only the response body into the validator when a browser-side JSON syntax check is useful.
   Tool: JSON Validator

6. Stop the local server after the smoke test.

   $ symfony server:stop
   [OK] Stopped the local web server